RAD Expansion Unit for Commodore 64/128

I have wanted a REU for my Commodore 64 and 128, but they haven’t been reasonable to get an original. I also has not seen a reproduction option. Yes there are a few options, but nothing I was going to get into. I recently came across Frntc’s RAD Expansion Unit Project. I recently saw the Sidekick64 and had been wondering what it was, what advantage does it have to other similar products. It turns out in the US you can’t buy built versions of his projects (short of shipping and fees from Europe). If you are in Europe there are authorized resellers of the RAD Expansion Unit.

The RAD EU uses a Raspberry pi, either a Pi3 or Pi Zero2 to emulate a REU / Ram Expansion Unit. It can work at various sizes up to 16Mb, it can also work as Georam. It can do REU Images, which I am not familiar with, and NUVIEs and says it can run PRG. I take it the PRG is normal PRG files. NUVIEs are 16mb movie files which I have not tried. My intention for this device is to use it as a REU to run some programs I couldn’t otherwise run on my Commodore 64 / 128. I am thinking of trying out Geos as well with it.

Frntc has released the Gerber files for getting PCBs produced. It is highly recommended to get the Gold Plated ENIG boards. While the HASL Solder coated fingers are very common, they are common because they are cheap, not because they are recommended. Most or even all of the aftermarket Cartridges I have are HASL, they generally work, but use of them makes the solder rub off into your cartridge slot and will cause problems over time. The boards I had produced awhile ago were also HASL. I hadn’t been having issues with them on my C64, but I don’t swap cartridges often. I did find my C128 was very unreliable using the cartridges, which may be due to another reason.

I had a spare Pi3 A+, I do also have a single Pi Zero2, but I felt it is more useful for some other projects. I ordered up Frntc’s board design for the pi3 model with the Gold Plate ENIG board finish.

The gold looks very nice. It is a much more constant finish on the edge connecter. I can see how these boards are certainly an upgrade for edge connector boards. For boards without the edge connector I will keep using the HASL finish. It is generally a difference for example from $2 to $19 for a small batch of boards.

Frntc provides a file call ibom.html in the Gerber folder that is an interactive Bill of Materials. It lists the basic part and footprint data for it. I wish he had used more universal footprints, some of these surface mount footprints can be setup to accept either the wider ics or the narrower ICs giving more valid part options. It took me awhile looking at the parts on Digikey and Mouser to find the ICs with the proper footprint for the boards.

I found all the right parts eventually. I was going to order from Digikey, but they didn’t have one of the ICs in stock. I went with Mouser as they had everything in stock. The pricing was generally close between the two suppliers. I did mess up and miss ordering some of things I had sitting in a cart at Digikey that I wanted to put on my next order though.. The parts all came in and it turns out everything was correct. I will list the specific Parts I ordered here.

Notes: The 10k Ohm resistors are 0805 parts not 603 an oddity in the part number I guess.. The Capacitors are all 0805 as well. One of the HTC30 ICs and it’s capacitor are not listed as required on the ibom. I found a picture of the board where that IC is outlined in the silkscreen as “optional”. I put them on, I wonder if it is for debugging or development? It was $0.45 in parts basically, so I didn’t see a major reason to not install them.

I had an issue with the firmware. I figured it would be in the repository where it would download with it repository. That is how it has been for the few other projects that I have used. The code is in the repository if you download it, but not the compiled release. I am not very familiar with Github, maybe no one else will have an issue finding it without this little note. It turns out Releases are along the right hand side bar on Github. Since I had the issue finding it, I asked 8-bit Resurgence where the files were. So to get the compiled files, Click on “Releases” at the Github project page on the right hand bar, assuming they don’t change the location.

The soldering wasn’t too bad. I did try a new solder tip with the solder cavity in it for drag soldering. I found it was putting down two much solder and was difficult to remove a bridge with. I went back to my normal tip without that hollow in the bottom of it. I did use a paste flux, which I am do often use a bit less flux. I did find cleaning up the flux with 91% ipa wasn’t the easiest. It just didn’t do a great job and took a few passes. There was flux stuck inside the pi Header, you may be able to see it on the picture above still in the header. The next day I used contact cleaner on the header and ics. It flushed a lot of the flux out of the header, it also flushed a lot of flux out from under the ics that I didn’t know as still under there.

It works.

Now it needs a case. There is a case design linked with the project. I started printing it in a slightly translucent blue PLA. The label on it was printed on plain paper as a test with double sided tape on the back. Overall the case looked pretty good, it also fit well. I decided I wanted something that blended more with the Commodore 64.

I ordered in Polymaker Matte PLA Filament 1.75mm Muted White Filament to see how that looked. It was recommended by Macintosh Librarian as a good matching color for the early Macintosh. I figured it will not be a color match, but it should be in a good color range to “fit in” better than the blue case.

I also had a small piece of Inkjet Vinyl. My old HP Inkjet printer is out of black ink, and the new color cartridge isn’t working well, probably due to how old it is even though I just installed it. It is also quite an old printer that Windows 10 doesn’t care to print to it properly. I had to tape the small piece to a piece of paper to put it through the printer. Which it did well with that. I’m debating buying fresh cartridges for it.

I like the new case a lot better. The label is much nicer too. I like the color, it is a light beige. It is not a “match” to the Commodore 64 Breadbin color, it is probably fairly close to the Commodore 128 or Commodore 64C. I can’t tell though, as my Commodore 128 is Yellow.. The Commodore 64 Breadbin I am using it in is lighter than the typical Breadbin because it has been Painted. The RAD EU is a bit lighter than the paint, but looks very nice with it. I did print the case at .28mm layer height, so printing at lower layer heights may make a little nicer looking case.

Flat Commodore 128 From 16k to 32k ROMs and Switchless JiffyDOS Kernal

I have been wanting to put JiffyDOS on my Commodore 128. My 1541ii came with JiffyDOS, but none of my Commodore Computers did. I recently purchased JiffyDOS from RETRO Innovations, I am also doing a 4 way Switchless JiffyDOS setup on my Commodore 64.

The Commodore 128 Flat model shipped setup with 16k ROMs, it can be switched over to using 32k ROMs by setting some jumpers. If you switch it to 32k ROMs then there are only 2 ROMs required instead of 4. The ROMs that shipped in the Commodore 128 Flat model area also older than what is available. I wanted to update the Basic ROM, and the Kernal as well, so it is nice to only need two eproms instead of four.

In this case I am going to switch to the 32k ROMs, and also install a Switchless JiffyDOS ROM.

To change the Commodore 128 Flat from 16kB ROMs to 32kB ROMs we just have to install jumpers or bridge J3, J4, and J6. I am going to put in Jumpers to make it easy to switch back if needed. You will find instructions at various sources that tell you to do a mod that will connect the one jumper differently (J4) so that you can use the Commodore 128DCR ROM. I found that they did apparently make a Commodore 128 “Flat/D” 32k ROM, well I can’t tell where it came from, but it is listed like it has a Commodore Part Number. I decided to go with just putting in the jumpers for J3, J4 and J6 using the C128 “Flat/D” specific ROM. You can alternately make this slightly different ROM, it is about the order of the data on it.

To setup the JiffyDOS 32K ROM Set. We pull U33 (16k) and U34 (16k) and install the 32k U34 to replace them. That new ROM is the basic.390393-01.bin (32kB).

The second ROM we pull the 16K U32 and U35. Since I am doing the JiffyDOS Switchable ROM, I am making a 64K ROM to replace the original U32.

Switched C128/C128DCR KERNAL ROM (64kB):
basic.901226-01.bin (C64 Basic)
kernal.901227-03.bin (C64 Kernal)
kernal.318020-05.bin (C128 Kernal)
basic.901226-01.bin (C64 Basic)
JiffyDOS_C64_6.01.bin (C64 JiffyDOS Kernal)
JiffyDOS_C128DCR_6.01.bin (C128 JiffyDOS Kernal)

To do the Switched ROM we keep Pin1 (A15) bent out, and not inserted in the Socket. If I was going to do a Kernal “Switch”, then I would wire a 4.7k (recommended value I found) Resistor from Pin1 (A15) to Pin28 (VCC). Then put a switch between Pin1 and Ground. I am going to use an Arduino Pro Mini, it will not need the Pullup Resistor. I expect you could do Kernal Switcher that does more than two modes by making a 128K ROM, but for the Commodore 128 I don’t know of other Kernals that I care to use. That would also be a 32PIN Eprom so an adapter would also be required. If you did stick with the 16k ROMs, you could then alternately use 64k Eproms to setup a 4 way ROM Switcher.

I am basing the Arduino Pro Mini code on a modified version of Adrian Black’s C64 Kernal Switcher. It will be modified to only switch between two modes instead of four. I am starting with Mark Ormond’s modified version of the code as the basis. I only need to trigger switching A15 on one Eprom. It was setup to control 2 Eproms and rotate through more ROMs triggering several Address lines. With 16k ROMs on the Commodore 128 you do need to control 2 different ROMs. The board will be wired with a Current Limiting Resistor to the PowerLED to show the status changes. It will be triggering A15 on the 64k ROM triggering it to use either the upper or lower 32k portion. It will also be wired to the ResetLine, EXROMLine and RestoreKey, as well as Ground and 5V.

Above is the starting point. We have the four 16k ROMs installed. The first part of this modification is to remove them and install the jumpers to switch the system over to 32k ROM mode. That is just adding the 3 jumpers to the board.

There was a bit of an issue with that, the pins are not standard jumper pin spacing, I slightly bent the bottom part of the jumper to get it inserted. I do know there is a smaller size jumper I have seen on other equipment, but I don’t have the pins or jumpers to put on them. After bending the pins a bit they did fit well. I then got out some spare jumpers and installed them. By using the jumpers I can easily switch to 16k ROMs again if I want.

The next thing I had to do was put in the connections for the Switchless Kernal Switcher. It also handles doing a Hard Reset, well it is supposed to. I don’t know how it works with the Commodore 128 as I have only seen such mods on Commodore 64s. I wanted to make it removable, so I put in pins where I could, even to the point of putting pins on the side of two of the 74 logic ICs. That made it so I can detach the Pro Mini board and go back to normal ROMs, be it 32k or 16k ROMs. Also if the Pro Mini fails I can more easily switch it out. Be sure to get a 5V Pro Mini, not a 3.3V model.. The only wire directly soldered to the Pro Mini without a connector on the other end is for the Eprom, but it is socketed itself, so not a huge deal.

The last pin is Pin 1 of the new U32. It needs to kept out of the socket and wired to the Pro Mini pin5.

U32 Pin 1 is Not in the Socket, is it connected just to the white wire.

Above you can see the new 64k Switched U32, and the 32k U34 in place. It may not be visible but Pin 1 on U32 is Not in the Socket, it is sticking out on the side and not making contact to the socket. The wire there goes over to Pin5 on the Pro Mini. Since I am using the Pro Mini, as I mentioned there is no Pullup Resistor from Pin 1 to Pin 28 on U32 like would be done with a “switch” based JiffyDOS setup.

I have modified Adrian/Mark’s code so that by default it will do a 4 way Kernal Switch for the Commodore 128. That can only be done with 16k ROMs though. Mark had it setup for 16k ROMs with a 4 way switch for only 1 of the ROMs and only doing 2 way for the second. That has a use, being you can use a smaller Eprom for the 2 way mode, but my version would have to be modified to do that. It now does a 4 way switch for both Commodore 128 16k ROMs by default. I added a “Max ROMs” entry that is set to 4 by default, but for my use I set that to 2 as I am using 32k ROMs and only have 2 sets of ROMs. Well I set it for 2 the second time around, I thought I messed up the code when it was trying to do a 4 way switch initially. I miswired the U32 Pin 1 to the wrong output of the Pro Micro, so I had to fix that too. Other than those two little issues it worked.

There is also the oddity that when it resets, the Commodore 128 goes into 64 Mode. Maybe it doesn’t like the Exrom Reset? It does properly remember the selected Kernal, and it does go into 128 mode when powered on based on the saved Kernal setting, the factory Reset button on the 128 also takes you to 128 Mode. You may catch that the RF Modulator was changed out on the pictures, you can also find the post other recent post about the RF Mod. The RF Modulator change was certainty worth it for the video quality improvement for 40 Column output. I did all of the changes at the same time.

I’m going to work on getting the code uploaded to Github as a branch to Mark’s release. I plan to add some instructions and pictures. Mark does have his pictures and a guide posted at another site, but he has the code at Github.

I am not certain the code below is correct for 16k 4 way switching for the C128 or not. I was getting U35 and U32 etc all mixed up when working on it. It is the code I compiled and used on my 2 way, except below it is set for 4 way switching with that one variable “NumROMs”.

#include <EEPROM.h>

// C64/C128 Kernel Switcher and Restore Key Reset/Selector
// Version 1.3 - 03-26-2023 Updates - By Travis Durf

// Based on C64 Kernel Switcher - 26-March-2019 - By Adrian Black
// Restore Key Mod: https://www.breadbox64.com/blog/c64-restore-mod/
// Initial C128 Changes - 06-22-2020 - By Mark Ormond aka dabone

             "The Simple" Pro-Mini

           DTR  TX   RX   VCC  GND  GND
        |  [ ]  [ ]  [ ]  [ ]  [ ]  [ ]  |
        |              FTDI              |
    D1  | [ ]1/TX                 RAW[ ] |    
    D0  | [ ]0/RX                 GND[ ] |    
        | [ ]RST        SCL/A5[ ] RST[ ] |   C6
        | [ ]GND        SDA/A4[ ] VCC[ ] |    
    D2  | [ ]2/INT0    ___         A3[ ] |   C3
    D3  |~[X]3/INT1   /   \        A2[ ] |   C2
    D4  | [X]4       /PRO  \       A1[ ] |   C1
    D5  |~[X]5       \ MINI/       A0[ ] |   C0
    D6  |~[X]6        \___/    SCK/13[ ] |   B5
    D7  | [X]7                MISO/12[ ] |   B4
    B0  | [X]8      [RST-BTN] MOSI/11[ ]~|   B3
    B1  |~[X]9  GND[ ]A6[ ]A7[ ]SS/10[X]~|   B2
Based on: http://busyducks.com/ascii-art-arduinos

D3 to EXROMLine (C128 U11 (PLA) Pin12)
D4 to PowerLED to 220 Ohm resistor to Power LED
D5 to C64 A13, C128 U32 (A14) Pin27 
D6 to C64 A14 27256(32kB), C128 U32 (A15) Pin1 With 27512(64kB) EEPROM 32kB ROMs
D7 to ResetLine (C128 U63 Pin2)
D8 to RestoreKey (C128 U16 Pin9)
D9 to C128 U35 (A14) Pin27
D10 to C128 U35 (A15) Pin1 With 27512(64kB) EEPROM 16kB ROMs

Set "NumROMs" to be the Maximum Number of ROMs.  2-4 Default is "4"

For Commodore 64:
To do 4 ROM Sets you can use a 27256(32kB) EEPROM with A13 and A14
You can use a 27128(16kB) EEPROM and do 2 ROM Sets with A13.

For Commodore 128:
To do 4 ROM Sets on a stock C128 Flat that uses 16k ROMs you can use 27512(64kB) EEPROMs with A14 and A15
You can use 27256(32kB) EEPROMs and do 2 ROM Sets with A14.

For C128 Flat/D set to 32kB ROMs, or DCR (Both use 32kB ROMs), you can use 27512(64kB) EEPROMs to do 2 ROM sets with A15. 
When doing 32kB C128 ROMs you only use U32 and only use A15 as A14 is kept in the Socket and controlled by the C128.
U35 is removed in the 32kB ROM configuration and is now included in the 32kB based U32 now.  The drawback here is you can only
do two ROM Sets with the 27512 EEPROMs.
The C128 Basic ROMs must be replaced with a new 32kB Basic ROM (basic.390393-01.bin) in U34, also removing U33.


const int EXROMLine = 3;    // Output the /EXROM line
const int PowerLED = 4;     // Output Power LED
const int PowerLEDAlt = 13; // Output Power LED (onboard LED)
const int RomAOne = 5;      // Output EPROM C64 A13 (C128 16kB Mode U32 Pin27 A14, 32kB Mode U32 Pin1 A15)
const int RomATwo = 6;      // Output EPROM C64 A14 (C128 16kB Mode U32 Pin1 A15 27512 EEPROM)
const int ResetLine = 7;    // Output to /RESET line
const int RestoreKey = 8;   // Input Restore key
const int RomBOne = 9;      // Output EEPROM C128 16kB U35 Pin27 A14
const int RomBTwo = 10;     // Output EEPROM C128 16kB U35 Pin1 A15 27512 EEPROM

int RestoreDelay = 2000;    // 2000ms delay for restore key
const int FlashSpeed = 75;  // LED Flash delay

const unsigned long repeatdelay = 500; // used for debouncing
const int NumROMs = 4;		// Maximum Number of ROMs
int CurrentROM;				// which rom is select (0-3)
int debouncecounter = 0;	// how many times we have seen new value (for debounce)
int debouncereading;
int debounce_count;
int RestoreHeld;
unsigned long TimeHeld;     // amount of time Restore is held down

int buttonDuration = 0;     // for keeping track of how long restore is held down
boolean buttonHeld = 0;     // for keeping track when you are holding down 
boolean Released = 0;       // Keeping track when the restore key is released
boolean holdingRestore = 0; // Keeping track if you are holding restore
boolean resetSystem = 0;    // keep track whether to reset

int buttonInput;            // used to return if restore is held
unsigned long time;         //used to keep track of millis output
unsigned long htime;        //used to keep track of millis output
unsigned long btime;        //used to keep track of bounce millis output

void setup() {
  pinMode(PowerLED, OUTPUT);
  pinMode(PowerLEDAlt, OUTPUT);
  pinMode(RomAOne, OUTPUT);
  pinMode(RomATwo, OUTPUT);
  pinMode(RomBOne, OUTPUT);
  pinMode(RomBTwo, OUTPUT);
  pinMode(ResetLine, INPUT);
  pinMode(EXROMLine, INPUT);
  pinMode(RestoreKey, INPUT);

  digitalWrite(PowerLED, HIGH); // turn on the power LED

  digitalWrite(ResetLine, LOW); // keep the system reset
  pinMode(ResetLine, OUTPUT);   // switch reset line to OUTPUT so it can hold it low
  digitalWrite(ResetLine, LOW); // keep the system reset

  CurrentROM = EEPROM.read(1);
  pinMode(ResetLine, INPUT);    // set the reset pin back to high impedance which releases the INPUT line
  delay(1000);                  // wait 1000ms 
  FlashLED(CurrentROM);         // flash the power LED to show the current state
  // all set!

void loop() {
  buttonInput = readButton(); delay(500);
  time = millis(); // load the number of milliseconds the arduino has been running into variable time
  if (buttonInput == 1) {
    if (!buttonHeld) {
      htime = time; TimeHeld = 0; buttonHeld = 1; } //restore button is pushed
    else { 
      TimeHeld = time - htime; } // button is being held down, keep track of total time held.
  if (buttonInput == 0) {
    if (buttonHeld) {
      Released = 1; buttonHeld = 0; htime = millis(); TimeHeld = 0; //restore button not being held anymore
  if (TimeHeld > RestoreDelay && !Released) { // do this when the time the button is held is longer than the delay and the button is released
    htime = millis();
    if (holdingRestore == 0) { FlashLED(CurrentROM); holdingRestore = 1; resetSystem = 1; } // first time this is run, so flash the LED with current slot and reset time held. Set the holding restore variable.
    else {
      if (CurrentROM < NumROMs - 1) { CurrentROM++; SaveSlot(CurrentROM); } // or you've already been holding restore, so increment the current ROM slot otherwise reset it to 0
      else { CurrentROM = 0; SaveSlot(CurrentROM); }
      if (TimeHeld > RestoreDelay) { TimeHeld = 0;}  // reset the time held
      FlashLED(CurrentROM); //flash the LED
  if (Released) {
    //if time held greater than restore delay, reset the system, set the current rom slot, reselt the time held and holding restore
    if (resetSystem) { // on do this if the reset system has been set above
      htime = millis();
      resetSystem = 0;
      holdingRestore = 0;
      Released = 0;
      digitalWrite(ResetLine, LOW); // keep the system reset
      digitalWrite(EXROMLine, LOW); // keep the EXROM line low
      pinMode(ResetLine, OUTPUT);
      pinMode(EXROMLine, OUTPUT);
      digitalWrite(ResetLine, LOW); // keep the system reset
      digitalWrite(EXROMLine, LOW); // keep the EXROM line low
      delay(50); // wait 50ms
      SetSlot(CurrentROM); // select the appropriate kernal ROM
      delay(200); // wait 200ms before releasing RESET line
      pinMode(ResetLine, INPUT); // set the reset pin back to high impedance so computer boots
      delay(300); // wait 300ms before releasing EXROM line
      pinMode(EXROMLine, INPUT); // set the reset pin back to high impedance so computer boots
    } else { //otherwise do nothing
      htime = millis(); Released = 0; resetSystem = 0; holdingRestore = 0;
// finished with loop  

int readButton() {
 if (!digitalRead(RestoreKey) && (millis() - btime >= repeatdelay)) {
  for(int i = 0; i < 10; i++)
      debouncereading = !digitalRead(RestoreKey);

      if(!debouncereading && debouncecounter > 0)
      // If the Input has shown the same value for long enough let's switch it
      if(debouncecounter >= debounce_count)
        btime = millis();
        debouncecounter = 0;
        RestoreHeld = 1;
    delay (10); // wait 10ms
   } else {
    RestoreHeld = 0;
return RestoreHeld;

void SaveSlot(int CurrentRomSlot) {
  // Save Current ROM selection (0-3) into EPROM

void FlashLED(int flashcount) {
    // Flash the LED to represent which ROM slot is selected
    switch (flashcount) {
    case 0:
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
    case 1:
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
    case 2:
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
    case 3:
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);
      digitalWrite(PowerLED, LOW);
      digitalWrite(PowerLEDAlt, LOW);
      digitalWrite(PowerLED, HIGH);
      digitalWrite(PowerLEDAlt, HIGH);

void SetSlot(int DesiredRomSlot) {
    // Select the actual ROM slot being used
    switch (DesiredRomSlot) {
    case 0:
      digitalWrite(RomAOne, LOW);
      digitalWrite(RomATwo, LOW);
      digitalWrite(RomBOne, LOW);
      digitalWrite(RomBTwo, LOW);
    case 1:
      digitalWrite(RomAOne, HIGH);
      digitalWrite(RomATwo, LOW);
      digitalWrite(RomBOne, HIGH);
      digitalWrite(RomBTwo, LOW);
    case 2:
      digitalWrite(RomAOne, LOW);
      digitalWrite(RomATwo, HIGH);
      digitalWrite(RomBOne, LOW);	  
      digitalWrite(RomBTwo, HIGH);
    case 3:
      digitalWrite(RomAOne, HIGH);
      digitalWrite(RomATwo, HIGH);
      digitalWrite(RomBOne, HIGH);
      digitalWrite(RomBTwo, HIGH);
      digitalWrite(RomAOne, LOW);
      digitalWrite(RomATwo, LOW);
      digitalWrite(RomBOne, LOW);
      digitalWrite(RomBTwo, LOW);

While I was working on the Commodore 128, I had been having issues with the Cartridge Port reading correctly. So while I had the board out I reflowed all the pins on the cartridge port. Upon getting the Kernal Switcher (and RF Modulator change) done I put in two different cartridges and both worked properly the first time. I’m hoping this means my Commodore 128 is in good working order now. It is annoying not being able to use cartridges reliably. I do have JiffyDOS now. I need to try it out with my 1541ii that has a Vintage JiffyDOS rom in it. I also purchased JiffyDOS for the 1541, and will be putting it on my pi1541 and trying that out. But not tonight, it is way to early in the morning to start that, I am going to go get some sleep. I was nice getting a number of these projects wrapped up today/ in the last 24hours.

I realized I forgot to show a JiffyDOS 128 80 Column RGB Video screen shot. You see it adds the JiffyDOS line to the startup screen there.

Commodore 64 326298 Rev A 1982(FAB 326295 Rev D) Reset Mod and Switchless Kernal Mod

The Commodore 64 326298 Rev A has a different reset circuit. The 556 is wired in with a way that it keeps the reset line pulled to 5V and will supply as much current to that as it can. There are various ways to rework the circuit from over the years. I was looking at the least invasive way to accomplish this. I ran across a post on the Backbit Forum, as this reset being the way it is prevents the Backbit cartridge from working properly. It also affects other cartridges that use the Reset or have Reset buttons integrated into them. When they try to pull Reset to Ground the 556 works hard to keep it from resetting. It may crash the computer or cause glitches, probably as much as anything because it pulls the 5V line down starving the computer for power.

The process posted on the forum was to install a 1k Resistor in R36. This is a pull up resistor that keeps the Reset line pulled to 5V but “gently”. If it is missing the system could randomly reset, or be stuck in reset. The second part is to disconnect Pin9 on the 556 IC. We only want to disconnect the pin, the “wire” that is in the board there needs to remain connected. The simplest and easiest way to accomplish this would be to cut the leg off the 556. I didn’t want to do that.

What I ended up doing was desoldering the 556 from the board. I then took a 14pin machine pin IC Socket and clipped the bottom of Pin9 from it. I then paced he modified socket into the board so that Pin9 on the 556 is not going to the board. The Wire though is still going from the Pin9 Pad to Pin13 but that wire is no longer making contact with Pin9 of the 556. I then installed the 556 into the socket. On power on the system didn’t work. I checked the work, and then also tested the 556. The 556 had failed, it may have been during desoldering it, but it also may be that a portion of the 556 had been damaged by trying to use the Reset button on my cartridge. It may still have worked with Pin9 connected. I did have a spare so I tested the replacement and installed it. On powering it up the system worked normally again. I also tested using the reset button on the cartridge and that worked properly now. R36 is installed, it is a 1.5k resistor, a special precision one I have a small stock of, as I was short on 1k resistors at the time.

I believe if I had not done the Reset Modification that my next Modification, the Switchless Kernel ROM probably wouldn’t have worked normally. It also pulls Reset low, which it couldn’t sink all the current required to overcome the 556 previously.

C38 was previously replaced with a 4.7nF capacitor when I replaced the Electrolytic Capacitors to make the Restore key responsive. With the factory 51pF capacitor you have the hit the Restore key quite hard to get it to register usually, I don’t know if that would in any way affect the Kernal Switcher, as I haven’t seen it said that mod needs to be done. I did it as part of the recaping process based on it being recommended by Console5 where I purchased the kit. It did work as described, I tested both before and after switching that capacitor out.

Kernel Switcher:

The I am using bwak’s SKS64 “C64-Switchless-Multi-Kernal-27C256-adapter” project. This is a custom PCB that works as an adapter to install a 27256 as a 4 way Kernal ROM replacement. It is controlled with an ATTiny85, an early version used a PIC instead. I happened to have some ATTiny85s and liked the idea of using one for this. There are also ATMega based Arduino type board options out there. I am using a Pro Mini Arduino board for my Commodore 128 Switchless Kernal. This ATTiny was a neater solution for this, it is a all-in-one optkoon as we already need an adapter board to convert the 27256 to work with the Commodore 64.

It has very good documentation at his Github page. There are considerations on what order your solder the parts together. He does cover that in his documentation.

The documentation shows where you can tap into the required signals on the C64 mainboard. The Reset, Restore and EXRom lines. Keep in mind the images below are for the 326298 Rev A, the guide from bwak shows similar images of all the various board types for reference.

I preped the board putting in single angled pin headers for the three signals and replaced the old single wipe socket for the Kernal ic. Of course I messed up and used the only socket I had, which you can see in the picture is solid in the center so the ATTiny85 on the bottom of the adapter can’t go in place.. So I have to replace it again, this time with machine pin header strips, as I don’t have an appropriate machine pin or other hollowed out socket to put on the board.

Opps wrong socket..

Since I had the wrong socket, I had to use the Turn Pin socket strips.

Now that the socket problem is sorted, I can get the adapter installed.

Switcher with the required header wires.

I was glad I was able to use some premade dupont cables I had. They are actually all premade cables from my breadboard cables I have. For the LED cable I just swapped the single dupont plastic holder for a tripple holder. There is an issue with just using the stock Red LED, but for now it works.

Note: I quickly replaced the Stock Red LED with a RGB LED, while it worked and the pictures in this section are showing the wiring for that, you only had the LED on if it was in Kernal 1, so the computer didn’t give an indication on the case that the power was on. The code could be change to always keep the RED LED on and just blink, but I didn’t want to look into what that involved. I just went with swapping to the RGB LED as I had them anyways.

The documentation is a lacking information on making the file to program the Eprom. You can get information from bwak on doing similar things by looking at the documentation on his VersaCart project. I’ll cover some basics blow.

The 27c256 is a 32k Eprom that can hold four 8k Kernal ROMs. I program the Eprom with my TL866ii plus.

To prepare the bin file for the Eprom. I collected them all in the same folder. I am using the Stock Kernal for the first one, then JiffyDos from RetroInovations, MasterRom 64, and JaffyDos (customized JiffyDos). Taking those 4 files in a folder, then open a Command Prompt window and while in the folder with the files use the command below. This is for the exact filenames I had, so your do need to be sure to enter the filenames you have instead. The U4_32KuB.bin is the 32k bin file I will use with my TL866ii to program the 27c256 Eprom. The code below it all in 1 line, if it is wrapped to two or more lines when viewing this page keep that in mind.

copy /b kernal.901227-03.bin+JiffyDOS_C64_6.01.bin+MASTEROM64_V3.0.BIN+jaffydos.bin U4_32KuB.bin

I will say JaffyDOS was a bit annoying to create. I couldn’t find proper instructions on how to accomplish it. JaffyDOS is created with a Commodore 64 .prg. You need to run it from the Commodore 64 Vice Emulator. You answer some customization settings once you manage to get it mounted properly and get it to where it can find your “JiffyDOS_C64_6.01.bin” which it has to be able to access. Running it properly will then create the jaffydos.bin file in the same folder as “JiffyDOS_C64_6.01.bin” had been located in. I did find some apparently outdated and possibly incomplete instructions and fumbled through getting the prg in Vice and the folder where the JiffyDOS bin was.

Once you have the 32k bin it is a simple task to use the TL866ii to burn the data to the Eprom. I will not go into detail on that, it is easy to find instructions on using at TL866 to program an Eprom or EEprom etc.

So the next bit that was a bit lacking in the documentation is programming the ATTiny85. You need to setup the Arduino IDE to be able to use the ATTiny85, and use bwak’s files to compile the program file. bwak does cover that you need to disable the Reset pin on the ATTiny if you want to use the EXRom function which enables doing a Hard Reset rather than the standard “Soft” Reset, if you are just using the Arduino IDE to program the ATTiny, then I don’t know how you disable the Reset pin, I think one or more of the ATTiny board types can do that. The ATTiny core I use for Arduino apparently doesn’t, or doesn’t make it obvious how to to it. The main reason I expect is they don’t want it to be easy for you to accidentally doing it without knowing that you will no longer be able to program the ATTiny with the Arduino IDE you will then have to use a HV(High Voltage) Programmer. If you have a TL866ii, it is a HV Programmer, it can set the Reset disable fuse, and also enable reset again if needed as well. He does cover that in his document. I actually used the Arduino IDE to program the ATTiny85, then used the TL866ii Plus to disable the ATTiny’s Reset pin fuse. You can also use the TL866ii to upload the Hex file created by the Arduino IDE though, which is in bwak’s document.

For now I just have the Stock LED in place. I will have to finish wiring up a RGB LED so I can then see which ROM is enabled by looking at it. I was hoping it would just keep the standard LED enabled, maybe somewhere in the code there is an option to tell it to just use the RED LED, I didn’t notice it though. The board looks like it is intended to be alternately used with the Stock LED though.

Beyond the LED being off for all but the First ROM (the Stock ROM in my case) it is working great. I’ll get that LED wired up and installed shortly. I have the right RGB LED, I just didn’t get around to making it up initially, I really didn’t want to make it up. I may look at the Code and see if there is an option to change the LED output behavior it is about as easy to make up the RGB LED as it is to pull the chip and recompile the code.

Commodore 128 / Commodore 64 Shortboard RF Module Replacement

I have been unhappy with the regular 40 Column video output on my Commodore 128. Watching a video by TheRetroChannel on Youtube, I saw his RF Module replacement. I feel technically that is not the right thing to call these types of boards, they “replace” the RF Module, but they are not “Replacement RF Modules”. You loose the “RF” Output, this really isn’t an issue as not many people would likely want to ever connect up the Commodore 128/64 by RF to an old TV tuned to Channel 3/4.

He released the board designs on Github as open source projects. There are two versions the C64 Longboard and the C64 Shortboard/C128 versions. For the Commodore 128 I needed the short board version, so I ordered them from JLCPCB. This is specifically the board that fits the Commodore 64 Short Board and Commodore 128 as they share the same type of Modulator. He also made a Commodore 64 Long Board version, they are basically the same but the Long Board version is a bit larger pcb to fit the Long Board properly.


The boards have various options on them. I have populated everything except the C64 Hard Reset section. This is for a Commodore 128 after all, and it already has a reset button. That isn’t a Hard Reset though, but by the time I install this that also won’t be an option. It is indicated it may not work on the C128 though I don’t know if that is the case or not.

I put on the 500 Ohm Trimmer Pots rather than the default resistors. I had the exact parts in stock, and I have a fair quantity of them, I purchased them for some project, maybe even when I was working on the earlier RGBI Adapter builds years ago. I did set them to match the set resistors as a starting point. The center and “right” pin have to be set to the baseline value, 75 Ohm and 180 Ohm I believe. I don’t know if I will have to do any adjustments on them or not, but I had them and it made sense to me to use them. I probably have more of those Trimmers than resistors of the correct values anyways. This whole board was populated with parts I had in stock, the Audio jack was salvaged, but everything else is new. It was neat having a project I had everything for.

It was a strait forward build, everything is labeled. The two capacitors are labeled on the bottom of the board instead of the top, that did have me almost putting them in the wrong locations. It is easy to transpose the positions when flipping something over. I know he mentioned he made is so that the parts would cover up most of the silk screen markings. When assembled it does look pretty nice too. The only other thing I did check which pins on the Trimmers needed the proper baseline resistance set on them, but that was easy. I picked the White boards as I thought it would look nice when installed as well. It won’t clash with the color of the C128 board, or look like some poor attempt to color match it.

I am going to start with the normal Chroma/Luma paths. I will test that everything is working properly there, then I plan to switch to the External Chroma/Luma lines. The whole reason I am doing this modification is to try to improve the poor video quality I get from the VIC 40 Column video output. My Commodore 64s have far superior Video Output to the C128.

I really don’t need the SVideo and 3.5mm Audio Jack output. I have my RGBI Video Adapter which already has level adjusted SVideo and the SVideo jack (which is why I had a spare SVideo jack in my stash of parts), plus the Audio Jack on it. It won’t hurt to have them. It was unclear as to if the Chroma/Luma output on the Commodore AV Port was still active, but looking at the Schematics and board itself it is still connected.

Again, it was an easy build. TheRetroChannel does say the hard part of this mod is removing the RF Modulator module from the C128/64 board. He is correct, I have removed three of them, and well it is not something I look forward to.

I desoldered the factory RF Modulator, and stuck in the new unit. I fit it without soldering. The pins helped hold it reasonably secure so it wasn’t sliding around. So I did a test fit, and put the board in the case to get it lined up to the openings properly.

You can see that it is crooked in relation to the board. This is due to the alignment of the holes in the case having the opening for the “switch” lower than the “RF” port opening. Once I had it set where I wanted it, I carefully removed the boards from the case. I then tacked some of the pins with a bit of solder. I fitted it back inside the case again to make sure it didn’t move. Then I removed it from the case again and finished soldering it in. It was not difficult to align the board, as the pins held it fairly firmly in place as there are 12 pins they gave enough friction to not have it flop around while I was lifting it out of the case or flipping it over to solder.

It is in and the pins are all cut down properly. It was time to test it. I wanted to get some pictures of the output before switching out the modulator, but I forgot.. I fully remember it was awful in comparison to both of my Commodore 64s even in SVideo output. I was hoping I had some pictures of testing the SVideo output when I built the new RGBI adapter. I didn’t take pictures of the SVideo output. It was still awful at the time..

There is a jumper on the board to enable the Composite video, I believe the Chroma line to it. If you are just going to use SVideo, having it disabled is to slightly improve the output. I forgot to install it and ended up with the first screen above, basically no color except the “noise” around the text. The second shot is the Composite after putting the Jumper on. The last being SVideo output. The SVideo is much cleaner with no noise around the text. Even the Composite is a huge improvement over having the RF Modulator installed.

I wish I had some pictures of the Before. It is dramatic in this case. I was going to do the Chroma / Luma Bypass, those two pins on the lower right of the board. Without doing that, the video is comparable to my Commodore 64s. I feel it isn’t worth it at this point. I don’t want to bend out the VIC’s Chroma and Luma pins from the socket and solder wires to them. The improvement as it is was totally worth it. The two trimmer potentiometers are left set on the 180 and 75 ohm settings, I didn’t see a reason to adjust either at this point. I figure your probably safe to put in the standard resistors for those unless you want to go all out and tweak it to perfection. The same wit the Chroma / Luma bypass. You can still see Jailbars on the display, they are far better and overall the image is much sharper and cleaner.

Flat Commodore 128 Maintenance and 64k VDC Ram Upgrade

When I purchased my first Commodore 64 I also purchased a Commodore 128 Flat type model. The Commodore 128 worked when it arrived. It was complete and in the original box. It is quite yellowed, after cleaning it looks a little better, but is still very yellow. I did the kind of Maintenance I had done with the Commodore 64s.

Pulling the board, cleaning the case with soap and water. I pulled all of the keys from the keyboard and cleaned them and the keyboard frame. The capacitors were all replaced with a kit from Console 5. Two capacitors had residue under them. I also pulled the cover and frame from around the VIC/VDC area. I did not reinstall the RF Shields, I did install heatsinks on various of the ICs that tend to get warm. For the heatsinks I filed an angle on the Pin 1 corner. I also painted that angled area to make it stand out and painted the IC Part on the side of the heatsink to know what ICs they are if they are removed.

The heatsinks came from Console5 as well. They are attached with “THERMALLY CONDUCTIVE HEAT SINK ADHESIVE GLUE“. To identify Pin1 when they are installed, I have Filed the corner of the heatsink a bit where Pin1 is and they painted the filed edge with a Sharpie Paint Marker (Not a Permanent Marker as they “fade” with time). I also paint the IP Part on the side of the heatsink to identify them.

When I installed the Heatsinks on my first Commodore 64 I had not filed the corner or labeled the ICs. I just went by they were in the right place already and that I wasn’t planning to remove them. I believe they can be separated, but it would be risking damage to the chips, and I don’t know how well the glue can be removed once fully cured. I went with the Glue on type of heatsink, in a small part is I could get them. The main reason I liked the Glue on type is I feel more confident in the “thermal glue” being “Thermally Conductive” as intended than the double sided tape used on other heatsinks. I am not real good with the paint marker, and it is a rather blunt marker. The paint seems to work well and last better than a Permanent Marker. With the Thermal Glue, you don’t want it any thicker than it has to be for the best thermal transfer. With about any thermal transfer material it is best to keep it as thin as possible. Before installing the heatsinks I do like to make sure I have good pictures of all the chips, that way I can look up date codes and revisions etc if I want to in the future.

For bolt on heatsinks such as the regulators, I do use modern thermal paste to replace the old white paste. Not the Liquid Metal stuff that eats the metal surfaces though.

The 64k Ram upgrade for the 80Column mode is quite easy. There are two ram chips that need to be desoldered from the board. Then I soldered in IC Sockets and put in the new Ram Chips. The Ram can be checked with a basic program to ensure it is active. Yes there is a “no soldering required” 64k Ram upgrade, this is a carrier board that you pull the VDC from the socket and install it where the VDC is then reinstall on the board.

From Ray Carlsen’s site:

One way to tell if you have the upgraded VRAM is with a little BASIC
program typed in 80 column mode:
If the screen says: READY and looks normal, you have 64K of VRAM. If you
have only 16K, the screen will fill up with zeros.

Ray Carlsen CET Carlsen Electronics

To test the Commodore 128 I made up one of the modified VersaCart boards with some Commodore 128 Diagnostic ROMs. It is one of the spare boards I had left over, setup with two different versions of the diagnostics. For the Versa Cart as I set it up, I closed JP8 A15, JP10 A14, ROML, J5 set to Switch. Resistor installed for A13, and the last switch installed to toggle between the two ROMs.

I did have issues with the cartridge making good contact. You may see in the first picture there is another cartridge sitting under it, slightly wedging it upward. I looked at the cartridge port, it looks fine, I cleaned it with contact cleaner, I checked all around and can not find why it is being problematic. I’ll be looking at the port more. I had the same problems with other cartridges. With being careful to get good contact, and the C64 harness connected everything passed though. I later found out you shouldn’t get the solder coated PCBs, you need to order them with Gold Plated contacts to get good contact. Without looking, I am not sure any of my modern cartridges have Gold Plated contacts. I don’t use them often, but they have worked what little bit I use them fine in my 64s. Many though aren’t wanting to work properly in this C128. I do have some old cartridges, and the original PCB that my one Commodore cartridge does have Gold Contacts. I have had issue with the Atari 2600 with certain original solder plated cartridges being far far more problematic, and need serious cleaning to get working well.

When doing my next project on this C128, I resoldered all the points on the cartridge connector. I can’t see anything wrong with it, it looks to be clean, doesn’t look like any of the pins/contacts are bent or pushed out to far etc. It has been cleaned with contact cleaner several times. I did then test one of my original cartridge games and it worked properly, I don’t remember if I used that specific one previously, and I haven’t tried the C128 Diag Cart again at this point.

Commodore 128 RGBI/CGA to Analog RGB Part 4: A New Case

Part 1: Prototype Post

Part 2: PCB Design, Schematics and BOM

Part 3: Boards Assembly and Testing

The KiCad files, Gerbers, Schematics, Bill of Materials and 3d Models are all released at Github:

I worked up some 3D Printable Cases for the C128 RBGI/CGA to Analog RGB Adapter boards.

I am trying to get away from TinkerCAD, the AMpI4 case (See the post on that here) that I made in TinkerCAD turned out for me. It was a lot of work and it is complex to make modifications to that model when I need/want to.

This time I went back to DesignSpark Mechanical, which is what I started with for the AMpI4 case. I wasn’t ready for a project like that as my first real attempt to make anything in it. This time it was painful as well, but it is a much easier project. I learned a fair bit, but have a long way to go. The case hasn’t turned out perfect, but I’m quite happy with it overall. I make make a couple adjustments to it yet. To start with a made up a mockup of the physical board. That took awhile, then I realized I could export a 3d model of the board from KiCad. When I found that option, I went back and partially started over. I then just had to model the various ports. I did not size them to real world size, I upsized them to be used as the penetrations in the case exterior.

I ended up with making two prototype case prints. The first one showed me the primary mistakes. The SVideo Mini DIN Port opening was too small. The port was accessible with it being properly uncovered, but the outer plastic of the SVideo cable couldn’t get into the opening as it has to go down flush to the port. The RCA ports were correct, they don’t go the whole way down around the outside. The 5V Barrel jack was properly sized for 3 different power cables I tested with it. The DE9 was right. The screw holes placement for the HD15 port were 1mm to high, the whole port was 1mm to high, the cutout and all. This may be due to me using the DE9 measurements as the basis for both openings. I resized the Mini DIN opening, dropped the screw holes for the HD15 port and made the case thicker overall. The first case closed properly, all port alignments were right (short of the HD15 height), the mounting holes for the board and the posts were all correct. I made those adjustments and printed another test of what is now the “all” version of the case. The revised case printed out well, the Mini DIN Port cable now fit properly, the screws for the HD15 were aligned properly and the case was not as flimsy feeling. Once that all checked out, I went back into DesignSpark Mechanical and made up my variant cases from the initial “all” openings case. It was easy to make those variants as it only took a couple minutes. If I was familiar with it I bet it would be more like 2 minutes to do the modifications. I am still very unfamiliar with it, but I like the greater control with the model compared to TinkerCAD.

There are 3 versions of the case, the “all”, the “CGA” and the “C128” variants.

The “all” case has openings for all of the ports.

As you can see the case design is a split top case. There are no overhangs (except the DB/DE screw holes and the underside holes) that require support when printing. There is a slight rounding on the corners. With the settings I am using on my printer it takes about around 1.5hours per half of the case. I normally print faster on my Ender 3 Pro, but the filament I am using didn’t like that. It is some old PLA+ and that particular filament always gets moisture in it. To speed up the process I ended up printing each half on one of my two printers. That is why the filament is different for each, as I didn’t have two spools of the same color. I printing in PLA/PLA+ incase I wanted to paint the case. The color is an acceptable color for the use though. I plan on making up a version of the labels I put on my prototype to put on the tops of the cases. I’ll have to get ink cartridges in the printer before I an make the labels up though. The DE9/HD15 ports have the holes for the standoffs in the lower case shell. The bottom of the case has 4 holes in it for screws to go up through into the standoffs on the top half of the case to keep it shut. I don’t put the Standoffs in tight until I have the bottom screws in to prevent cracking something. With the case design, it does take opening the case to move the jumpers of course. I’d rather not have holes in the top for stuff to fall in, it is also hard swap jumpers in openings like that. It may be possible to rework the PCB to have some sort of DIP Switch. That makes another part to have to source, but it is possible to use that footprint for Jumpers too. DIP Swithes though are generally SPST, not SPDT which is what three of those jumpers need. I do have “mini” SPDT Switches, which I actually intended to install into the C128 type board, but I forgot to. They fit the 3pin Pin Header footprint, and have a narrow somewhat tall slide. These are used on some Commodore 64 (and I am sure other) New and Reproduction cartridges such as my C64 Diag/DeadTest Cartridge. I have also used them on some cartridges, like the C128 Multi Diag Cartridge I made awhile ago. For those mini switches it could be possible to design a case top that let you change them either with small openings, or even make extension caps that let you toggle the switches with the case closed. I don’t expect to be switching the configuration of the adapters often. The SCART to HDMI adapter was unstable in testing the games and was said to introduce lag, I’ll likely just use these with my GBS Control adapter instead. I’d love to be able to use them with my Sony PVM, but it takes a 4V Sync signal, I haven’t even looking at what may be done to adapt that from the ~1V Sync that normally is put out with RGBI/CGA.

The “C128” case is modified to accept my slightly custom RGBI board and has openings for the four Commodore 128 specific ports along the left side. It doesn’t have an opening for the DE9 Male port, as I am using a short “dongle” type cable out the side. It has a smaller opening where the 5V DC barrel jack would be and a second matched opening beside that for my two “dongle” cables grommets to rest in.

I use the short “dongle” cables there for the C128 version as I don’t want to have to make up short stubby cables to plug into ports. I also don’t want to make a custom Commodore AV Cable of some type. It gets more complex trying to find a port and jack for the Commodore AV Cable, then everyone who wants to make one needs to source the same “odd” port and jack. It is bad enough getting the Commodore AV Port “U” DIN connector. Since I am using that short AV dongle there is no good reason to make up a shot stubby DE9 Male to Female cable either. In my case that is part of an old DE9 Serial Modem cable. The grommets fit the cables snuggly and are from a case of grommets I picked up at Harbor Freight. I sized the holes to accept those grommets.

The third type of case is the “CGA” Case. It doesn’t have any of the Commodore 128 ports on the side, but has all the other normal openings in it. The case should be easy to modify with various 3d modeling packages, even with Tinkercad or such if you want different openings.

The case isn’t perfect but I’m happy with it. The holes in the bottom were meant to take recessed M3 screws. The recesses aren’t deep, or wide enough. I have already printed 4 cases today for just 2 adapters, so I don’t plan to rework the recesses. I also don’t have any tapered M3 screws of an appropriate length. It seems to close well with M3 screws, I made the holes in the top standoffs to be hollowed out quite deeply, but something like a 10mm or probably 8mm screw is sufficient. My cases are printed out of PLA on two different printers and the holes worked well on both, the holes are a good fit for the M3 screws on both, but each printer is a bit different. I thought of putting Brass Standoffs in, which takes a larger hole, but there is alot of variation on what size and depth they need to be. It is hard to make a “universal” case when using brass standoffs. I have some super cheap thin ones, them my good ones are massive.. When sitting the case together there is a slight pulling at the corners, but on putting the screws in the minor gaps close up tightly. With my cases the fact it is made of two different materials does make it stand out a bit, but I kind of like the look. It should print fine in PETG. I used PLA as I have more color options, and if I decide I want to color match it with paint, PLA is the better option. I like doing prints in Transparent PETG, but this is for use with an 80s Era Computer not an iMac. I have a couple opaque PETG filaments, but not one in a color that I felt was appropriate.

Above are pictures of the closed up cases from various angles. I also showed some bottom views where the screws are present. It is quite bland looking and you can’t tell what it is for by just looking at it. I want to make labels similar to the prototype, but I’ll need ink for the printer before making them.

After assembly I did some testing with the Commodore 128 with my GBS Control (see post on that for details) taking the 80 Column output the rest of the way to standard VGA.

I did test the Monochrome Composite 80 Column Output after doing my bodge on the V1.2 board the Monochrome Composite 80 Column worked properly after. The Monochrome 80 Column is fixed on the released V1.3 Board design. I really don’t know why anyone would use it, it can very easily be used just connecting directly to the pin on the RGBi Video Port. I only added it because I could.

The KiCad files, Gerbers, Schematics, Bill of Materials and 3d Models are all released at Github:

I went back and finally looked at H2Obsession’s “Ultimate” adapter project. He included a “Dark Gray” fix as well. I wasn’t aware there was an issue with Dark Gray. I’ll have to look at it and see why that was done. It should be simple enough to add. I’m also thinking about the PVM taking 5V CSync for RGB. I’m wondering if I could come up with an option for that.

Here are a few pictures of the Commodore 128 setup. It is a bit crowded with projects, most of them have posts here on the blog. The Commodore 64 replacement Power Supply, a Commodore 64 to Commodore 128 Power Supply Adapter cable (I don’t have post about it, It takes the C64 power jack on once side and the Commodore 128 plug is from “Hey Birt!“. My C64 power supplies were built for higher current than the factory model making them able to handle the C128’s requirement fine. I used Drunk “n” Retro’s Diagram, which you can find many examples of diagrams to do so ). I do have the serviced Commodore 128 Power Supply, but it is easier to just swap in the adapter cable, than having both out on the desk. The Commodore 128 is connected to the Samsung 940MW TV I repaired. I of course have the RGBI Adapter tucked in under the monitor. I do have the Monochrome Composite 80 column connected up to the TV, as I was testing it. I also have the 40 Column SVideo connected to the TV. The RGBI Adapter is connected across to the GBS Control (silver box on the right under the pi1541 which is another project). Then the Commodore 128 which I serviced, but I guess I have no post on servicing it. I’m still debating painting it, I won’t be retrobrighting it.

Finally the gamepad project, which I don’t have a post about. It is far from flawless, the Dpad isn’t great. It has 2 buttons, the normal fire button on the left and “button 2” is either “Up” or wired to one of the Pot inputs. It also has an adjustable speed 555 based Rapid Fire option for the primary Fire button. I want to revisit that project, maybe then I’ll make a post about it.

I made up some labels for the two units I built up. Below you will see the original 2019 prototype with the new 2023 label. I made that label the same way as before. It was printed on plain inkjet paper. Then covered with adhesive laminate film and cut to size. In 2019 I masked off the “case” and sprayed adhesive spray onto the case. I then removed the masking and put the label on it. This time I tried the “easy way” of spraying the paper, as you can see it ended up with the obvious effect of the paper looking like it got something on it showing through. That is why I had originally sprayed the Case instead of the label. This was for testing, and I wasn’t completely happy with the label. I need to get new ink cartridges for my printer and then I may remake the label. The second picture shows the reduced build CGA Adapter’s label. This label was printed on a scrap of HP Adhesive Vinyl. The printer didn’t print quite right due to being out of black ink and the red cutting out too. This label does look better overall although it isn’t perfect. I did put a label for Audio In on the CGA label. It is possible to jumper across the outer two pins of the Audio Out jumper to send the “Audio Output” jack to the “Audio In” Pin on the HD15 port for use with the SCART to HDMI Adapter. All I would have to do is open the case and cut in a hole for the rca jack and install it to the board in the future if I wanted to. I don’t plan to do that currently though.

I think that pretty much wraps up this project. You can see the label on the box there now, and the 128 is running JiffyDOS now. I do have the SID Audio, Monochrome 80 Column Composite, 40 Column SVideo, and of course the RGB through the GBS Control into on the Samsung TV.

NABU PC Black Screen, FAN Repair and Checks

Like a lot of other people I purchased one of the NABU Personal Computers that came up for sale in November. My Nabu arrived in December. It all looked good, when I turned it on there were two problems, the fan was making an awful noise and while I was getting a video signal it was a blank black screen. I opened the cover to look if something was out of place, and to check that fan. I pressed all the socketed ICs, reseated cables, tried other displays. Nothing helped and I didn’t feel it was worth shipping back. I mean even if scrapped I expect the computer was worth keeping.

I did inform the seller and he offered to send me another if I shipped it back. I decided to keep it in hopes of getting a second one, but there were none for sale. I kept looking back and recently he had some listed without the keyboard. I figured I probably had a working keyboard so I purchased a second one.

The new one came in and it worked with my monitor just fine. I was initially happy that the fan wasn’t making any noise, then I realized it wasn’t turning at all. I could hear that high pitch sound that likely indicated a stuck motor, which after opening it I found that was what was going on. We will get back to that later.

Now that I had a working Nabu I decided I would look at the other unit. The fan was noisy and I had pulled it back in December to check it. I connected it up to the monitor to see if it was in the same condition. It was still just displaying a black screen (it was powering on, and there was video signal), I didn’t realize it but looking at the LEDs on the front may have indicated if it was doing anything. Interestingly the fan was working much better, again I will get back to that later.

I found a guide to help trouble shoot the Nabu here: https://github.com/RudyRetroIntel/Vintage-Computer-Diagnostics

I have worked on a number of 80s era computers so there were a few things I was going to try. I started by pulling the power supply to get the fan detached to check it further. While I had the supply out, I checked it and reflowed some solder points on it. I didn’t see any issues with the power supply soldering, except I felt some pins were a little light on solder. I also polished all the connector pins on the power supply. They were pretty clean, but it was easy to do while it was out. I put the supply back in without the fan attached just for testing.

I pulled the mother board to get full access to it, and check the bodge wires on the bottom against the guide. It is the same revision of the board as in the guide, and has the same wires on the bottom (except different colors).

While I had it out I really don’t like that the LED board doesn’t have a connector on it. I put on a regular pin header and made a cable up and soldered that to the LED board and reinstalled it. Checking over the main board I didn’t find any issues. Before I reinstalled the mainboard though I rechecked the bodge wires, two of them had been pressed into and poked on component legs, I moved them and rechecked as I reinstalled the board.

I pulled all the socketed ICs starting with the video generator ic. That IC had very tarnished legs. I take it that is due to the type of coating on that chip, I see that type of tarnish on IC and connectors and such. I used a fiberglass brush on the legs being sure to also do the inside of the legs. The IC Sockets on the Nabu look nice, I put a bit of contact cleaner into the socket before putting the IC back. I did the same with all of the other socketed chips. The video generator was the only IC that looked questionable.

On the left you see the video generator chip before cleaning, then the right is the chip after cleaning it.

After cleaning the ICs and reinstalling the board the Nabu was working properly. The fan still needs to be reinstalled but it all seemed to be working otherwise. They were tested before shipping out, so I expect it was a bad connection on some chip, possibly that one above.

The next thing to do was fix the fans on both of the computers. I was thinking about why the fan seemed to be working well on the first Nabu as it wasn’t before I took it apart in December. I figured it just freed up. Then looking it, it was still rubbing slightly. I pulled the fan from the Second Nabu, it wasn’t turning at all. I found the blades rubbed the outer frame just at the bottom. Looking at it closer I could tell there was no gap in the bottom and a wider gap at the top. The fan comes apart by taking out three small screws, this separates the motor from the frame.

The fans are very heavy. They are made of cast aluminum apparently, both the frame and the blades. They have been sitting so long, it seems the fan motor settled a little bit and slid down where the blades are now catching on the frame part. To correct this, you just have to take the three small screws loose on the back and get it properly centered again and reinstall them. There is very little clearance on these old German made fans. Modern fans are all plastic and many have far larger gaps between the blades and the frames. After doing this process with both fans they are properly centered again and moving freely without noise or any catching on the frames.

I reinstalled the fan and added a connector so that I can easily put it out off I have to in the future.

These computers do not appear mass produced. There is hand done work with the various cables and connectors. There are odd choices in assembly. The fans only have 3 screws holding them in, there are washers on the screws, flat washers glued to both sides of the fans, those locking washers glued to the top of that flat washer on the inside and a nut glued to that (which the glue has failed from removing them). The LED board on the front has spacers between it and the front frame. The fan has one connector that is removable, but the other one had a permanent splice crimp on it so it couldn’t be fully disconnected. The oddity that is the power cable from the power supply to the mainboard, which has no connector on that end either. The LED board being permanently soldered to the mainboard. That LED board is difficult to remove having to bend one or more of the LEDs to the side to get it out, possibly due to the LED lead being left so long do to having to use those spacers. It feels like they were designed and had some issues that were addressed, it would have been cool to see a “Rev 2” Nabu without the little oddities. I like the system, it is just a bit odd.

I look forward to using the Nabu. I guess at some point I may look at coming up with a keyboard for the second unit. I really like the Nabu Keyboard. I keep realizing I probably should have more pictures of these things working.

PSU Bottom, Reinforced Ground connector on the lower right corner.

Both of the NABU Power Supply Ground Lugs pushed off the pcb when reinstalling the ground wire to them. The pcb is a single sided board and no through hole plating to keep it solid. The first one pushed and tore the copper the first time I went to put it back on, and I thought maybe it wasn’t solid or fully seated when it was put on originally. I pulled the power supply out and repair it, by soldering some heavy wire around the pads and adjacent pin to reinforce it. Then tonight when getting the fan reinstalled into the second NABU the same thing happened to it. I know that one was soldered on well, as I had reworked the solder points on it and had even added solder to them. I pulled it back out again and did the same reinforcement with some heavy coper wire around the solder points. The picture above the ground connector is on the other side of the board there on the lower right corner. The two points from the lug holes and the one hole to the left of it are now all joined up with the wire in the solder. I was careful reinstalling the ground wire so as to not tear it free again from the copper. With that fixed and the fan reinstalled both of my NABUs are working now. I do only have one Keyboard, I’m wondering what it would take to build up a replacement keyboard. I would love to have had keyboards for both, but the current listing for them doesn’t include keyboards. I don’t see myself using both at once, I hate to keep a fully working unit as a spare parts machine though..

The second NABU worked perfectly out of the box, it had some rust along bottom of the back edge of the case top. I cleaned that up scraping away the worst of the rust, then used a fiberglass pen to get most of the rest. I then put some clear nail polish to protect the metal a bit. Beyond that I fixed the fan as described above, as it didn’t spin at all. The fan is now removable as I replaced the permanent crimp connection on the one lead with a connector. The system looked good otherwise and is working fine. I didn’t do any other modifications or changes to it. That unit is back in it’s box sitting on the storage shelves.

The other unit which was the one giving a black screen before pulling and cleaning all the socketed chips, I also fixed the fan on. It is the unit I put the removable connector on the front LED Panel. This was the first NABU I purchased, and it is the one with the matching keyboard so it will be the one I keep out to use. It also now has the fan removable with the detachable connector on the second wire on it.

Commodore 128 80 Column RGBI/CGA to RGB Analog Adapter Part 3

Prototype v1.2 boards

The v1.2 boards arrived today. They look good, short of some labels having been reset shortly before making the order that I want to fix. The biggest being the Commodore AV Port header is unlabeled.

I checked placement of all the parts, and I found one issue. ( Thought I found an issue, but I figured out later that the unmodified RCA Jack does “just fit”, it is just quite tight.)

The RCA Jacks fit their footprint perfectly minus a bit of an issue with the back pin. These jacks are apparently intended to have the plastic pins on the front just sitting on the board. I put holes on the footprint to recess them in the board in hopes of a little more durability. The back pin won’t fit through the board.

With a quick touch up using the Dremel I made the Yellow jack fit nicely. I filed that little upper lip off. My intention was the alter the rca jack footprint to have a longer slotted hole in the next revision. Looking at it closer though and trying it, I can just get the pin to go into that footprint. It is snug, so I am planning on leaving the footprint as is. The jack doesn’t “have” to be filed down, but it is a bit fiddly to get in if you don’t.

I am making up two of the boards. The first one to replace my original adapter for the Commodore 128. That one will reuse the short Commodore AV Port DIN Cable and the short DB9 Cable from the original. The other board I am building up as a CGA adapter board, I am leaving off the Commodore AV Port parts (mostly) and adding the Barrel Jack for the 5V DC input. I don’t currently have any computers that use CGA, but I figured I have five boards and plenty of parts to put one together


The original adapter and the two new ones I am looking to assemble.

I salvaged the cables, ICs and one of the sockets from the original unit as I am scrapping it. I wouldn’t have messed with the IC Socket except I was practicing with my desoldering gun. It turns out I only ordered one VGA port, so I had to salvage one from an old monitor switcher board I have. I managed to get it off, and it is the same footprint as the new one. It wasn’t too easy, but went fine.

The two boards after soldering.

They turned out looking pretty good overall. The right board is the CGA board without the Commodore AV functions. It will take IBM CGA and a 5Volt DC Power adapter to make it into an Analog RGB signal with the CGA Brown Fix applied. That can go into a GBS Board, GBS Control modded board or something like a SCART to HDMI board. The primary limitation with the SCART to HDMI board (other than a lot of latency) is there would be no Audio on the SCART as CGA doesn’t have audio on the cable (for the Commodore 128 the Audio comes from the Commodore AV DIN Port). That and you need a Analog RGB to SCART cable, which my cable is a bit custom, see my cable pint out in the “original” project post from 2019.

The board is a perfect fit into the project box that I used for the original adapter. The openings are all different though, and you can just drop it in once the ports are soldered on. I guess you could “slot” in all the openings, but that leaves gaps from the top, which I don’t like. I plan to design a 3d printable case for the board. That is a part of the project that will have to wait until next weekend and likely longer though. I want to make it so it had all the required openings and is a simple split case that will fully enclose the board.

I do have to check that the boards are wired properly, mostly the Commodore 128 version with the cables. Then I will test the boards and see how it works. I will make the required corrections and changes on the pcb design and upload them to Github.

Above are some pictures of the testing. The Monochrome 80 Column pass through doesn’t work. I wasn’t thinking and passed it through the 74LS244 buffer, which it doesn’t work that way. The v1.3 board design no longer passes the Monochrome 80 Column video through the 74LS244. That is corrected on the v1.3 design I released on Github.

The rest of it works. RGBI works, 40 Column Commodore Composite pass through works. The 40 Column Commodore S-Video pass through and Audio via the RCA Port work properly. My Commodore 128 is being odd, I am not sure if it has something wrong with it, so it has limited my testing options. I did work on the C128 awhile ago, and it all appeared to be working except the cartridge port was being problematic. I haven’t been able to get it to work fully with the pi1541, although the 80column programs I tested are working through the pi1541. It may be because the pi1541 I am using is the 3A+, and the sdcard is setup for my 3B+ instead. I think there is a setting change required for timings.

The first image is through the GBS Control, with scan lines enabled. I have another post where I build GBS Control if you want to see that. The next being the adapter board connected up to the GBS Control. The second row starts with the SCART Converter to HDMI on the same color test. It is brighter due to no scan lines. Then the SCART Adapter connected up. The last picture was me testing an 80 column game using the GBS Control. I did find that the SCART Converter was not being stable when in a game though, it was flickering and blinking in and out. The GBS Control was stable on the same games. I am wondering if it is something with the sync signal. The one IC is a HC chip, which should be either an LS or HTC, that may be doing something to the signal that the SCART Adapter doesn’t like. I have another IC on the way. I’ll be testing the SCART to HDMI again when that comes in. I also did the bodge for the 80 Column Monochrome output and I will be testing that when I put the boards into their new 3d printed cases.

Part 1, Prototype Build: https://hobbytronics.home.blog/2019/10/08/commodore-128-80-column-rgbi-to-scart-to-hdmi/

Part 2, Board Design and Part List: https://hobbytronics.home.blog/2023/02/07/commodore-128-80-column-or-cga-rgbi-to-rgba-15khz-vga-adapter-part-2/

I sorted out the 80 Column Monochrome issues with the board and that is in as part of the v1.3 Release files posted in Part 4.

Part 4, 3d Printed Cases and links for the Released Files:


NABU RS422 Cable

I picked up one of the NABU Personal Computers, well two the first one was DOA for some reason. Shipping is prohibitive so I kept it for parts or repair. I just got the second one and it is working and displaying properly. To check it further and do anything useful with it I need to make up a cable for the RS422 to USB Adapter.

The adapter that is being recommended is a DTech USB to RS422/RS485 cable. I purchased mine from Amazon.


So the NABU has the 5Pin Din plug that needs wired up to the DB9 connection to the RS422 Adapter.

Cable Information from here: https://nabu.ca/nabu-internet-adapter-downloads

To make the cable we just require a 5 Pin DIN Male Plug, a DB9 Female connector (and Shell/Cover to make it pretty), and a 4 conductor piece of cable, it is recommended to use a Shielded cable though as well.

Just a note on the “*Note:” from the source page above, the NABU 5 Pin DIN Adapter port “Shield” is wired to the AC Line Earth Ground Pin. I tested my DTech RS422 adapter the DB9 connector is not wired to the Ground Pin on the connector or the USB Shield. The Grounding issues are either when there is “No Ground” causing the effect of having “No Shielding”, or if Both the USB and the NABU Earth Ground are wired together you get a Ground Loop issue. The recommendations are to keep the cable short, ground the cable shield to the Ground pin of the RS422’s DB9 port (Pin 5 on the DB9). I don’t know the merits of grounding to the Cable Shield to the DB9 Pin5 compared to wiring it to the NABU 5 Pin DIN Shield which goes to the Earth Ground pin on the AC Cord. I also don’t think the cable is required to be nearly as short as recommended. We aren’t talking about using faster than RS232 signaling and common cable lengths for such uses were 6′ or longer.

So now we have the parts collected, it is time to wire it up. Then Test the cable that it is wired to match the diagram above and that there are no shorts etc.

I ended up using part of a scrap of shielded cable I had which had enough wires in it. I cut the length of cable I wanted to use. I slid on the “boot/cover” of the DIN Connector, I expect that just about anyone who has made cables has forgotten that at least once. I then stripped back the outer jacket, took back the shield, I folded back the couple wires I didn’t need and put heat shrink over the ends of the cable to hold those wires back and give strain relief to the connectors of the cable. The Shield Wire is still there, I did connect it to the DIN end of the cable. I did not connect the DB9 shell to the cable shield.

They said to keep the cable short, I made mine longer than “recommended” but kept it fairly short. My RS422 adapter has a short usb lead so I wanted enough cable between it and this one to let me still reach a computer on either side of the NABU.

Above the finished cable with the RS422 cable connected. I tested the cable several times to ensure it was correct. I then loaded the adapter software on my laptop and tested it. It worked properly the first time. I used the drivers that were provided on the mini cd that cable with the cable for Windows.

I guess I could have taken a picture of the NABU online. Maybe I’ll add that to the post here later.

Commodore 128 80 Column RGBI/CGA to RGB Analog Adapter Part 2

This is a follow up to an older project I did. The RGBI (RGB Digital) to RGBA (RGB Analog) for the Commodore 128 80 Column Video. Commodore’s RGBI is essentially the same as CGA so the adapter works on either. I made my prototype adapter back in 2019. I wanted a project to work on and wanted to work with KiCad to see how that went.

The Original Project: https://hobbytronics.home.blog/2019/10/08/commodore-128-80-column-rgbi-to-scart-to-hdmi/

I had started making a PCB Design in Eagle back in 2019, but I never finished it. I didn’t want to keep using Eagle so I stopped working on it.

This project is the RGBI to RGBA project packaged into a custom PCB Design and with a few additions. Such as a dedicated 5V DC Power Jack for when using it with an IBM Based pc for CGA.

It still has all the Commodore functions and more passthrough functions now for the Commodore 128. The Commodore specific parts could be skipped though.

Below are some pictures of the PCB Design work in progress.

3/4/23 the finished v1.3. Is ready to download.

The board is sized to fit into the same case I used for the prototype. The problem with that is you can not get it into the case with the DB ports soldered on. I still laid it out for that size and the mounting holes to match that case. I have a couple of them yet. I think it would probably be better to design a 3d printed case. I can make it split at the place I need to get it in and out easily that way.

The board layout is basically a DB9 port on the left side for the RGBI/CGA input. Along the top the first port is for a single RCA Port for 80 Column Monochrome output from the Commodore 128’s RGBI Port. It is there, so I figured it is easy to include. You don’t need an “adapter” to use the Monochrome output, it is just Pin7 on the RGBI DB9 port on the back of the C128, I am passing it through the 74LS244 buffer though. The next footprint is a SVideo Port for from the Commodore 40 Column from the AV Port, including a 300 Ohm resistor on the Chroma line. The next port along the top is for another RCA Port and it is the Commodore 40 Column Composite Video from the AV Port. The last port along the top is a third RCA Port which is the Audio Output from the Commodore AV Port. There along the right side is the 15 Pin RGB Analog Output. The bottom left has the 5V DC Barrel Jack footprint (Center Positive). The Header pins are the C64 AV Port, it is oversized as I want to make it “keyed” with a missing pin and a plugged hole in the connector. The CSync/HSync is to set the Sync output for the normal HSync pin on the VGA port to either be Combined Sync (CSync) or to just pass through the HSync normally. The Audio header is a jumper to either output the Audio to the RCA Port above it when in the Left side or to output it on the VGA port on Pin10 for when I use it with the SCART to HDMI Converter box. InvertSync is another jumper to Invert the CSync/HSync line if needed. Finally the SCART Blanking is a jumper to enable sending VCC/5V to Pin9 on the VGA Port again this is for when I use the adapter with the SCART to HDMI Converter box, this enables the SCART RGB Detection on SCART Pin 16.

I think it is a reasonably sized board. If it was to be used for CGA with an IBM Computer then you can install the Power Jack, and omit the 3 RCA Ports, the Mini Din Svideo Port and the 10 Pin Header for the Commodore AV Port. If it is going to be used for a Commodore 128 RGBI, just build the whole thing minus the Power Jack. I think the only thing with the power Jack is that plugging it in while having the Commodore AV Port connected could end up very bad. I might think about that a bit more if the 3pin Barrel jack could be setup to bypass the AV Port power or something like that.

I did go with through hole for the ICs, headers and ports. I was thinking of going with dual footprints for the Resistors and Capacitors to allow either through hole or surface mount parts. The Surface Mount capacitors and Resistors are 0603 Imperial size parts. I have all the ICs already in DIP/DIL, and I want them in sockets for easy replacement if required.

I had to make the footprints for the RCA Jacks, and the SVideo Jack. The RCA Jacks should have square holes on the front corners. I couldn’t see how to make such cutouts. I figure that I may just have to shave the plastic a bit on the RCA Jacks.

The board as well as the original prototype build can do a combination of outputs depending on your needs.

The board in the fully configured mode outputs RGBS, Red, Green, Blue and Sync (CSync or Combined Sync) with custom Audio and SCART Blanking voltage on the HD15 port. This is what you use for a SCART Input. With the Audio to the RCA Port and the SCART Blanking disabled (may or may not be an issue if it is enabled) the GBS Control also takes RGBS input. The GBS Control might get confused due to VSync being included too on the HD15 all the time. With the SCART Cable the VSync pin is just not wired to anything.

If it is set to HSync with the jumper then it outputs RGBHV: Red, Green, Blue, HSync, and VSync. VSync is always on the HD15 port. The GBS Control takes RGBHV, and that is the setup I use with it.

It will also do RGBS with an Inverted Sync with the other jumper. I think did that variation because of something to do with the GBS boards at the time. I don’t remember what it was about though for sure.

The other two jumpers are specific for doing the RGBS with SCART, that puts Red, Green, Blue, Sync, Audio and 5V on the 15 Pin output. It is how I used this adapter until I build a GBS Control to go with it. The GBS boards weren’t as good for this use until the GBS Control project came out.

When using the adapter in RGBHV mode the 74LS86 is not required. The 74LS86 is just used to make the CSync by combining the HSync and VSync. It is also used to do the Inverted CSync if that is enabled (which it would also Invert the HSync technically if it was enabled while the other jumper was in the HSync position). If you look at the schematic you will see it is just bypassed. The 74LS244 is a buffer to protect the Computer video output. The 74LS138 handles the CGA Brown Fix.

I have received the parts I had on order and checked all the footprints. There was an issue with the DB9 port footprint that I had to fix. I also had a few adjustments to make to the Mini Din 4 for the SVideo port. I made changes for footprint corrections and some adjustments to labeling then put in an order for the v1.2 PCBs. I am going to build one to replace the one I made in 2019 for my Commodore 128 RGBI, as I want SVideo. I plan to scrap the prototype, reusing the short DB9 cable and the short Commodore AV Din cable I made for it. I also plan to build up a second one for IBM CGA without the Commodore AV Port related components. If the board tests out, I will post the KiCad project files and Gerber files on Github. Once I have the boards built up, I intend to design a case that can be 3d printed.

Update: 3/4/23 v1.3 I am correcting the schematic, the original one had the 80 Column Monochrome Video from the Commodore 128 RGBI port going through the 74LS244, and it shouldn’t be. I am also adding R11 as an option for a “Resistive Ground (RG)” on the Shell/Shield of the 15pin output port, it probably should have a 100 Ohm resistor between ground to help prevent potential Ground Loop issues. To prevent ground loops with the cable shield is generally recommended to only be “grounded” on one end, so you can put in the optional R11 or omit it. All of the other connectors have their shield to GND/Ground.

Parts List:

0603 – Resistors
1) 150 https://www.digikey.com/en/products/detail/walsin-technology-corporation/WR06X1500FTL/13239274
1) 300 https://www.digikey.com/en/products/detail/yageo/RC0603JR-07300RL/726765
2) 470 https://www.digikey.com/en/products/detail/walsin-technology-corporation/WR06X4700FTL/13240646
1) 560 https://www.digikey.com/en/products/detail/yageo/RC0603JR-07560RL/726805
3) 680 https://www.digikey.com/en/products/detail/walsin-technology-corporation/WR06X6800FTL/13240808
1) 1k https://www.digikey.com/en/products/detail/walsin-technology-corporation/WR06X102-JTL/13241138
1) 2k https://www.digikey.com/en/products/detail/yageo/RC0603JR-072KL/726726

0603 – Capacitor
3) .1uF 100nF https://www.digikey.com/en/products/detail/samsung-electro-mechanics/CL10B104KB8NNWC/3887593

RCA Jacks
1) Black RCA Jack https://www.digikey.com/en/products/detail/kycon-inc/KLPX-0848A-2-B/9990118
1) Red RCA Jack https://www.digikey.com/en/products/detail/kycon-inc/klpx-0848a-2-r/9990119
1) Yellow https://www.digikey.com/en/products/detail/kycon-inc/klpx-0848a-2-y/10246556

Svideo Jack
1) 4Pin Mini Din https://www.digikey.com/en/products/detail/kycon-inc/KMDGX-4S-BS/9990073

1) DB9 Male https://www.digikey.com/en/products/detail/amphenol-cs-fci/LD09P13A4GX00LF/4997285
1) DB HD15 https://www.digikey.com/en/products/detail/edac-inc/634-015-263-032/806194

1) 74LS244 https://www.digikey.com/en/products/detail/texas-instruments/SN74LS244N/277299
1) 74LS138 https://www.digikey.com/en/products/detail/texas-instruments/SN74LS138N/277285
1) 74LS86 https://www.digikey.com/en/products/detail/texas-instruments/SN74LS86AN/277315

Optionally a surface mount barrel power jack. Various pin headers and a couple jumpers.

See the next part of this project. Building, testing and fixes below:

Finished project: https://hobbytronics.home.blog/2023/03/12/commodore-128-rgbi-cga-to-analog-rgb-part-4-a-new-case/