Category: Retro Computers

Commodore 64 GAL PLA Replacement

Back in March, Adrian at Adrian’s Digital Basement posted a video (and a later follow up) on a cheap PLA replacement made with some still accessible GAL chips. When I saw it I picked up 5 of the required GAL chips. You need two chips to make a PLA replacement from them. The actual chips are GAL20V8B chips, preferably the -25LP but with an alternate programing of the one chip you can use the faster -15LP chips instead. The chips can be programmed by downloading the .jed files from the Daniel’s project website: https://www.freepascal.org/~daniel/c64pla/

While the GAL20V8B chips are no longer manufactured, they are in Daniel’s words still rather easy to get and cheap. The chips are able to be programmed in the popular TL866 programmers. I have the newer TL866ii Plus that I purchased for programming EPROMs. There are the older TL866 programmers and those work too, which is why he choose that model of chip rather than a similar still in production chip. This indicates that if someone wanted to they could likely recreate this project with that still in production chip at some point, but unless there is a shortage on these chips I doubt it will happen.

I happen to look around for parts and projects, so I had the chips laying around, but I have never pulled the trigger and ordered any manufactured PCBs from any of the providers out there. If you read my other posts you will see I have designed a couple of my own and etched them at home. That is a lot of work. These premade designs are not meant for that level of prototype work, the tolerances are too tight for me to make the way I made my other ones. Double sided and very small traces, a lot of through holes that need plated etc.. My one design being a single sided board, with wider gaps on the traces, also the lack of solder mask. The other design being wider gaps yet between traces to help with the lack of solder mask and it is difficult to manually align both sides and get them transferred to the board properly. I also designed my double sided board specifically to having to use vias between the sides.

So, how did I come about making progress after eight months? Well in looking for some parts for my TI99/4a, I found the PCBs for the GAL PLA for sale at what I felt was a reasonable price and ordered two. It turned out to be a very easy project. Since it is a manufactured board, all it really amounted to was installing the pin headers for everything. Adrian used Machined Sockets for the GALs and Machined Pin headers for the legs, in my case I used Machined Pin Headers for everything. Beyond that I did the same thing as he had.

Keep in mind what order you want to solder the headers up. If you use sockets, then you must put the underside legs on first. If you use all Pin Headers like I did, I found it easiest to put on the inner pin headers for the GALs on the top side, then the lower “legs” and finished up with the outer pin headers for the GALs. It turned out great. I certainly do NOT recommend using the larger square pin headers.. They damage sockets badly as they are far to large. The “turned pin”/”machine/machined pin” headers can be problematic as well especially in old single wipe sockets.

The Left are “square” pin headers like on Arduino boards, rpi etc. The right though is the machined pin headers

Above you can see the more popular Square Pin Headers. Those are not what should be used for the legs, you should use the Machined Pins instead. These are for the legs, the shorter pins going into the circuit board and soldered on there. The longer legs sticking down and those insert in the IC Sockets on the mainboard.

Machine Pin Sockets. I used these instead of IC Sockets for the GAL chips to insert into.

Above are the Machine Pin Sockets that I used in place of standard IC Sockets. I generally prefer Machine Pin Sockets to the single or double wipe standard ones. They machine type sockets are more flexible than standard sockets as they don’t go all the way into the PCB. These Machine Pin Headers though are almost identical to the Machine Pin IC Sockets, but can be made any required length. I didn’t have sockets of the size of these GAL chips, so I used the header strips. I also used these for the ATMEGA in my Pi1541, as I needed a Machine Pin Socket and the standard double wipe socket wouldn’t work on my homemade pcb.

The bottom with the round Machine Pin Headers.

A side note on the Machine Pin Headers and Machine Pin Sockets that I used. They fit together just like they are made for each other. With a little careful work and some heat shrink on the ends you can make them into inline connections for wiring. Sometimes it is useful like when I make lighting in models and such. They fit fairly well, it is a little like using those DUPONT Male and Female cables that use the “square” pins as seen further above. I think these kind of click in a little more securely, they also make a shorter connector in the end.

Unfortunately, before programing the GALs, I tried to program an EPROM for a cartridge I had assembled. A bit over half way through programming the EPROM the programmer failed, now it says it has a short of VCC problem, and fails the self test on the first VCC test.. That meant I had to order a new TL866ii Plus and wait on it to come in. I wasn’t very happy as I did not get very much use out of the first one even though I had it about a year and a half. I tried downloading the new software and putting on the lasted firmware, but the same result.. I have mostly given up on that programmer, but I certainly will keep it around incase I have an issue with the new one, or find a solution on repairing it.

The new programmer arrived the other day, and since I had the latest software and all the files already, it didn’t take long to program up the GALs. Still out of the 5 GALs two of them didn’t want to program successfully. I did program a pair then used the fifth one to start another set. I cleaned the legs on one of the two that didn’t want to program initially and it seemed to program properly that time around. I should have the chips ready to go for a second replacement if I need it in the future. I haven’t tried cleaning the other GAL and programming it again, I can’t do anything with just 1 GAL anyway at this point, but I did keep it incase I can get it working. I generally don’t do much during the week as far as pulling the Commodore apart, so I didn’t test it until today.

GAL PLA Replacement installed. I like Sharpie Oil Paint Markers for marking stuff like this. Standard Sharpie fades or rubs off over time..

Here it is installed in one of my Commodore 64s. If you read my other posts on this one where I cleaned up and repaired it, you may know I have a PLAnkton PLA in it normally. I am just testing this one. The board has a Machined Socket installed in it already which properly accepts the Machined Pin Headers, which the PLAnkton also uses. The PLA in my other Commodore 64 is also socketed, but it has a the factory single wipe socket. Installing the round Machined Pin Headers into that may damage the socket which wasn’t a great quality when it was new 40 years ago. That Commodore 64 still has an original working PLA in it, if I damage the socket it may not make good contact. If the PLA had failed, I wouldn’t be so concerned. In this case I am just testing that it works, so I know it is ready to go if needed. I doubt the PLAnkton will fail me anytime soon, but the factory PLA in the other 64 may.

I also have an ARM SID in this Commodore, I found the SID that was in this one had an issue. It may have been damaged all along, or it may have been when some traces were shorted by the unclipped legs on it.. The original SID was directly installed into the mainboard, and the legs were never trimmed at the factory. That left them sticking through quite a bit, and having the board sitting on the workbench ended up folding them over onto traces, and cut into the solder mask causing a short. The ARM SID wasn’t cheap, but I felt it was the best replacement if I wanted full function SID in the board. I am quite happy with it, but I do need to get the firmware update installed which fixes some issues.

I did not do exhaustive testing of the GAL PLA, but I did some testing here with the Dead Test and a short run of the Diag cartridge without the harness before that. I let the Dead Test run 8 full cycles without any issues.

I certainly like how easy this worked out. It looks well modified, but fits very well and is nicely built. I don’t have Super Zaxxon or anything to really stress this out that I know of. I have reinstalled my PLAnkton and closed the ole girl up. The GAL PLA is going to be packed safely in some EDS conductive foam for a rainy day.

Below is a link for Adrian’s first video on the GAL PLA. He did a follow up testing the Epyx Fast load as well.

Thanks for reading. I hope something here is helpful. I do most of these posts to kind of pull together different sources and include little things that I came across in doing these projects that may not have been mentioned in the other source material that I had when doing the project. This was a quick and easy project even though I kind of started thinking about it quite a while ago.

Due to getting these boards in and a couple others, I have finally made a customized board that I have ordered from JLCPCB. I know I see a lot more advertisements for PCBWay. Maybe I would try them at some point. JLC seemed more strait forward to get the initial order in and seemed a bit cheaper. Provided those boards work out, I expect that I will be putting together a post on that project after they come in. I have worked on a few things that I haven’t gotten around to posting. Mostly simple stuff that doesn’t take much in the way of a post and may not be of much value to post.

In the end I really don’t like waiting on things, or I may have ordered some of these PCBs myself. Then of course I waited 9 months to find some that someone else went to the trouble to order…. It really showed me how easy it is to put together a simple project like this when you have a properly made PCB compared to trying to wire up some sort of adapter from Pin Headers or IC Sockets and jumper wires. My Pi1541 was very time consuming to build. Sure there was a good bit of planning and construction, but had I ordered in the PCB, it would have been so much easier to assemble. It would have also been a bit easier to design the board when I didn’t have to take into account making VIAs by hand, dealing with lack of solder mask etc.. The Pi1541/Tapuino board did initially have a number of mistakes, and that would have kind of sucked to have ordered in and have to fix that, but it would have been possible. The board is kind of specific too, I didn’t want 4-9 laying around forever.. How many people want a Pi1541 the size of an original 1541 anyways? If I were to redo the project and it turned out possible to design it to be the proper layout and size to be a Pi Hat type but fit the original 1541, as well as maybe a break away Tapuino board section that could be stand alone.. I may have seen a use for more of the boards. That was far beyond ever doing with my hobby level board etching ability. I have since made a second Pi1541 (without a Tapuino), that one was a lot of hand wiring and would have been so much easier with a PCB or two.. Still what am I going to do with 5-10 of a board.. Most of my projects I only need one or two of.

Samsung 940MW TV Fix No Power

I recently picked up this old Samsung SyncMaster LCD TV. With my Retro Computer and Electronics hobby I felt it was worth trying to get working again. It had a paper on saying that it didn’t work, but I tried it anyways and it wouldn’t power on at all. I had come across that it can be possible to fix old lcds due to bad capacitors. I figured it was worth a shot so I brought it home.

The positive to this tv is that it has about any video hookup I may want.

Composite and S Video, and Headphone output. I have the cover plate off but I have it.
DVI, VGA with Audio in, EXT (RGB) on a SCART connector in the US?, And component, some Antennna thing..

The SCART really interested me as I have made the RGBI to RGB Converter for my Commodore 128 that I setup to use with a SCART to HDMI box. I will possibly be able to connect directly from my RGB unit with the SCART cable I already created. I am not familiar with the Antenna hookup on this TV though, I was initially going to first test this with my Timex Sinclair 1000 as it is an Analog TV, but I don’t have a connector for that port.

So the initial power on test had done nothing already (days ago so yes if it was just powered on the capacitors lkely have a charge and well it can be dangerous to open then). This is also not an LED backlight so it has a High Voltage section in the power supply to power the backlights, so be careful… So I started by opening up the case to see what I would find.

Bad Capacitors on the Power Supply Board.

Looking at it I saw 3 obviously bulged capacitors on the power supply board. I looked at the other capacitors and didn’t see any that were an obvious problem. I looked at the control board with it’s surface mount caps all looking fine. I then pulled the board and desoldered the old capacitors. I pulled the 4th one there that was the 820 like the one bulged one as it was suspect because the other one was. I also pulled the next closest one there to the right to check it out.

Yep Bad.

The 3 bulged ones were bad as well as the other 820 there even though it had not bulged. That fifth one off to the right tested out fine. So I went looking for replacements online, I can get them, and get them rather reasonably from the looks of it. Certainly worth investing in a screen didn’t have anything tied up in.

Still I didn’t want to go spending money on them and have them come in and it not work. So I dug through my spare parts. I found 2 exact replacement 1000uF 10v 105 degree ones. The other two the 820uF 25v ones I didn’t have. Now those two are in parallel, and this was just to test if they were why the TV wouldn’t work, so I went with a single 2200uF 25v capacitor. I don’t recommend it, while it may be just fine even in the long run, this was just to see if it would get the TV working.

Temporary Fix

So I thought, lets close this for safety 🙂

A little bit didn’t fit 🙂

So I turned it over and plugged it in. As soon as it was plugged in, the power light blinked. I powered it on and it went right to the no longer broad cast Analog TV tuner. Oddly no audio though, I expected to hear static. I couldn’t change the Source either to any of the ports. So I hooked up a Commodore 64 to see what would happen. Below you can see the results.

Success 🙂

As soon as I turned on the Commodore 64 I was able to change to the AV Source and it worked fine, the audio was there as well. I still have my S Video cable only at my one desk. I did see what looked like artifacts on the graphics around the shock towers (or what ever those are on the screen upper left). I need to make up a second SVideo cable for my Commodores. I did recently get one in that I want to add to my RGBI to RGB converter for my Commodore 128 80 Column mode.

Now I just need to get in the 820uF capacitors, well I will get a few of the others as well as I don’t know if they will hold up very well and I have to make an order anyways. Just a bit of cleanup and it should be good to go then. I look forward to trying out the SVideo input and seeing if it looks any less artifact like around those towers. I also look forward to seeing if the SCART connector will work with my Commodore 128’s RGBI output for the 80 Column mode.

The new capacitors came in. Below I have marked the ones I replaced. I picked up most of the ones Jameco had available.

So what did I find with them. Well originally those four main ones in the middle there were bad, with the 3 bulged and the 1 that was not bulged. Those were just junk.

The remaining ones I replaced were probably fine. I replaced that one off to the left, as it looked to be the same manufacture as two that had failed. It looked to be perfectly fine. The others that were replaced appeared to be fine as well. I was in there, I had them and I didn’t care to just put the old ones back in.

I did have to substitute some values. The 820uF capacitor value wasn’t available. There were 2 in parallel, so they add up to 1640uF. I ended up replacing them with a 680uF in parallel with a 1000uF to give a capacitance of 1680uF. My understanding is they should preform the same as the 820s would have been. The last three that I replaced were some 330uF capacitors, they checked out fine.

Some Testing with my C64 Mini. The TV doesn’t have HDMI, so I used an adapter to VGA in this case and also connected it to my 12″ bench monitor to compare the output. It works great with that adapter to VGA, but when I tried the DVI port, the image was going off the screen and only washed out and purple looking. I think it may be the adapter box as everything else appears fine. Last night I connected it up to one of my real Commodore 64s via Svideo, and it worked, but was washed out. The cable didn’t have a resistor on it, so that may have been why, I am going to make a second SVideo cable for the Commodore 64 and try it with the resistor on the line there.

I also tested it out with my Composite modded Timex Sinclair 1000 (US Model ZX81) (mod information on another post here). The results were very good. I am quite happy with it. I hope to be able to use this TV for a number of older computers and systems with the connections it has available on it. It is a lot more portable and compact than my Sony 19″ PVM that I have yet to find or build a desk to get it setup.

I decided to hookup my Commodore 128 to the TV as well to test it out. There was some disappointment in that this TV has a SCART connector, and I had made a RGBI to SCART converter that I connect to a SCART to HDMI adapter for using the 80 Column mode (See my other post on that). I was hoping that I could just no use the SCART to HDMI unit and go directly to the SCART input of the TV. Unfortunately the TV doesn’t see the input on the SCART port. This TV detects if a signal is present and then “allows” you to change to that port, if it doesn’t see on you can’t even select the port with the Source or Menu options. So I hooked up the Composite 40 Column mode to the Composite input and used the SCART to HDMI box (with a HDMI to VGA adapter yet) to connect to the RGBI 80 Column mode. The RGBI looks quite good even after all of the conversion. The Composite is not to bad. I do want to see about getting a good picture on the SVideo though. I am going to modify my RGBI to to SCART converter box to break out the SVideo signal as well, as it currently only has a pass through for the Composite video for the C64/40 Column output.

  • RGBI to SCART to HDMI to VGA..
  • 40 Column Composite
  • Yellow 128

Timex Sinclair 1000 Part 2: Recap and 16k Internal Ram

If you haven’t seen it, you may want to check the Part 1 Post about some other updates to this system: https://hobbytronics.home.blog/2019/12/15/timex-sinclair-1000-part-1-multi-region-composite-mod/

Today my order from Jameco came in. Part of that order included replacement capacitors for the Electrolytic Capacitors in the Timex Sinclair 1000. There are only two in the computer a 22uF 16Volt and a 1uF 16Volt capacitor. I ordered the closest replacements that Jameco had, which was a 22uF 25Volt Aluminum Electrolytic, and a 1uF 25Volt Tantalum Capacitor (which btw are also a form of Electrolytic Capacitor, polarity does matter). They didn’t have a 1uF in an Aluminum Electrolytic, but they had the Tantalum which is a valid replacement for it. We specifically want to maintain the microfarad (uF) value, but a higher voltage rating is ok, try to keep it close as it does have an impact if it gets to far away from the original. The higher the voltage rating the larger the capacitor as well typically. With other suppliers you can find exact replacements, but I was placing an order with Jameco anyways, and I haven’t ordered from larger shops and also didn’t want the cheap china capacitors. I don’t know for sure Jameco’s are much better, but I hope so.

Replacement Capacitors

There is a difference with Tantalum capacitors in while they are Electrolytic capacitors and polarlized, the positive side is what is marked. Where with aluminum electrolytic capacitors the negative is marked. Keep that in mind if you go to swap them. They are more expensive, but I only needed 1 and it wasn’t a big deal.

Before I switched them out. You can see the two light blue caps there on the board.
Here are the new capacitors installed.

So I fitted in the new capacitors. With the Tantalum I decided to insulate the one lead there, the positive one in this case. So I used some red wire insulation on it. If you look a these boards, the capacitor pads are doubled, as in there are a few closer points and wider points. The original 1uF was a radial capacitor, so it had long leads like the Tantalum as well, but you can see further to the right the “white” line there with a solder point and a “+” which is the solder point that would be used if it was an axial electrolytic like the 22uF is.

I tested the new and the original capacitors. The 1uF 16Volt came back with 1.114uF 1.1% voltage loss and 2.2 Ohm ESR. The replacement was 1.045uF .2% voltage loss and 2.5 Ohm ESR, so the old one was pretty close to the replacement values. The 22uF 16Volt was a bit different. The old one was 34.1uF 10% voltage loss and 15 Ohms ESR, while the replacement is 20.8uF .9% voltage loss and 0.86 Ohms ESR. I don’t know exactly what I should expect, but my thought is that the 22uF appears to be getting out of specification pretty well.

Once I had the new capacitors installed I did test that the computer booted, which it did. I then moved on to the 16k internal ram upgrade, as my 16k Ram expansion does not work, and it is an easy modification to do internally.

To do the ram upgrade I used Tynemouth Software’s guide found here: http://blog.tynemouthsoftware.co.uk/2017/10/zx81-internal-16k-ram-reversible-version.html

GadgetUK164 did the upgrade on a video here: https://www.youtube.com/watch?v=14eL_oWhhXo

With the Timex Sinclair 1000 it is very easy, the computer came with a 2k ram chip already installed in a ram socket. That means I just needed to get a 62256 ram chip which is 32k, but I will only be using 16k of it, and run 4 wires.

2k Ram in the socket

You can see the original ram is in the socket, but it does not fill the socket, and is actually not even installed in Pin 1. I am sure many or even most ZX81 computers do not have any socket or may have the smaller footprint socket in place. GadgetUK164’s ZX81 had the two small ram sockets installed on his board, he used some header pins so that he could leave the original smaller socket under the larger ram chip. There may be some that have a smaller socket as well that is missing the top 4 pins, which could be removed and replaced with the full length one, or just clip the pins from another socket or use some header pins like GadgetUK had to extend the socket.

So that I didn’t have to damage the circuit board, I straitened the required pins on the new ram chip.

Pin 1, 21, 23, and 26 with the wires.

Next I pulled the 2k ram chip and installed the new chip. The 4 lifted pins are bent up so they won’t make contact with the socket pins.

installed

Above you can see the chip inserted and wired to the board. The wires are attached at D1, D2, D3 and D5 (yes we skip D4). Tynemouth mentions the order doesn’t matter, but they are in that order to be the easiest runs. I used some 30awg solid core wire for this, which also happened to come from Jameco today. I figured it was a pretty color and they are all datalines. I just tacked them to the diode leads. Tynemouth had desoldered the diodes and put the wires through the holes. Diodes don’t like a lot of heat, so soldering to them can risk breaking the diode, but desoldering then resoldering them can too.

Another view

The way I did it is not quite as pretty as Tynemouth’s example, but we are talking about a mod that includes straitening pins on an ic and having flying wires on them. He desoldered the diodes and put the wires through the holes with the diodes. Doing it the way he had ensures it won’t have a chance of the wires coming loose. I didn’t want to risk desoldering the diodes, I didn’t have a great desoldering iron, and these boards are delicate. I needed to be sure I had good contact, and not a bad solder joint that will fall off of the diode lead there and short to something else. I tinned the wires with solder before putting them to the diode, and added a dab of fresh solder and flux to the diode lead first. If it was corroded a bit the solder may not take, but it took very nicely and also adding that bit of solder does add some new flux to clean the point. I had my iron set on 300, which is what I typically use for board soldering. I also use leaded solder, which is what these old computers had to start with too.

The last bit I did to the Timex 1000 here was to add a heatsink to the ULA chip.

Finished

I have now finished the modifcations I had planed for this computer. I just need to wait for the thermal glue to dry on the heatsink before reassembly tomorrow night.

The next thing I need to do is reinstall it in the case. Then I will be testing the original keyboard to see if it is working properly as well as the computer itself. I hope to have this back together tomorrow night and see how it works out.

The Ram Upgrade works.

I got it put together and ran the check posted on the Tynemouth Software post. It shows 32k, but it is showing the 16k Rom plus the 16k Ram.

The keyboard tested good and is fully working. I had a problem with the PAL/NTSC switch (the old channel switch), was offset a bit to far to the edge of the board, and I could not get it set in the NTSC setting while inside the case. I had to heat the solder and push it to the one side to give it proper alignment in the case. The holes for the switch are very large, you can see that in my Part 1 post where I have the switch and the cleaned out holes. The switch now lines up perfectly and works as intended.

I found the heatsink on the voltage regulator had no heatsink compound on it at all. I removed it and added some silver thermal compound and reinstalled it.

After starting to put the system back together it wasn’t working properly. It was an issue with the ULA, if I bumped it then it would get flaky or work. I reseated the chip and then it was working again. I hope it continues to work. I did find someone has made modern replacement ULA chips, hopefully this one will be fine an I won’t have to get one. I have a Samsung LCD TV which I had been working to repair. I finally finished it last night and here is the Timex Sinclair 1000 Composite output on it. It looks very good. You can see it beside the C64 Mini there which I was also testing the TV repair with. They look kind of cute beside one another. You can find info about the TV repair in another post here.

Timex Sinclair 1000 Part 1: Multi Region Composite Mod

I recently picked up a Timex Sinclair 1000. I first tried connecting it to my LCD TV which does have an analog tuner, but I couldn’t get the signal on it. I then dug out my VCR from the storage area and connected to that. That worked just fine. I am not sure why the TV wouldn’t take it directly. The signal looked pretty good too. I really didn’t care to use the 1000 on the TV all the time though, and not with the VCR all the time either. I went on and looked into a Composite Video modification for it. The modification is done with the same little transistor circuit as the Atari 2600, which I have done before. This is only when the system has the later ULA 2C210E chip such as mine, the earlier ULA 2C184E does not generate quite a standard video signal, so that requires a different circuit. I don’t know if any of the Timex models have the early ULA chip or not. The Timex Sinclair 1000 is a rebranded Sinclair ZX81. The RF Modulator is different for the US Timex model (and the US ZX81 which they did sell some of), there are a few other differences. The Timex 1000 came with 2k of ram rather than 1k like the ZX81 came with and outputs to 60hz NTSC video while the UK model does 50hz PAL video output.

I used Tynemouth Software instructions on the Composite Mod. Found here: http://blog.tynemouthsoftware.co.uk/2016/11/ts1000-multiregion-composite-video-mod.html

I used the stripboard circuit from TheFutureWas8bit Atari 2600 mod:

https://www.thefuturewas8bit.com/2600_comp_mod

I also used info from GadgetUK164’s video: https://youtu.be/5OQuJ-GMwF4

Although in his video he had the OLD ULA chip, and the simple Transistor circuit didn’t work properly for him, he went on to make the more complex circuit later on. His initial bit was using the transistor circuit such as I ended up with.

I found good schematics for the ZX81 here with other useful info. This is where I ended up getting information as to what the various extra Modulator connection labels were.

http://fetrmartin.free.fr/ZX81/

I would post the schematics and other bits from the sources, but that is their material, this is how I used their material, you would need to build the transistor circuit from TFW8bit, or you can buy the board they sell which would simplify matters.

I went with a little different approach than I initially intended. I was going to leave the RF Modulator in but disconnected, that didn’t work out. There wasn’t much room, and I couldn’t remove the capacitor and resistor(?) and wire from the RCA jack easily, and I couldn’t get the strip board to fit reasonably with the Modulator still in the box. In the end I removed the internals of the RF Modulator and installed the new circuit inside.

I want to note that with the ZX81 and the US Timex 1000 (and I guess the ZX81 US kit), the pins used for the RF Modulator are different. It uses the “USA” marked pins, it uses 3 of them.

For the US model, it uses 3 wires instead of 2 for the UK versions. USA3 (Not FR3) is the far left wire, that is apparently the Video in signal although I don’t know where it comes from exactly, as that is not the direct pin from the ULA video output. The next USA2 is actually +5Volts. Then USA1 is the last and it goes down to the Channel 2/3 switch. That switch actually switches between Ground and +5Volts ( I use that later as Tynemouth did).

For the Composite signals, I actually removed the RF Modulator board etc:

Modulator bits, the board, with the 3 wires, and the Capacitor and resistor, and the output wire on the right.

Here is the board installed, it is built as TFW8bit’s stripboard, although on a larger piece of board so it would stay solidly in the modulator box.

Composite Video circuit.
DIGITAL CAMERA
DIGITAL CAMERA
The Black is Ground and goes to FR3, Orange is going to UK2 that goes to the ULA video. Red is USA2 which is +5Volts

Above you can see the wires used. Originally the modulator of course used USA3, USA2, and USA1. In this case I am only using USA2, which is now the third wire not the middle one going in. The first is going to FR3, which is actually Ground, yes the modulator chassis is ground as well, but I didn’t care to solder to it, and had the opening for the third wire. The middle wire goes to UK2 which is the video directly from the ULA chip pin, and not the round about way that USA3 apparently gets it.

First I tested this out and it worked great. Here it is via the Composite input on my little LCD monitor I keep on my bench.

Success.

There is a second modification though. The channel switch is no longer needed, and it can be re-purposed for something else. Tynemouth used it as a NTSC/PAL switch, which is a simple change. This involves R30, which goes to the one pin on the ULA, and to ground. It is a 10 ohm resistor that when pulling that pin to ground causes the system to operate in NTSC 60hz video mode. When it is disconnected from ground the ULA sets the system to run in PAL 50hz mode. To do this I reused “USA1” which goes to the switch center pin already.

USA1 ready to use.
The Grounded side of R30 lifted from the board.
R30 wired back in
USA1 used
Heatshrink insulation
R30 now going to USA1, the exposed lead is covered with clear heatshrink tubing.

Next the Switch needs a bit of a change. As I mentioned earlier the switch changes USA1 from Ground and +5Volts. We don’t want to wire R30 to +5Volts. To do this you could remove pad from the circuit board, or you could trim the wire from the switch and ensure it was insulated. I didn’t want to alter the board, so I altered the switch.

Original
Pin removed
Insulated with liquid Electrical Tape

Next I installed the switch and tested it. Be aware, I made a mistake installing the switch..

Switch to the Right “PAL” (Switch installed on the wrong side of the board… see below)
Video output, PAL
Set to PAL 50hz mode.
Switch to the Left “NTSC” (Yes the switch is still on the wrong side of the PCB.. see below)
Video output, NTSC
Set to NTSC 60hz mode.

So, some may notice I installed the switch to the wrong side of the board. So this won’t work in the case now. I realized this shortly after putting all of the tools away, but before I was going to reinstall the board.. So I desoldered the switch again and installed it to the bottom of the board like it should be. When I put the switch on, I reinstalled the old paper label they used to insulate it, and to beef it up a bit, and cover the hole from the old pin that went into the +5Volt pad, I put a little piece of Kapton Tape, you can’t see the tape in the photos though as it is under the original paper label.

Switch installed properly..

I then retested it. I have another bit I am looking to do with this board and that is to put in a 16k ram upgrade on board based on Tynemouth’s post on it, and that again GadgetUK has done a video on. It really is not going to be anything new, while the Composite mod, I did a little differently.

I haven’t tested the keyboard on this unit, I did order in a replacement keyboard for it, and if I don’t need it I will keep the original on it for now.

To finalize the upgrades, I have used a little Brother Label maker to update the Labeling on the case. They are stickers so it can easily be removed. They stick very well, so they should hold up fine. For this one I purchased some White on Black Background labels. I use these labels for various projects, and have been using them for years with good success. (Note: be careful with leaving batteries in these Brother Labelers, they drain batteries when off apparently and then the batteries leak. I have had it happen to the labeler at work, and my personal one here at home.)

Stock Channel 2 – 3
50 PAL/ 60 NTSC Label
Stock markings
Composite and 50/60 Labels

The computer did come with the 16k Ram Expansion, but the expansion doesn’t work. So there is a Part 2 Post where I install 16k Ram Internally on this computer. I had looked at repairing the 16k Ram Expansion, and the one capacitor was bad on it, but replacing that did not correct the problem. They are rather complex boards, and while I wouldn’t mind repairing it, I am was not sure where to start. I thought of stripping out the 74 logic chips to test and such, but that is about all I could do. The internal 16k ram upgrade is quite easy though with the right ram chip and a few wires. It is also cheaper to source that one (32k which we only use half of) ram chip than the very specific odd chips in the ram expansion. I don’t have to damage the mainboard or anything to do the ram upgrade it is fully reversable. I mostly have to swap the onboard ram socket and do the few wires onto the new chip.

Update on the 16k Ram Expansion: I did end up getting a RAM Tester in early 2023. I pulled all of the the Ram ICs from the 16k Expansion, half of the ram chips had failed, maybe when that cap failed it made a surge? Or it lost the 12V power and that burned those out running without it? The 74 Logic ics were all good. I will not be repairing the Ram Expansion as I don’t need it and can not use it. I did fully strip the PCBs of ics to test them, I don’t know if there would be some project I may reuse it for in the future. I did damage one trace but it is repairable and could easily be rebuilt if I wanted to.

Pi1541 in 1541 Case & Tapuino – Part 3 : Schematics and a bit

I wanted to post the final Schematics for the Pi1541 Option B+SRQ and Bare Tapuino here.

Gerber Files for the board can be downloaded from here:

https://github.com/Markeno76/CommodorePiTap

Below is the Bare Tapuino schematic. It is basically a Tapuino using a bare ATMEGA328 instead of an Arduino Nano etc as the base. The ATMEGA is burned with the Arduino Uno boot loader. It can be programmed by pulling it or on the board. The required connections are available on the board by the Reset pin plus and other headers. That is why the Reset pin is there, to make that easier. I didn’t route a regular ICSP header though. It was hard enough to route this board for me, and I believe the other header with the required pins would have had to been unplugged for it to succeed. There has not been any firmware update for the Tapuino in a good while either. The design is a combination of the schematics from the Tapuino Github. The C2CON header is for the secondary Cassette for recording from it. I did not use that, although I do have the header in there on my board I have no connector anywhere to accomplish it. Because I am not using that feature, I really don’t need the 4052N on my board. That is what it is for. The 4052N can be bypassed by putting two jumpers in its place. The first jumper goes from Pin1 to Pin3 on it (Write Signal). The second bypass jumper goes from Pin12 to Pin13 (Read Signal). The Tapuino is a Tapuino 1.5 plus the Read and Write LEDs from the Tapuino Mini 1.02, and then using a bare Atmega instead of a Arduino Nano or Mini etc. I could not find schematics for the later Tapuino versions, I guess someone else made them to sell and has not released them. I didn’t care for a buzzer or speaker attached to hear the playback, so I was fine without that. I really do not have the Read or Write LEDs on my board at this time as they were added later. I might add them, but I am not sure it is worth the trouble. I would have to take my control panel apart to get them installed, my thought is to place some surface mount LEDs just behind the mesh. The other thing I would like is there was another firmware out there that had some “graphical” look to the Tapuino LCD display, I would really prefer that. I can’t find it anywhere, it was posted on a German blog I believe, but only pictures of it, no code etc.

The other note on the 4052N is that the 74HTC4052N does not work, but a 74HC4052N does work on the Tapuino.

Being a “Bareduino” base, there are other components on the schematic that are not typically on a Tapuino. That is because most are based on using one of the Arduino boards as a base. It was a good excuse for me to make a Bareduino.. I figured why waste an Arduino Nano or something like that if I was making a board anyways.

Pi5141 Option B + SRQ and TFT LCD Passthrough header.

The above is the Pi1541 Schematic. It is Option B plus with the addition of including the SRQ signals. They will be required for some updates to the firmware to take advantage of.

The TFT LCD Passthrough is probably less useful to most, it is actually a traditional Mini Din PS/2 Port. That is what my little 7″ Composite LCD came with as a connector. I decided to put it into the Tapuino. It was originally for use on my workbench to test my Commodore 64. It supports 2 inputs, the default is the one connected to the Pi’s Composite video output. The second input is out the back of the 1541 case and can be connected to the Commodore 64 Composite Video output. The board footprint and setup is actually setup so as to allow putting a Second Serial Din port side by side with the first one. If that was the case, then the TFTLCD header would be wired over to the back of the Serial port and the Serial Din would be installed instead of the PS/2 style Mini Din.

The 7″ LCD though lets me use this device as a stand alone device with the Pi, or with the Commodore as a reasonably portable LCD. There is also a jack on the back of the 1541 for an Audio Input with a switch beside it. If the switch is flipped toward the jack it will output the audio from the external jack to the internal amp and speakers, if it is switched the away from it then the audio is connected to the Pi’s audio output instead. This lets me play the Pi sounds through the internal speakers. The speakers are actually Mono, the rear jack is mono too. The Pi audio output is mixed down to mono with a resistor to prevent them back feeding into each other and damaging the Pi’s audio output. The alternate is that I can again connect up the Commodore 64’s Audio Output to the internal speakers.

The MicroSD Cards are both accessible from the front, the one on the left being the Pi’s card slot, which is extended with a MicroSD extender. The one on the right being the Tapuino’s card. This lets me remove them to add or remove files easily. The other thing it allows me is to swap the card in the Pi. I can then use the Pi for more things like running Raspbian on it, I can then output that to the internal speaker and the 7″ LCD. It can alternately access the HDMI Port on the side of the case (again with an extension going to the Pi itself). I can also put in a card with RetroPi on it, which again can run on the internal speaker and 7″ LCD or alternately output through the HDMI. I can then connect up controllers to the USB ports that are accessible on the side as well.

DIGITAL CAMERA
Ports: Yellow Composite Input, Red Audio Input, Audio input switch (Left External, Right Pi Audio), PS/2 (TFT LCD Jack), Commodore Serial Port, Tapuino to Cassette (6pin Male). Then the original Power Switch, Power Cord and Fuse which are all still in use.

There are plenty of variations on the design possible. My point was to reuse this case I couldn’t otherwise make use of due to the failed read write head on the unit. The transformer I had left was for 220Volt input, so that wouldn’t have been of use to me either. I wanted to do something with it that would fit in with my C64, and there was just way to much extra space to not make more use of it. I liked the idea of doing a Bareduino project as well.

The Cassette cable worked out really well to. It is basically wired up as a passthrough Pin 1 to Pin 1 from the Din to the Card Edge connector. The Card Edge end is bolted into a DB15 (Gameport type not HD15 VGA (which is DB9 sized)) shell. I later painted it with a Green “Top” mark and lines and a Red “Bottom” mark so that I know which side should be up. I also inserted a bit of plastic to work as a Key into the slot in the connector. I had done that before and it fell out, so i wanted to have a visible mark as well. The wire is part of a very flexible Cat5 cable (yes old Cat5 not Cat5e) that I came across, I pulled out the extra 2 wires to make it more flexible as well. The ends have some heat shrink on them to build them up slightly and provide some strait relief.

Above you can see both the 7″ LCD and the little OLED on the drive face both display the Pi1541 output. So it can be used with or without the 7″ attached. The Pi controls are there on the left side, the 3 buttons and the 2 way momentary toggle switch. The Red LED is the Pi1541 activity light. The Green led on the left in the factory location is the Pi1541 power LED, it lets you know the Pi’s power is turned on. The other Green LED on the front panel is actually the Power LED for the internal audio amp. The Red tipped knob is the volume control and On/Off for the Audio Amp. The 4 buttons on the right are the Tapuino controls with the small LCD on the right being the Tapuino display. The Tapuino is powered completely by the Commodore 64 Cassette port. So the main power for the Pi does not need to be on for the Tapuino to work. That is partly why there are 2 schematics. There are two 5Volt power sources, the one that Pi uses is the internal Meanwell power supply where the Tapuino section receives the power it uses from the Cassette port, they are not wired together. They do share a common ground, which they share through Serial connection anyways.

I have used this unit for Raspbian as well as Retro Pie as well. My general intention is to use it just as a Pi1541 though most of the time. Originally I figured I would use it for Retro Pie a bit as well, but I have since built a Bartop Arcade to run Retro Pie instead. I really didn’t feel like disconnecting it from the Commodore desk and moving it to the living room to connect to the TV and such just to play some old games (other than Commodore games that is).

I have been thinking of putting a button on GPIO3 for a safe shutdown and startup button for the Pi when using Raspbian or Retropie like I did with my Bartop Arcade build. I just don’t at this time know where I would want to put the physical button. I could reuse one of the Pi1541 buttons, I could assign Safe Shutdown to another GPIO Pin that they happen to already be connected to. Still that would then not work as a wake up button as GPIO3 is the only one that will wake it.

Commodore 128 80 Column RGBI to SCART to HDMI.

I have been wanting to get a working display for the Commodore 128 80 Column mode. Looking into it, certainly get an old compatible CRT Monitor, either a Commodore RGBI monitor or apparently a CGA monitor potentially. Well they are old and they are expensive, and quite expensive to ship. There a couple more modern LCDs, including some NEC Multisync 70 series monitors. They are apparently around, but they are old and somewhat expensive too. If I get a display I would rather have confidence that it will last for a fair while. That and I am pretty cheap I guess.

I looked at options, the Monochrome Composite 80 Column mode is easy. Just make up a cable with the DB9 and a regular RCA plug on the other end. I want color though.

There are some CGA(RGBI) to VGA converters that people make to sell. They convert the Digital CGA signal to an Analog RGB signal, that is close to VGA. The frequency is at the CGA 15khz though instead of 31khz like VGA though. So most monitors don’t accept the 15khz signals (NEC Multisync 70 series is one of the few again, and the 60 series that I have doesn’t). Then you need a second unit that then takes that 15khz to a 31khz VGA signal.

I found a circuit design for a CGA/RGBI to Analog VGA. This is the first part, and you need a secondary converter to take the 15khz signal to the standard VGA 31khz. The GBS-8200 is a popular solution to take the signal to 15khz. I found another solution, which is a SCART to HDMI converter that Adrian Black posted about on his Youtube channel. I picked one up, an a donor cable to make up a proper cable for it.

I took the RGBI converter diagram and came up with a bit of a hybrid of it. I had tried an earlier wiring up to see if my Multisync 60 series monitor worked, it didn’t. So I am making up up circuit I found. There was a report by another site that said they didn’t like that circuit, and preferred another circuit for the process.

The draw back of these RGBI converters is that while they are full 16color output, they output Dark Yellow in place of Brown. It is not a fault of the circuit, it is because that is how CGA/RGBI worked, the Monitors actually handled the color replacement. To do the Dark Yellow to Brown replacement requires including the 74LS138N ic. When it gets the “Dark Yellow” signal, it injects just a little bit into the “Green” pushing the visual output from Dark Yellow to Brown through R1 below.

Update 2/5/23: Today I was looking to revise this project to a PCB Design. In looking at, it I and thought the Sync Invert was incorrect on the schematic. I was wrong, it was correct so I have switched the schematic back to the original from 2019. I have no promise I will complete a PCB design, but if I do I will be posting it up on Github or another site. I am thinking of making the pcb to fit into the same case I used for the prototype if possible. To make it more useful for IBM CGA I plan to put a power jack on it, the Commodore AV Port will be a pin header row or something, so it will be optional. There will be the optional Audio Jack coming from the Commodore AV Port, as well as an option for the Monochrome 80 Column Composite output (because I can), Commodore 40 Column Composite as well as Commodore 40 Column SVideo output. I am making the PCB Design in KiCad at this point. I want to see how that works. I had used Eagle back at the time of making this project initially. I have recently used EasyEDA as part of the Super Game Boy project, as Joe had build it in there. I wanted to see how KiCad compares. The schematic is nearly finished in KiCad, but the one in Eagle as seen below looks “neater”. I am finding some issues with KiCad not having footprints I would like to be ready to use, but we will see once I start having to work them out and find parts.

Progress on the 2023 PCB Design. See my other posts on the progress there. V1.3 files are now released, see “Part 4” post for the links.

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

https://hobbytronics.home.blog/2023/02/27/commodore-128-80-column-rgbi-cga-to-rgb-analog-adapter-part-3/

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

Here are some pictures of the unit built up on some protoboard and reusing a section of board with a HD15 VGA connector on it. There are a couple of things I will be doing with the board, first I will be installing a 150 Ohm resistor on the board (R9). Currently in the second picture you can see an old 150 Ohm resistor in there for testing. I was making sure that 150 Ohms wasn’t too much and that it brings the current usage down to what I consider should be a safer level. Initially I had been using a higher value resistor and the circuit wouldn’t work. The SCART box needs enough voltage on Pin16 “Blanking” which switches it over from Composite Video to RGB Video mode. With too low a resistor I wasn’t happy with the current draw. I am going to be powering this board from the Commodore 128’s AV Port. I didn’t want to risk damaging the computer by pulling to much power through the port. With the 150 Ohm it had lowered it to a better level. The other changes I will be making also involve the AV Port connector. I want to be able to connect up for both 80 and 40 Column video modes, with the AV Port plugged into the box for power, I can’t get to the 40 Column signals. I am going to add another RCA jack for the Composite Video, I will also add a SVideo port somehow later on, so that will be an option for 40 Column mode. The a RCA port was the Audio out coming in from the AV Port originally when the first pictures were taken (in the end I moved the Audio to the side, and made that port 40 Column Composite Video). The Audio also goes into the “vga” jack and is sent to the SCART converter to go into the HDMI signal from it. I could have hard wired in the SCART Cable instead of including the VGA port. I wanted to give myself other options with the box though. That is also why there are some jumpers on the schematic. They are there on the board, but they are not easy to see as they are a bit under the wires in the pictures below. The jumpers can allow to switch from Combined Sync mode (CSync), to the VGA Split Sync (HSync & VSync). The second Jumper is the Inverter jumper for CSync/HSync line, with it one way the CSync is inverted, with it the other way it is not inverted. This gives options to potentially connect to other devices, like the GBS8200, maybe some Multi Sync VGA monitor if I come across one. The only concern I have with either of them, is that I am sending Audio to the VGA port to Pin 4. If the Monitor or the GBS board do anything with Pin4 they could damage the SID or be damaged themselves. The other alteration on the VGA pin out is Pin 9 has the “Blanking” voltage wired into it, old VGA cards (very old I guess) sometimes had a 5Volt output on that pin, so as I am feeding it with something under 5Volts it shouldn’t do anything, but that doesn’t mean something won’t be wired to it. I have seen diagrams of people thinking Pin 9 on the VGA port should be Grounded, which that would be bad.. certainly it wouldn’t be a good thing to do.

So after a lot of checking of my wiring, I finally connected it up to the Commodore 128, and well it worked. That was great because I couldn’t get it to work 100% on the breadboard. I though the issue might be the variation of the XOR Gate IC I was using, so I had ordered in some replacements, so it was either that or all of the slop of the breadboard wiring. There is that “Saturn’s Rings” looking interference there going across centered around the Light Blue line. That was a visible thing on the display. I didn’t have that specific issue in the breadboard circuit. The point to point wiring isn’t the best either, so maybe that has something to do with it. I have yet to try it on another monitor though. Still I am pretty happy with it, and soon I will be able to close the box up and make use of the 80 Column mode when I want to. The color correction on the Brown seems to be working, the text at the top is in “brown”. At the least I can say it looks closer to Brown than Dark Yellow to me. The other colors look reasonable to me as well.

Success.

Below here is the SCART to HDMI Converter I am using. I found it on a video by Adrian Black where he was recommending this model specifically over the other similar priced models. He said that Heatsinks needed applied to the two chips inside though.

Below you can see the two heatsinks I installed. I hope they are enough, the little one in the lower right is fine, but the main chip heatsink is smaller than the one Adrian was using. I don’t know how hot these get with use. If they “sort of work” without them, I would hope that they will be just fine with these. They are the type that come with some 3m tape applied.

Two Heatsinks Installed for reliably.

Above I have put together a diagram of the Output of the circuit I built and how it is wired to the VGA port and then how that wires over to the SCART Cable. For a GBS8200 or proper Multi Sync VGA monitor you would just use a regular VGA Cable. I would feel better if you used a minimal VGA cable, which is R,G,B, Ground, C Sync/H Sync and V Sync. I find that the thin modern VGA cables now only have those wires in them. I have had older ones that were about as small but did have all of the wires in them. I am putting in a jumper to disconnect the Audio from the VGA port for safety. When the jumper is moved to the other position the audio then goes to the RCA port on the side (the Red one not the Yellow one).

Here is the Analog RGB side. The RCA port there is now wired to the
Commodore AV Port Composite Video (40 column output). I painted it yellow to reflect what it is.
Here is a top view once it was finished. The Additional RCA on the side is now wired to the Audio Out from the SID via the Commodore AV port and is Red to reflect it is an Audio port. Below you will see an additional “jumper” that is not on the schematic labeled “<Audio” that is a 2 position jumper that either passes the Audio to the “VGA” port or to the Red RCA Port depending on the position it is set to.
Above I put on text for the 4 jumper locations and functions. SCART blanking is connected or disonnected, Audio is to the VGA Pin4 or to the Side RCA. Then CSync Inverter or non inverting. Finally CSync or HSync (such as if I had a compatible MultiSync Vga Monitor)

I certainly look forward to using this setup for my Commodore 128. I added the label below, it is printed on an inkjet printer with standard paper. I then used some tape to mask off the top of the box, and sprayed it with Locktite Spray Adhesive 200 Middleweight bonding spray. I let it slightly dry before putting the paper inplace so that it would not bleed into the paper. It is sticking perfectly, I guess I will see how long it holds up. I may have put some clear packing tape over it before cutting it out, but I didn’t have any. I have used the process for some cartridge labels as well.

A few References:

https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-scart

https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga/ultimate

https://groups.google.com/forum/#!msg/comp.sys.cbm/ARbaCb8n9Sg/B0UPWvrKOaUJ

Nothing above is exactly what I ended up with, but that is what I based my converter off of. I used H2Obesssion’s CSync and SCART info, and then the other for the Digital to Analog and Brown fix. I would really have liked H2Obession’s “Ultimate” circuit to have worked out. There were reasons it did not work in my case, mostly I think it was the SCART Blanking. If I make another, I was thinking of trying it again.

The unit does work for me, it may not startup the Sync signal quickly enough and I have to reset the Commodore 128 to get the display to show.

The design can be adapted for IBM CGA use. The only difference there is the source of the 5Volt power as there is no Commodore AV port to supply it. Certainly a DC power jack could be added instead for a 5Volt DC power input.

The Computer Saver (C64 Saver)

Ray Carlsen created a protection circuit for the 5Volt DC line on the Commodore 64 computers, as well it can be used for other Commodore computers and other units that use a 5Volt DC input. The Commodore 64 power supplies supply both an unregulated 9Volts AC and a regulated 5Volts DC supply. The old 5Volt Regulators tend to fail and just quit regulating, causing the full power to goto the Commodore Computer, which can’t handle more than 5.5V input. When at 5.5Volts that is the maximum voltage the Commodore 64 Ram chips are designed to handle. The circuit is designed to cut power to the computer if the power goes to 5.4Volts or higher. Ray custom selects his components to get the proper fixed trip point.

Console5.com sells a kit that includes the components to build one of these circuits. Ray Carlsen also sells his as built calibrated units. The one thing is that the 5.4Volt cut off wouldn’t be ensured suing the Console5 kit. Ray mentions adding some additional resistors to fine tune it when building the circuit. I don’t know how far off it may be without doing the tuning. I took Console5’s diagram and compared it to Ray’s. Ray had since added a capacitor on the one transistor as well as a 220k resistor that were not on his schematics. With that information I decided to come up with a circuit board design using Console5’s kit that I picked up. I was able to find the Relay footprint in Eagle. I could not find the Fuse footprint though. I ended up modifying a footprint from a 20mm fuse to match up the 15mm version to. I think I got that right.

Here is the revised schematic. C1 is the added capacitor. R8 is the added 220k Resistor. I have replaced R6 with a multi-turn trimpot in the diagram, it is for fine tuning the calibration of the trip point to 5.4 Volts. This is NOT the exact diagram that was used for the prototype circuit board in the pictures.
Here is the revised circuit board layout. It has C1 and R8 as well as the Trimpot for the voltage adjustment. Below in the pictures you will see C1 is present, R8 is not, and instead of the trimpot I have paired some spots for regular resistors.

After coming up with what I hope to be a proper layout. I started to try to make the board. I had been on the lookout for a potential printer to use for Toner Transfer PCB work. I came across a HP LaserJet P2015dn. It was quite dirty, and the toner was low, but it was printing. I had been tossing around the idea of buying a new cheap laser printer, and I am glad I didn’t as I was looking at a Brother laser printer and they apparently can’t be used for toner transfer due to the higher melting temperature of their toner.

So I started off cutting down a piece of circuit board material.

Here I scored a line with a utility knife and square.

This board is a piece I picked up back over 20 years ago at school. It was old stock then.. It is very thick and very strong fiberglass based board.

After first marking it, I put it in my vice and scored the back side a little as well as the front deeper.
Here I folded it back. I was a bit impatient, and it was a very hard and high quality board. It took a good bit to snap it off.

After breaking the thin strip off I cut that down in half again. Then I sanded the surface to get any tarnish off. Any tarnish will prevent etching, or mess with it atleast. It can also make the toner not attach properly. Then I cleaned it with some IPA to get any residue off as well as any oils that may prevent the toner transfer.



Next I then split it down in half length wise as well. That was a bit easier. I then sanded the surface down to remove any oxidation. I then used a bit of 91% IPA to clean any oils.

Next I taped the cut out print to the board.

Here is wrapped the board with the print out.
Here you see the back side. No this is not the copper side.

Here we see the final result. Well I knew the toner was low and the printout very light. Due to that fact I was quite happy to get as good as I did. I wasn’t seeing any distortions, or smearing the toner. I was really testing if I could do it at all with the toner and iron. A trick to using the Iron is you aren’t trying to make the iron as hot as you can. You are trying to make it hot enough, but not so that it completely liqufies the toner. When it does that it smears it around and bleeds etc. So the other thing is that pressure has alot to do with it. I picked up a small sturdy iron ( I hope it is sturdy, it looks to be) that I could put a lot of weight on.

Well it didn’t work out. The toner was too low in the printer mostly.

Since that went pretty well overall considering the toner level. I figured I would risk a new toner for this very old HP Laserjet. I picked up a cheap aftermarket one, it worked and was better than the empty one, but the toner is not quite 100%. I also tried printing on a glossy magazine page. Both worked great, the print was great, very dark and clear. The paper took the toner well.

Here I started over with a new toner cartridge. This time using a glossy page from a magazine instead of the expensive toner transfer paper.

I prepared the other sample board, again sanding to polish it clean and IPA to clean it. I then cut out and wrapped the board wit the print out. There you can see the setting I used on the iron, a little past half way. I had read about iron temps, and used an ir thermometer to check the temp of the iron to get something close to what was recommended in a post I was reading over. I have a piece of old mdf or some fiber board there, then a smooth light blue painted aluminum plate that I placed on my workbench to iron the board with. First I let the iron heat up, then I set it on the board for a minute. I then put as much of my full weight on the iron for about 30 seconds (per the instructions I was following). I then applied heat and pressure to the board moving the iron around for another minute and a half or so. Then the board was placed in a bowl of cold water to get the magazine paper to break down to be easy to remove without pealing off the toner. I found the magazine paper to remove very easily, the expensive toner transfer paper doesn’t do that. You can see the first board and this second test here as well. The main issue I had was keeping the board from sliding around. I have some silicon thimbles (well that is what they look like), and put one on a finger to help me hold it without burning myself too much. The silicon does help alot, but doesn’t stop all of the heat so be careful. I actually use them when soldering, they also help with the heat there, but there you also can still get too much heat through if you aren’t careful.

Here is the little iron I picked up for this usage. It is small, which may be a problem with a bigger board. But I can put a lot of pressure on it with it’s design.

Here on the top you can see the new board. It came out almost perfect from what I could tell. Only about 3 minutes to transfer this design was great.

Now that new top board looks much better. There were two nicks in the print, the one on the outer marker line on the top and that little spec on the ground plane around the middle of the bottom. The spec was missing from the printout as seen above though.

My method of etching a board is based on a post I read about using Peroxide, Vinegar and a bit of Salt. I have this stuff around, it seems to likely be safer than other methods. Cleanup is easy. It is slower. I doesn’t see how it is as fast as the author said, but it does seem to work. 2 to 3 ratio of Peroxide and Vinegar, plus a fair measure of salt (enough to keep the solution green instead of blue). When it goes blue it will pretty much stop, but if the salt is added and it goes green that pulls out some of the copper from being reabsorbed into the solution basically. This is a very small board, and I have a nearly full ground plane, so the solution didn’t change color, at least that I could see in the dark here. Yes I etch it outside for safety and I don’t know what fumes come off of it if they may corrode other metal nearby. Here yo can see the reaction and that yes the copper went green from it.

Here is the board after I took it out. Just a little before I took it out, I scrubbed it with an old toothbrush and some of the toner started to come off. I could see a trace with some copper in the area that needed removed, so I put it in for a short time anyways. The copper is fairly thick on this board, and it was only a tiny bit longer. It did cause tarnish in those exposed areas.

Here is the etched board, you can see where the toner started to fail. Real HP Toner may have held up a little better.

Here is the board after cleaning with some acetone and then a light sanding again to remove the bulk of the tarnish. What is left should not hurt anything. I will inspect the board that everything is etched enough and no shorts are there. You can see that little gap at the bottom on the outline. That was that little bit that didn’t transfer. I did touch up the other mark on the top where that spec was missing with a Sharpie before etching.

Some areas do look pretty close, but it is late and I am going to get some sleep. I will be looking at this tomorrow hopefully. Then if any bridges are found I will see about clearing them up and drilling the holes for the components. I am afraid solder bridging will be an issue. Those gaps between the traces are not that big. The picture above looks to be a bout double size to the real thing when compared on my monitor. It might not be the most fun to solder. If I had made the gaps wider, it may have been hard to keep a good ground path to everything, but I could see if that could be tweaked a bit. Still I only have 1 kit here and I don’t see why I would be etching another.

If anyone wants a copy of the design let me know. The custom thing is the library that has the fuse holder on it.. I don’t know how to to share that out. I guess I could put the board files on Github or something?

Console5 Kit: https://console5.com/store/commodore-64-power-saver-circuit-kit.html

Ray Carlsen’s pages: http://personalpages.tds.net/~rcarlsen/cbm/c64/SAVER/

Toner Transfer Post: http://www.robotroom.com/Toner-Transfer-Etching-2.html

Etching Post: https://www.instructables.com/id/Is-the-best-PCB-etchant-in-every-kitchen-/

Of course after I finished the board, I found Ray had added a 220k Resistor (R8 which is on the revised layout and schematic). Well I will see about adding it in, but for my current board it would be a bodge wiring bit to get it in there for this initial test board.

I decided I had so much time in this board, and it was close enough that I could still build it and see what I came up with.

First I checked for any shorts across any of the traces, and everything checked out there. Next I moved on to using the Drill Press to put in the holes. There are several sizes of holes, all quite small. The largest size, for the Fuse Holder and Relay did fit in my drill press, although it nearly didn’t get tight. The next couple smaller sizes wouldn’t get gripped by my drill press. So I took the bottom off of my metal Pinvise Drill and put it in the chuck, I left the other size piece inside it to provide some extra support to help reduce the chances I would crush the tube. I tried to put just enough pressure on it to keep it from slipping as to help reduce the chances of damaging my pin vice. It did work out, and there was no real damage to it in the end thankfully.

Drilled board.
Here it is completed, the mounting holes are a bit too close to the circuit though. You can see there are several sizes of holes.

Next I tinned all the copper and used some solder wick to grab up any bridged areas. Then I retested for shorts and corrected one created by the solder. I next went on to test fix the Fuse Holder and Relay, they fit perfectly. I removed them and started soldering in the lowest components first. That was the Zener Diode and the other Diode. Next I worked on the Standup resistors, transistors and capacitor. Then I did the four 2pin headers, the input, output and two LEDs. I don’t want the LEDs on the board. I did not set them up as Pin Headers though, so while the holes were properly spaced being 3mm LED pads, the holes were too small. I do have some “pin type” header pins, that on the bottom side are smaller round pins and not square the whole way through. I used those. Finally once everything else was installed I went on and did the Fuse Holder and the Relay. As I went I kept checking for solder bridges, and it was a bit of an issue without the solder mask as I expected. My next board I will see about leaving a larger gap on the ground plane.

Bottom side finished. It was not the easiest to work with a board like this with such close traces it liked to get solder bridges a lot.
Here is the top side completed. You can see the two points for the adjusting resistors. I need those too as it is flipping way to early.

So I tested it out and it it throwing at 4.76Volts. That is way to early. I was concerned with the resistor values being matched at 470Ohms when Ray’s was not matching resistors. That and Ray’s mention to have those secondary ones to help adjust it. Changing the one would change the trip point up and changing the other the trip point down. In reality the two will both go both ways, if the one is set higher then it will push it one way then if it is lower it will go the other way. I guess having both makes it more flexible based on what it needed to get it right to the 5.4Volt trip point using common resistor values. So I will work on that later to get it tuned in and see what it takes.

After further testing, I found it about impossible to get the trip point set with the resistor values on hand. I resorted to using a mini potentiometer, that let me set the trip point. I put it in the circuit at R6. After doing that I found that the trip point wasn’t remaining stable. I took a long break from it as I was quite disappointed in it. I have finally went back to look at the circuit again. I had someone ask about a C64 power supply, and well I happen to need to build a second supply myself for another C64 I have since purchased and repaired. So tonight I revisited this circuit.

I did some more searching on the circuit, and found a Github project with a board design for the Saver Circuit. “OpenC64Saver”. Looking at it, it is Ray’s diagram with the 220k and the capacitor included. The only change they made seems to be swapping the one resistor for a multi turn trimpot like I had ended up wanting to do. Although my board only fit a single turn mini pot on it. I like the layout, but I don’t have Kicad loaded to be able to look at the board design except their rendering. The footprint seems to be the same footprint as the Console 5 kit includes. The resistor values are different I believe, and a few other components. It could be a good start though to get one of those boards and the Console 5 kit.

https://github.com/SukkoPera/OpenC64Saver

So I looked at my prototype again. It was still being unstable. I got to thinking, I wonder if putting a load on the output would help? By adding a small load to the output (150Ohm Resistor, should be about 36mA so not much of a load), it has apparently fixed the stability issues. I have had it running for over half an hour now and it started out set to 5.41V as the trip point, now after being warmed up, it is occasionally tripping at 5.38V but so far solid on at 5.37V. I say that is close enough to being 5.4V trip and being stable. Granted I wouldn’t use this board as built, the single turn pot can accidentally slip or get changed without warning, maybe even by dropping or such.. So I would want at least to have a multi-turn in there instead. I am also not certain that the traces on the board are heavy enough to handle the current required to power the c64 and any cartridges or other items that may be plugged into it. They possibly are, but I think if I were to use this, I would want to make up a new board with the revised layout at the top of this post, or just make the OpenC64Saver board.

Commodore 64 Breadbin #2 Referb : 326298 Part 4 Finish up.

So I had to look into the keyboard issue with the * key. When opening the keyboard quickly get the shift lock desoldered. I have heard people tend to melt and ruin the switches. I had no issues with this one twice though I was very quick with removal and re soldering it. While I was in there I pulled out the two reworked plungers.

Above is the * key pressed, it is showing about 1.6k right there, but it varied above 2k, and if pressed really hard, it went down to around 700 Ohms. When pressed very hard it did register enough to work (sometimes).

Here is an example of another key that was working. around 125 Ohms with an easy press. I desoldered the Shift lock key, quickly as mentioned above, get it heated, and pull the wires and get the heat off of it. Then the removal of the screws again as before. Looking at the board and the plungers, I found the * key plunger had all kinds of white specks of dust of some type on it. I cleaned it off as best I could. The other keys didn’t seem to have the issue. I swapped that plunger over to the “British Pound” key, as I don’t expect to use that key much. I then installed the two replacements I had one going to the * key. I reassembled and then did the test on the * key again, and this time I got 70 Ohms, so that new plunger is working pretty good. I then reconnected it to the Commodore 64 and tested it. The keys were working, the “British Pound” key wasn’t as responsive as the rest, so the conductive pad on it must not be in the best condition, so it was good I moved it.

I did the “Soft press Restore” fix as well. The Capacitor Kit I purchased from Console5.com includes a replacement Capacitor for C38. From the site ” includes a 4.7nF capacitor for C38.  Exchanging the factory 51pF for this 4.7nF capacitor returns soft-touch function to the RESTORE key. “

I had not intially put it in, I didn’t know what that modifcation did actually. So I looked it up, and it appears to be a good idea to have. Without the fix, the Restore key needs to be pressed hard and fast to get it to register. This is because the way the circuit wired to it works, it is not looking for a press, it is looking for a specific change that is a bit more digital. So it can miss a simple press, the hard press causing the switch in the button to “bounce” a number of times and one of those bounces tends to then register with the computer. It is a simple enough fix to do. That was the last bit I needed to do inside the case.

Next I put the keyboard back in the case, and installed the new plates and reinstalled the LED.

It turned out looking much better than it did originally. It is painted, so I will see how well that wears on it over time. The new badges look very good, they are thicker than the factory ones. The factory ones are about flush with the ridges around them, these are up out of the ridges a little bit. It is the special Gold remade badges. I think it looks neat, I guess it could have been about as good with the standard badges.

Below here is my stock 64. It has yellowed/browned a little bit, but it doesn’t look too bad to me. The new paint is lighter than the other unit, and I think it overall is a little light, but it is a fairly good match I think.

Well I now have the two working C64s. I guess I will need to make a second power supply sometime. I have the parts for it except the case at this time. I guess it is time to move on to another project.

I would love to hear it if anyone knows anything about the 8Pin Video mod that this had received in the past. If there is any information out there as to how it was done. Certainly removing the original port, drilling for the new one. Cutting a few traces around it to separate the additional pins. Then there are the 2 wires that were added in. I am wondering if there would be anything else involved. I think there were probably two changes in the VIC II area, but I don’t know if they are related or not. I also wonder why this board doesn’t have R36, when I have seen others that do, and a few other changes. There seem to be a lot of variations, and I wonder if some of them are recommended fixes done by the service centers to fix issues with the systems, or make them more reliable?

After finally putting it together, I noticed the power LED had quit working. The lead broke off the bottom of the LED, so I ended up replacing it with another vintage used Red LED from my parts bin. Thankfully it looks the same as the original even when lit up. A new modern Red LED would have likely been a fair bit brighter.

There is a note that the Reset Circuit relation to the 556 IC is different on this specific model of board. The schematics are not correct for it, unless there are correct ones somewhere that I have yet to find. This means that the Reset button on cartridges like the Final Cartridge iii etc don’t work. As well as on the User and Serial ports etc. I may look into modifying the board so that will work. I want to do it in such as way that I don’t have to cut traces on the board though. That is why R36 is missing, it is normally the pull up resistor on the Reset line, where in this setup it is not used and only the 556 is.

Commodore 64 Breadbin #2 Referb : 326298 Part 3 Recap & abit

I had mentioned the video fix for this board in Part 1, but I don’t believe I went over it beyond mentioning. So here it is, Ray Carlsen recommended resistor change for improved Video. These boards shipped with an incorrect resistor installed in the VIC II area, that reduces the level of the Composite Video output.

https://portcommodore.com/rcarlsen/cbm/c64/SCHEMATICS/326298/early%20board%20weak%20video.txt

The resistor is R10 next to the VIC chip. His recommended fix is to add another resistor across the factory installed one. By doing this with the right value of resistor, you can get it set to the proper value. It is easier and safer to pull the resistor and replace it. Anytime you desolder a component you risk damage to the rather delicate circuit board traces. It can be done to look very neat as well.

You should be able to see the “stacked’ blue resistor overtop of the factory installed R10. This combination reduces the value to what it should have been. That did noticeably improve the video output. The factory resistor is 300 Ohms, the resistor that should be there is 120 Ohms. So obviously the signal is reduced. When putting a 220 Ohm resistor across the 300 that takes the value of the two resistors together to to give you around 127 Ohms, so that should be plenty close to the 120 that should be there.

So I managed to replace all of the electrolytic capacitors this C64. The Modulator was quite a pain this time around. Also due to that, I let my desoldering iron sit on idle hot for too long. The tip on it started to break down, so I will have to get a replacement. It worked well enough to finish the job though.

I know some people say replace the capacitors, some people say don’t mess with them if it is working correctly.

I say I hate desoldering the RF Modulator, but as far as something causing something I may see, if the modulator caps are going bad that will affect the video output. The RF Modulator is tied in and affects the Composite output as well, as it usually passes through the modulator. It turns out on this revision though the Composite does not go through the modulator, so it seems on this revision you can possibly just remove the modulator. I haven’t verified that though, and don’t intend to try it at this point.

Above I have prepped to work on the capacitors. They are there, as well as my iron and desoldering iron, and solder collection can that I expel the solder into from the desoldering iron.

As I said the modulator was a pain. They had not “turned” the ears on the modulator to hold it in, they had bent over the small pins. I had to work the modulator loose by getting what I could off and putting pressure on the tab I had loose and hold it down while it cooled, then work my way around. I also ended up pulling the 3 square pins up out through the modulator top. That was my best bet to not lift traces. By heating them with my soldering iron from the top side inside the modulator, until it could put pulled up with my pliers that I was holding the pin with. Once they were out of the way, it was one of those pieces they bent over that was stuck in the end making it so I could remove it. I did loose some of the bottom pads, or do a good bit of damage to them where they can is soldered in with the tabs. In the end it doesn’t look too bad, the one that fell off I put back in place and reapplied solder. The one square pin lost the narrow pad from the bottom, but not the through hole thankfully. It was the audio pin and that is why I decided to just heat and remove them pulling them up out. It was a good idea. They are a tight fit, so once I had them out, I ended up using a small file to file off the old solder so they would fit again. You don’t want them loose, because they are double soldered, you risk the solder loosing contact then.

After getting the modulator off, I replaced the capacitors in it, then went and replaced the remaining ones on the mainboard before reinstalling it.

I cleaned the tabs and such on the modulator body and the holes in the board to make sure it would fit back in easily. After that I reinstalled the cleaned up pins into the modulator. In the picture the center one had some solder on it again as I had started to reinstall it but pulled it back off.

I actually pulled it off, so I could check where the traces went under it, for those three pins. I wanted to be able to make sure they were making good contact before finalizing the work. So I reinstalled it, but I did not solder any of the tabs back tight before testing.

She still worked after the replacements. I haven’t tested the Keyboard or Sound though yet. Yes I was wearing an ESD Wrist Strap and working on my grounded ESD Mat.

After it tested good, I then twisted the tabs on the modulator and soldered all of that back on. I did a bit of cleanup of the flux and reinstalled it into the bottom case. Now I need to do that keyboard work so I can put this all back together and use it again.

The new tips came. I am going to be more careful about leaving it idle when it is not in use.

Here is my desoldering tip. I have seen this happen with Copper based tips, I guess this is Brass looking? If the hot solder is left on them it starts to dissolve the metal of the tip into the solder. It is replaceable, and I like the iron so ordered in a replacement for it. Once they start doing that they keep breaking down. Other types of tips will just burn the plating off and then will quit accepting solder and not transfer the heat properly. I will not leave it idle like that while it is on again. It was while I was working with the modulator, which may have taken a hour. I was taking care to not wreck it, so it took awhile.

Beyond the modulator it was an easy recap. Most of the capacitors I pulled tested pretty reasonable but not all.

Three of the 10uF capacitors tested with almost no capacitance. Otherwise they were a little inconsistent and all of them measured above their stated values. The new ones are closer to their rated values. With those three odd ones, I feel it was worth it.

Well on to revisit the keyboard. I really don’t want to take it apart again, but the * key is kind of important. So I will get that in the next and likely last post on this refurbishment.

Commodore 64 Breadbin #2 Referb : 326298 Part 2 Case Repairs

Well I am getting back to the second Breadbin repair and cleanup as I finished up another couple projects I had put it on hold for.

I did get one of Birt’s C64 Case Saver kits to repair the damage to the case:

https://www.soigeneris.com/commodore-64-caser-saver-repair-kit

I didn’t think I could do much with the tab, and with the two cracked screw standoffs, I figured it was worth while to get it. I will have to say I am very happy with the fit and quality of the parts. I attached them with some JB Well 4400psi Epoxy.

I am doing another coat of paint on the lower portion of the case, partly in hopes of a sturdier finish, but also due to that crack that showed at one of the Din ports in the back. I had glued it, then I used some Epoxy on the inside to help it as well. I then used the White Putty in the crack to help blend it out.

With the top I cut the broken portion of the case tab off. It was the narrow one. I then installed Birt’s replacement tab. It was a perfect fit. Per his recommendation I did slightly round its edges and the two remaining tabs. I also put his parts on to reinforce the cracked screw standoffs in the top. I again used the White Putty on the outside of the crack in the right front corner of the case to help blend it out for the paint. While I had the epoxy, I decided to reinforce the inside of that crack with it as well.

The paint turned out really well. I put on about 3 coats on it. Krylon Fusion All in One Matte River Rock.

I ordered in some reproduction badges for the top of the case. Well I went with the “gold” model type labels. This thing is an odd machine, and the reproduction badges are great, but the way they are made is a bit different so it was not going to look exactly original from close up. So I am happy to make this rather neglected, and somewhat unique 64 look a bit more unique.

I have just finished replacing the electrolytic capacitors on the board. That will be posted in Part 3. The modulator was quite a pain this time around.

I still need to look at the * key and see if I can get it to be more responsive. The two “repaired” plungers are a bit off, the height is just a little wrong. I am going swap them out and keeping them as future spares. I need to open the keyboard to check out the * key anyways, I might as well switch them. I may redo them with epoxy sometime and try to adjust the height a bit more. I don’t know if that will be Part 4 and hopefully end up with it finished up.