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:

Part 2, Board Design and Part List:

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:


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