mega drive rgb bypass csync, 2k2 resistor and cxa pin 10 questions

[Seroczynski]

Hey, I’ve been working on my SEGA Mega Drive (Genesis for you lot) and I’m having a few difficulties when I follow your guide. I’m trying to install this on a PAL VA4 Mega Drive.

1) I’ve prepared the R, G, B and CSYNC pads. The next step involves cutting four traces from the bottom of the board. I’ve succesfully cut the traces for R, G and B. However, my CSYNC is located on a different location, which confuses me as to which trace I should cut. Here’s an image of the bottom of my board, I’ve highlighted my RGB signal, my CSYNC and the reference location (C103, which I got from the guide):

2) I have the newer version of the RGB Bypass board, the one with the Sonic logo on it. Do I still need to install a ¼ Watt or smaller 2k2 resistor, or is this handled by the RGB Bypass board?

3) Do I still have to cut the trace on pin 10 of the CXA chip?

Thanks in advance!

[TheCorfiot]

Firstly you can ignore the 2k2 resistor as the guide clear states it’s already fitted on your board…

If you follow that circled via to the top side of the board you will find the track leading straight to the VDP chip.
You need to cut this track right by the via on the top side then clear away some of the green solder resist on the remaining track going to the chip leg, it’s quite a big area, then solder the CSYNC wire there…

And yes you must still cut the track on Pin 10 of the CXA Encoder

[Seroczynski]

Thanks, I’ve completed the steps but now I get “NO SYNC” on my OSSC. I’ve double-checked all my work, including trace cuts. Here are two pictures of my work:

I’m not sure what I might have missed. I’m using a 2017 RetroGamingCables RGB cable (pre-packapunch) for the Model 1 but am unsure about the specification of this cable. I would assume these cables should be fine.

[BuckoA51]

I’m using a 2017 RetroGamingCables RGB cable (pre-packapunch)

You need to make sure to use a cable using clean sync, composite video for sync cables will not work.

[Seroczynski]

I’ve had to use Wayback Machine to double-check what my exact cable looked like, and I guess it indeed might not be compatible with upscalers/line doublers. Going to order a Packapunch cable before I’ll report back.

[Seroczynski]

Alright, I got the Packapunch cable and tested it on my OSSC. Still NO SYNC. When I plug the Packapunch directly into my TV’s SCART I get a continually, vertically scrolling screen (from bottom to top). So I guess it must have something to do with the CSYNC signal. I’ve yet to figure out how to fix it. Does someone know why I’m getting this result?

[Seroczynski]

I’ve continued this thread on the OG forums, but wanted to share my current situation here in case people are having the same problems. Here’s a video of my current signal when connected through a proper Packapunch RGB cable directly to my TV (as the OSSC get’s NO SYNC):

[James-F]

BOT warning!
Don’t click it!

[BlueStinger]

To connect the RGB, Sync an 5V from the chip and 7805 I used a shielded wire, with the shielding grounded on both ends. Also route them as far away from IC9 and 10

(This install unfortunately is quite overloaded)

Now as a final thing I plan to do a recap. pic.twitter.com/ufJLYlxGcO

— Consoles4You (@Consoles4You) July 28, 2019

First, Consoles4you have seemingly found an answer to the remaining jailbars on PAL consoles, apparently the answer is : Do as usual but use shielded wires to do the install.

For this particular issue, I had it (and many others) then I’ve RGB Bypassed consoles and removed CXA entirely. Don’t do that ! It will work for a while and then it won’t work anymore. While CXA was missing (and before it was an issue) everything was fine. Lately, I’ve been re-installing CXA in those consoles and now I have those same old issues reappearing.

You can remove CXA on NTSC consoles but NOT in PAL consoles. Also, and I need a little more time to confirm that, CXA can apparently be responsible for a ton of other issues like random reset, garbled graphics, sync issues.

I can elaborate to prove some of these points if needed. But my advice right now is : Try to swap CXA for a good CXA chip.

[Seroczynski]

Thanks for pointing that Tweet out, very interesting.

I am thinking about just purchasing a NTSC-J Mega Drive and use the RGB bypass chip on that system, seeing as it’s mainly the PAL consoles that are being affected by these issues.

[Author]

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