Joe & Mac Returns schematics?

[Tailsnic Retroworks]

Hi. I'm trying to fix an original Joe & Mac Returns board using the mexican bootleg.

The issue I have is not booting, but the signal I have using logic probe on 27C4002 main code A17 entry is logic 0 with alternating PULSE led, while the correct working value is constant PULSE.

I have checked backwards and the problem comes from a 374N (I have tested it and it works). Also I have replaced the custom 156 for another working one and still fails. The bad signal comes from the VX00 GAL, but it is also working good.

For that reason, I'm searching for the schematics of this board because I don't know what is going on. Somebody can help me?

 

[ic3b4ll]

Check the work RAM. Probably messing up the bus.

 

[Tailsnic Retroworks]

Check the work RAM. Probably messing up the bus.

On sunday, I achieved to boot the game, but I have errors on the tiles. I'm investigating it.

The booting error was caused by four F245 burnt buffers and a missing OE signal common with them. The four of them surround the 156 custom.

 

[ic3b4ll]

Great work! Tilemaps are handled by the 141 custom. Depending on the type of glitches you may have to check different things.

Check the tilemap ROMs first. Probe the pins and see if all signals are there. Missing or stuck signals in the data bus will cause vertical lines in the backgrounds. If you have issues in the address lines you'll have good graphics in the wrong places.

 

[Tailsnic Retroworks]

Great work! Tilemaps are handled by the 141 custom. Depending on the type of glitches you may have to check different things.

Check the tilemap ROMs first. Probe the pins and see if all signals are there. Missing or stuck signals in the data bus will cause vertical lines in the backgrounds. If you have issues in the address lines you'll have good graphics in the wrong places.

I have replaced the 141 custom and that's not the culprit. In the mexican one, the tile rom is divided in 2 x 27c4002 eproms for not using a 27c800. I have replaced also the tile map rom and not the culprit. So, my next stop is to check the 4 buffers that receive the tiles information directly to the 141 custom.

The original glitch I had when I resurrected the board is in the first photo. The second photo corresponds to the new glitch because I found many cut traces between buffers and rams, but you can see that now all the background at least is drawn.