AES Palette (Color) RAM Issue

[daskrabs]

I'm working on an AES that wasn't booting due to color RAM error. Diag BIOS said 5555 > 5575, so I found a broken trace from D5 on NEO-G0 to the 68K. I bodged it, and now it boots, but I still have the color problems below. Did I bodge to the wrong spot? Is there something that sits between G0 and 68K? The Palette RAM check runs fine, and the Diag BIOS reports no issues. Bad Palette RAM chip?

 

[ack]

If the diag bios says the palette ram is good, it likely is. Its possible the issue is between the palette ram and video output. I would check the 74LS273s above the palette ram. The video dac test on my updated bios maybe helpful in tracking down the issue.

neogeo-diag-bios/docs/tests/68k/video_dac.md at master · jwestfall69/neogeo-diag-bios

Disassembly of smkdan's Neo Geo Diagnostics BIOS with added features - jwestfall69/neogeo-diag-bios

github.com

https://www.mvs-scans.com/neogeo-diag-bios/19a00-master.zip

 

[ack]

I was thinking about this some more last night. Based on the your color bar picture I think it maybe an address line issue.

NEO-B1 - NeoGeo Development Wiki

wiki.neogeodev.org

I would check these

NEO-B1 PA0-PA11 <=> palette ram address lines
NEO-B1 A1-A23 <=> 68k address lines

 

[daskrabs]

Missing continuity on a A22-A23. Should I jumper direct from B1 to 68K?

Also, I don't see Video DAC test in the Diag BIOS menu.

 

[ack]

You can ignore A22-A23, looks like there is another IC in between the NEO-B1 and the 68k for them.

You will need to use this version of the bios for the video dac test.
https://www.mvs-scans.com/neogeo-diag-bios/19a00-master.zip

 

[daskrabs]

Finally got the new Diag burned and run. Here's the Video DAC results.

 

[ack]

The video dac test appears to show all fixed layer tiles being mapped to the palette entry. That palette entry is the last one that was setup for the video dac screen.

This seems to be the same behavior as seen in your color bar screen from unibios, just the flip/flop between green/red and blue/white is because of a palette ram bank switch that happens mid and end screen.

I'm not sure what would be causing this.

 

[daskrabs]

Any idea what's going on here? What are these, and could they be causing the issue?

 

[ack]

Those are ferrite beads and wouldn't be causing the issue. I'm mostly suspect there is something wrong related to your neo-b1 chip.

Try starting the palette ram loop test, while its running use a logic probe and verify all the address and data lines are pulsing.

The other thing I would personally do is in unibios goto the color bar screen, then go into the memory view and look for any weirdness between addresses 0x400000 to 0x400200ish.