PCE help diagnose video problem

[Chrom_]

Hi all. This is my first message in the board, and I'm very glad to be part of this community. I hope I'll be able to give help, more than I'll need.
   
On my JPN White PCE (RGB modded) I'm getting corrupted sprites and backgrounds. The characters look fine instead. I'm planning to check the continuity of the traces this weekend because I have a vague suspect for a cut trace between the 6270 and the flat cable. There a bit of solder mask and possibly traces that came off under L102. Could it also be bad RAM?

Any idea or your past experience in similar problems is a very welcome help. All relevant images posted here






Here's an high res pic of the board. The place where I suspect a cut trace is in the lower left part of the image, between L102 and the area where there was the RF unit (removed for RGB mod)


Thanks in adavance for any sugestion

[Keith Courage]

It's either bad ram or bad traces between the ram chips or Hu6270 chip.

The memory/ram chips are the top two in your pic that are identical.

[Chrom_]

I'll check all the traces as soon as possible. In the case the traces are OK, is there any trusted selled where RAM chips can be sourced?

[Chrom_]

Today I've checked for continuity ALL the traces going from and to the 3 main chips and the 2 RAM banks, no broken traces found. I've also checked the continuity to and from the HuCard slot, with no issues found. After that I've checked the voltage regulator, and it outputs exactly 5 volts. After that I have checked ALL the chips and RAM pins with a logic probe, and I see pulse to all the RAMbus and DATAbus. I'm really out of clues now. I have tried to bypass the RGB amp, but I'm not sure I managed to bypass it completely, so I can't say if the test was relevant. could it just be a broken HuCard? I don't have another one at the moment for testing. Any other idea to help me?

[pnauts]

I have a weird PC genjin 2 which make some glitches with incorrects backgrounds like you.
As you don't have another Huc, I think that it could really be the source of your issue.
Get some Huc to confirm.

[esteban]

Yes, I have a PC Genjin 2 with glitches as well.

[Chrom_]

I'm sourcing a few hu cards, so that I'm able to test. If it's not that, my last hope is to bypass the RGB amp completely and see what happens. If that fails too, I may try replacing the RAM, but I have no idea where to get some spares from

[mickcris]

you can try to hook up composite video to the expansion port.  not sure if your tv supports NTSC composite video, but this would be bypassing the RGB amp.

http://www.cgquarterly.com/articles/tg16_cable.htm

[Chrom_]

Today I've completely bypassed the RGB amp by tapping svideo from the EXT slot. Same output.

At this point the chances are:
- broken Hu card
- some strange fault at the RAM level that is not evident with the logic probe

I still have one doubt about the small IC that is located on the Hu Card reader doughter board. Pin 1 seems connected to +5v or GND (I get continuity), but it is the only pin that gives me no reading with the logic probe. Any idea about this?

Also any reference for RAM spare parts?

Thank you all

[pnauts]

Do you try to reflow this pin ?

[Chrom_]

I'll get a couple of new Hu Cards next week. I'll test the unit with the new cards first, then I'll try reflowing. I'll keep you posted guys. Thank you all

[Chrom_]

I have tried with 2 other Hu Cards, and unfortunately I have the same videou output problems. I have noticed that to make the hucard work I had to plug and unplug it a few times. I have also noticed that the 6270 runs considerably hotter than all the other chips. Is that normal?

[thesteve]

if you have a chip running hot odds are its a bad chip (unless its got pins bridged)

[Chrom_]

Is there any good method of finding if there's a bridged pin? Would checking continuity between pins work even if most of them refer to the same databus or IObus?

[Chrom_]

Visually I'm not able to see any bridge... Check the attached image