What is wrong with my Mortal Kombat II?

[Pr3tty F1y]

Picked up a MK II PCB knowing it was broken as something to provide a challenge to learn how to troubleshoot a jamma pcb.

Was it a smart move? Probably not, but hopefully I can still make it into a good learning experience.

I do not yet have an oscilloscope, so I haven't done any testing of specific chips. I'm hoping that this is a video RAM issue and not an issue with the graphics custom.

Any thoughts of what I should target? ROMs all check out OK in the self-test as well as being dumped by a T56:

 

[mecha]

that looks like UE13 faults. that's the Williams Custom Chip, it's a DMA controller to transfer all that rom data to the rams at high speed. there's instances where it'll show UE13 bad in the power on self test and others where all the necessary chip legs are connected properly and it shows good. that's a surface mount chip. flexing the board too much can break the solder to the fine legs of the chip. if you have a small precision flathead screwdriver you can try poking all the legs to see if any move and note accordingly which ones you'll need to resolder.

if you bought the board and it was missing the plastic feet that snap into the holes around the edges of the board there's a chance since the chip legs on the underside are so long that pressing the board against a hard surface like a wooden table can fold the legs together and you'll have touching legs between chips where there shouldn't be connections. (this is a short condition!) and that could cause your graphic glitches.

sounds like a rough situation. I think I have a whole CPU board with the expansion board interconnects that works.