Mortal Kombat 4 - PCB fault

Solder

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MK4 board - powers up, gives a grey flashing screen ('DIAG' LED flashes in time with the screen flashing. Sometimes the screen is simply a steady grey. PWR, I/O and Sound LEDs are on steady).

Sometimes the screen will flash Purple (just for one flash).

The surface mounted LS07 near the edge connector had burned out - replaced it but no good, not even any video sync going into this chip. Can't seem to see where the vid sync comes from - anyone got any ideas please? Am wondering if whatever fried the LS07 has fried whatever is generating the sync (etc).

No other signs of physical damage.

No sign of any lifted pins. Board in good physical condition.

EPROMs are fine (U10 was corrupted but now replaced).

Board is running rev 3.0 of the code.

Any thoughts please?
 
Well, if LS07 burned up, who knows what else fried past that point before it fried. I'm not a technician, but this exact problem has happened to a number of people because I have seen the boards on Ebay stating something similar to your problem. I even purchased one and found it to be unrepairable. Not trying to dash your hopes, but that was my case.
 
That's the curious thing, there's no fried components (mostly resistors) after the LS07. I'm guessing something that feeds it is damaged, but can't see anything obvious, which is why I'm wondering where it gets its signal from as it's proving a pain to try and trace it back to the source.

Edit: Finally traced back the video sync line - from pin 9 of the LS07 (input) it comes from a resistor near U64, from there it comes out from Moday's ZEUS custom.

Bah.

Bin it. ;)
 
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