PCB Repair: Ultimate Mortal Kombat III

Problem

Dead.

Diagnosis

The PCB looked as if it had been left outdoors. The solder-mask was bleached and the socketed ICs had rather corroded legs. Some ROMs had been removed, breaking off legs in the process. Wedge under many of the ICs and sockets were what appeared to be seeds/grains. At least that’s what I hoped they were…

Seedy.jpg
Not entirely sure what they are but they don’t belong here…

By swapping in a pair of new program ROMs (U54 and U63), I was able to get the game to boot:

MK3_ROMS.jpg
Uh oh

U102-U133 are the graphics data ROMs. U110-U113 and U118-U121 are mask ROMs, which actually tested good. U130 tested good because it was a known-good EPROM taken from another PCB. Sound EPROMs U2 and U5 were intact but the sound section test failed regardless.

Had all the graphics ROMs tested as bad, the CPLD at U35 would immediately be suspect, as this controls the ROM /CS lines. I removed all of the EPROMs; many of which were in a rather sorry state. I tried verifying some in my ROM programmer. Those that I could successfully read (most hit a ‘Continuity Test Fail’ error, even thorough pin cleaning) were full of garbage.

I swapped all of the EPROMs with those from a faulty PCB with good ROMs, cleaning the sockets as I went. This was sufficient to get the game running.

I left the PCB running overnight to see how it fared. When I returned the next morning, the sound had stopped working (U1, the ADSP-2105, was shown as bad). Bugger.

I probed around the sound boot ROM (U2) and found that the A10 line was stuck high. I traced this back to a 74HC541 at U58, where I found a bad output:

mk3.png
Yellow: Input (pin 4), Green: Output (pin 16)

I replaced U58 and left the game running overnight. Thankfully this time it survived the night!

Fix

Replaced all EPROMs.

Replaced 74HC541 at U58.

 

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