Mortal Kombat 3 repair log

Received this original Mortal Kombat 3 PCB (manufactured by Midway) for repair: The Power-On Self-Test reported three bad RAM devices @U14-U36-U37 :

Board then went into game with bad graphics and colors:

The three RAM given as bad are two Fujitsu MB84256 (32K 8-bit) palette SRAM @U36-U37 and one Vitelic  V52C8128 @U14 :

As for the two palette RAMs I had no problem in finding spares and replaced them with two equivalent with same access time of 70ns:

The  one @U14 was tricky since it’s a multiport VIDEO RAM with 128K x 8 DRAM and 256K x 8 SAM (in SOJ package) rarely used on arcade hardware :

I could find three possible equivalents:

• Toshiba TC528128B
• Micron MT42C8128D
• Hitachi HM538123

I was about the order the part online when I remember I had a dead NBA Jam PCB (which runs on similar hardware) somewhere.I digged it out and found it luckily used these RAMs :

I removed the bad chip:

And installed the spare:

This fixed board completely.Job done.