Image Fight repair log

Received from Japan an Image Fight PCB for repair (game is a vertical shooter  developed and published by Irem on M72 hardware)

On power up the board seemed to properly boot, something moved on screen but then got stuck on garbage :

As many of  you may know, this is a three stack set hence, having a good R-Type boardset, I started to swap boards.I was able to narrow the fault in the bottom PCB :

 

First of all I probed these four 8k x 8-bit static RAMs @IC34-IC35-IC36-IC37 :

I found that their WRITE ENABLE input (pin 27) was stuck high, no activity/pulsing like observed on my good R-Type :

Tracing the signals back I could not find anything abnormal until I came across a 74LS32 @IC51 :

 The logic analyzer showed no LOW pulsing on output pin 11 when inputs 12 and 13 got asserted :

I piggybacked the device and board booted into game although background graphics were corrupted :

 

I removed the TTL device and it failed the out-of-circuit testing :

Time to install some machined round socket and a good IC :

The next power up gave me a fully working game with no other issue.Repair accomplished.