Rush & Crash repair log

Received from Austria some faulty PCBs for repair.I started my job from an original Rush & Crash (the japanese release of The Speed Rumbler), a shooting game released  by Capcom in 1986.

PCB is a two stack one with a top board (where main and sound CPU circuits lie) :

And a bottom one :

The fault concerned the graphics as backrounds were totally missing/wrong or disappearing :

All the graphics is generated on video bottom board so I focused on this one.Many Fujitsu TTLs drawn my attention hence I went through them with my HP10529A logic comparator.Quickly I found a 74LS74 @7D with two suspicious bad outputs :

 

I removed the IC .

Chip failed the out-of-circuit testing :

Fitted a good IC :

This restored the backgrounds but playing some games I noticed the sprites were slightly glitched by some tiny lines through them :

 

The sprites circuit lies on bottom board, data are stored in eight 27256 OTP ROMs and then sent to two custom ICs marked '86S100' (which is basically a shifter) 

I made a reproduction of this custom chip time ago (actually I made two versions because the original part can work in two different modes)

Capcom '86S100' reproduction

Hence I know how it works and where to check for its proper functionality.Probing the two '86S100' revealed a lack of data on an output of the one @13E, you can see how the signal of the below left picture has less transitions than the one on the right:

I removed the IC and installed a repro of mine :

This fixed the sprite issue :

Board 100% working and another repair accomplished.