A quick fix for a PCB that seems to develop always same issue judging from my experience and other repair logs.Received this Snow Bros for a repair:

It was playing fine but some sprites suffered from flickering (it’s hard for my camera to capture this, see from second 5 of below video)  :

Maybe you can understand better from this picture provided me by the PCB owner:

The sprites are generated by the Pandora custom chip which read data from a MASK ROM and write them to four 4464 (64K x 4bits DRAMs) :

When I went to probe these dynamic RAMs with my scope all was good except one data line (D2, pin 3) of the one @IC24, signal was weak and stuck high compared to an healty one:

Confident I removed the chip which failed when tested out-of-circuit:

Installed a socket for a fresh chip:

and tested again the board:

No more sprites flickering and game 100% fixed.

 

Got this orginal Hellfire PCB (by Toaplan) for a repair:

After some initial problem due dirty sockets of program ROMs and oxidized JAMMA edge connector which caused missing boots, I was greeted by this scenario:

Sprites were wrong, garbled and stretched all over the screen.This part of graphics is generated by the custom ASIC ‘FCU’ :

I did a reflow of it but this didn’t lead to any improvement.Probing around I found a 6116 SRAM with some data lines stuck low:

Chip failed once tested out-of-circuit:

But still no big improvements.Testing TTLs with my logic comparator I found a 74ALS169 counter @3N with bad outputs:

Its output pin 15 was almost shorted to VCC (only 7.9 Ohm measured)

Once removed, the chip failed miserably :

 

Finally the sprites were correctly drawn but blocky :

I noticed that, if I pressed down the ROM 9 @4E, sprites were 100% restored:

Removing the EPROM revealed oxidation on socket pins:

So I replaced it:

Installing a new socket fixed game completely.