Still another “portughese” PCB, a Sunset Riders :

The board was unstable, most of times it didn’t boot and kept resetting (watchdog active), some times after some reboots it got past the self-test and entered in game but sprites were missing.If I pressed/flexed the board, they appeared.Here’s a video for a better understanding:

I noticed someone previously tried to fix this issue by reflowing the two sprites generator ‘053244’ and ‘053245’  (forgetting to remove flux residuals )

The reflow was done properly but it was not enough, anyway there was for sure a bad contact in this area. At a closer inspection I found that a pin of the near ‘054358’ custom had its pad detached from PCB, this caused intermittent contact with its trace.Here’s a close-up under a microscope:

I promptly restored the connection, in this way the board booted all the time with sprites too.But playing the game I noticed some little glitches :

The glitches got worse if I put my fingers on the solder side of the two palette SRAMs (2K x 8-bit devices)

The one @14D was already replaced and socketed, probing the other one @13D with a scope revealed unhealthy signals on some data pins  :

This lead me to remove the device and test it ouf-of-citcuit where it failed:

Replacing the RAM fixed board completely, another successful repair in the archive.

Received from Portugal a batch of faulty PCBs for repair, there was among them this Bomber Man World (on Irem M97 hardware)

The PCB was working fine except for the sound, you could only hear some scratchy noise and also video output was affected showing some kind of disturbs:

This is scenario I faced many times during repairs and the cause was always the same : the electrolytic capacitors.In particular Irem boards suffers from the “brown ELNA” syndrome and this was not an expection.I  went to measure capacitors with my ESR meter starting from the 470uF 25V one @C203 which filters the +12V routed to to sound amplfier.My meter didn’t display any reading meaning the measured ESR value was out of range (from 0 to 99 Ohm on my meter) 

Probing the +12V line with a scope confirmed there was some ripple (no longer filtered by this capacitor)

The out-of-circuit testing  confirmed the high ESR and bad capacitance :

Fitting a good capacitor restored loud and crisp sound.End of job.