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.
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