Feb 282011
 

Bought this a little while back as spares or repair. The fault was it had no sound but due to my scope packing in I never got around to fixing it until now.
The board is in outstanding condition and very clean.
I pulled out the schematics for this board that I had stashed away and began working my way backwards from the amp.
I found the analog output from the YM3012 was dead, replacing this chip brought back the music but some of the sound effects were still missing, namely the attack sounds. I recreated the fault using MAME by corrupting the ADPCM ROM 21j-6. From here I could trace the fault from the ROM right through to the amp.
I traced the fault to IC80, M5205 (ADPCM Speech Synthesis LSI). I could see the data going into it but pin 10 (output) was silent. Replacing this brought back the effects and completed the repair.