Just picked up a Comet yesterday. Never played one before but seems to play very well. However after getting it home noticed it is missing speech and some sound effects. But other sounds are fine. I have no manual or schematics yet. I don't even know much about testing or getting codes from the pin yet, my first system 9.
After some looking and listening to the machine the effects are there but extremely quiet. I do know there are 2 volume knobs. One on the speech board and the main cabinet. The knob on the speech board doesn't seem to change any volume, will need to do some more poking.
That being said my limited knowledge of troubleshooting electronics points me to the amp circuit? Maybe the entire speech board? I can solder reasonabley well. Have a DMM but no logic probe.
Also all the ROMs are rev1 would it be worth it to get new ones?