Need a bit of troubleshooting help. Thanks in advance.
I am refurbing a Blackout. Had been stored safely for years nonworking. Repaired a couple of bad solenoid drivers/swapped the coils. Did the following general refurb:
1) Replaced female side of interboard connector. Replaced all solder on the male side.
2) Replaced solder on all headers on all boards.
3) Cap replacements on power/sound boards.
Everything looked reasonably stable until about a week ago. Then it started resetting/flickering displays/bright lamps. Then the sound died entirely.
I pulled the sound board to learn how to boot it on the bench and noticed that the game is stable without the sound card in it. Okay, so we have a sound board problem. I took a second sound board from a BK that had been stored/working and put it into the Blackout. BK sound board acted exactly the same way - not even speaker hum. And the game started doing the same resets again.
Last night I finally thought to check impedance on the speaker and couldn't get a reading. Swapped in an 8ohm speaker I had around quickly and got some sounds from the BK board. So somehow the speaker had crapped out in this situation but I can't think of how that may have happened. Maybe it's just a coincedence.
So assuming that both sound boards don't have exactly the same problem I'm trying to figure out how the presence of a sound board would cause the game to be unstable. Looking at the power diagram I see that the sound board does not pull power through either of the BRs nor through the power board. It gets AC directly off the transformer but it does come off the same 18.7vac winding as the logic supply. Could the sound board be somehow pulling too much and causing logic voltage to drop even though they're both coming right off the transformer?
Any suggestions are extremely welcome!