I have a Tales from the Crypt with strange sound problems.

When I power up the machine, it sometimes lacks sound and the sound board starts up when the machine is running for a few minutes (with the Crypt keeper sample I normally hear when powering up the machine). Sometimes the start up sample repeats a couple of times.

When playing, sound is sometimes correct (with a cold machine) but after a while, sounds start missing. It's like complete samples are not played anymore. I checked the ribbon cable (reseated it) and also reseated all IC's on the sound board.

I checked power: 5 volts is present & correct, but the 12 volts is not within parameters: +12v measures 10,6v and -12v measures as -13,9v. This is also the case on the power board. Can that be the reason or is the 12v only powering the amplifier part?