Question about -12v on Williams linear power supplies

debaser138

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Question about -12v on Williams linear power supplies

I fixed up a Joust this weekend and I had a bridge at BR1 that had 1 diode shorted in it which was causing the 7amp fuse at F4 for the -12v to blow. The thing is, the game worked perfectly fine with no -12v. I looked at the schems and the -12v goes to the sound board.

Can anyone tell me exactly what the -12v is used for? I did replace the bridge but I'm curious to know exactly what the -12v is for. Thanks.
 
if I remember right, the sound just won't be as loud without -12V present. I don't know the logistics behind how or why, but that's just what I picked up along the way. my Defender came with a switcher that didn't have -12 and I was like "how does that work?" and that's the answer I was given.

since I'm psychotic, I got an original Defender PS and rebuilt it and threw that in my game instead.
 
if I remember right, the sound just won't be as loud without -12V present. I don't know the logistics behind how or why, but that's just what I picked up along the way. my Defender came with a switcher that didn't have -12 and I was like "how does that work?" and that's the answer I was given.

Hmm. Perhaps but the volume was just fine before I replaced that bad bridge.
 
-12vdc powers the sound board. The sound board has a bridge and a regulator for making it's own +5vdc.

The thing is, the sound worked perfectly fine when the fuse at F4 was blown for the -12v. Also, there is +5v and +12v coming into the sound board from the power supply as well.
 
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