Q*Bert Humming

modessitt

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So - I brought a Q*Bert into the shop today with no sound. Rebuilt the burnt +30vdc circuit in the power supply, and now all my sounds are there, but I have a constant hum that doesn't change with the volume control. Got to this point at the end of the day, so I haven't done anything else yet.

Obviously, I will make sure it's not caused by the marquee light, but other than that, would I be looking at a bad 2200uF cap on the power board not filtering properly? Leaky caps on the sound board? A ground issue? Bad amplifier?

Still have to replace a burnt-up knocker, so any other help would be great. I know "Q*Bert" and "sound problems" are heard often, so figured I'd ask those who've messed with it a lot....
 
I know how you feel, I post some questions and sometimes never hear an answer at all.

It's probably going to be the LM379 sound amp, which is uses that 30V you rebuilt. Is it a 60Hz hum? You do know there are actually two volume adjustments right? one on the sound board as well as the one in the coin door.


Luke
 
Maybe it hums because it doesn't know the words?

I dunno. Check your grounds, filter caps, etc. I take it that is's a 60hz type hum?

-Ian
 
Reflow the filter board for fun, because that thing is a POS. I had a distortion that caused issues with the video, it was pointed out to me that it might be a bad common ground from the monitor. Not really your issue, but I guess just be thankful Qbert does anything at all!
 
Well, I fixed it before I got back and saw your suggestions. Burnt pin on the filter board, and a trace on the filter board was burned through....
 
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