Galaga buzz

ManiN

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I recently acquired a Galaga that had a bad power supply. I put a switcher on it and all is well except there is a light buzzing sound that comes out of the speaker. It's not horribly loud, but loud enough to be annoying. The noise sounds like interference like you hear in cheap stereo amps etc. 60Hz buzz etc. Bad filter? New ground for me.

Any help is greatly appreciated.
 
Unplug the marquee fluorescent and see if it goes away... The speaker wires run next to the AC for the light, and if the ballast is going, 60/120hz noise will couple in...
 
I'll check the light.

I swear I've seen elsewhere where someone said "installing a switcher will produce a buzzing sound"
 
Forgot about the marquee light. Its quick and easy to check and will surely cause a hum if the ballast is having issues.
Sometimes running 120v wires in the same bunch as the other wires can cause issues too.
I have a switcher in my Galaga and its fine.
 
Just an update, I decided I'd rebuild the original power supply to see if that would help. It now works, but there's still an interference buzz. It's not the same, just a little different. I think I may pull the boards and look for bad traces to see if there may be a ground issue. Seems the filtering is not performing like it should.
 
I think I checked it, but maybe couldn't tell cause of the switcher... I'll try it again with the rebuilt PS and see. That'd be sweet if it's that simple.
 
So, I recapped the board, checked the marquee light, and this bitch still buzzes... Makes me think something's up on the board. With that, I have no idea where to start...
 
Is there anything involved in the power supply in the bottom of the cab that might cause this? I've tried disconnecting the marquee light, put in a switcher, rebuilt the linear power supply, recapped the board set, grounds all seem fine, frame ground on plug is present. Just not sure what failed that would eliminate the buzzing noise???
 
It could have something to do with the a/c cord. In car audio, a noise in the system is often due to a bad or insufficient ground. I would try swapping out the a/c cord with a new one. It is cheap and worth a try.
 
Ended up doing a band aid fix of putting a 470uF cap across the speaker leads. Lowered the buzz to a level un noticeable. Gonna go with it.
 
If you can hook up a 12v battery to the +12 to see if that will eliminate the buzz. This will usually stop the buzz and if it does then you know the buzz is coming from the power supply.
 
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