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Midway MCR Amp Buzz

posted Aug 30, 2012, 7:05 AM by super technoboy   [ updated Aug 30, 2012, 7:07 AM ]
Lots of Midway MCR series games use some version of the Dual Power Amp (Tron, Spy Hunter, DOT, etc).  The environmental Discs of Tron actually has two, since it needs to mix four channels of sound.

When I got the power supply working in my EDOT and fired it up, I was greeted with a VERY LOUD BUZZ. I really thought is was a bad ballast somewhere, and I'm not exaggerating when I say that EDOT has a LOT of ballasts to unhook. Unfortunately, that wasn't it. Nor the ground straps. Nor the CRT. Nor the big caps (already replaced).

After replacing the MB3730 amps and all the electrolytic caps on the amp boards with no improvement, it turned out to be the C3 and C4 tantalum caps.

After replacing these, everything finally sounds great!