[sdiy] Problem with MXR 1/3 Octave EQ model 172 31 band graphic eq

[megaohm]

Hi,

  I bought a MXR 31 band rack mount EQ today at a 'fire sale'. I tested it
out and it passes audio but it has a loud buzz. The buzz is much louder than
the audio signal. The buzz is present even with no input. I can 'filter' the
buzz when I boost or cut different EQ bands.
I just started poking around and measured voltage at the regulators. 7915
shows -20 volts at the input pin and -15 volts at the out pin. 7815 shows 15
volts at input pin and 10.75 volts at out pin. All components and traces
look OK. There is a four pin chip in the power supply section , an 8302 (I
don't know what it is or does).
  If anyone could share schematics, service notes, info, or guesses as to
the problem I sure would appreciate it.

  The question doesn't seem relevant to SDIY. Any suggestions of good lists,
forums, or places to post this?


Thanks,
peng
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