Loud Midrange Squeal

Discussion in 'General Electronics Chat' started by neilbeste, Jul 8, 2013.

  1. neilbeste

    Thread Starter New Member

    Jul 8, 2013
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    I have become the owner of a Soundtech PC-1250 Powered Mixing Board, and I am interested in making something more than a boat anchor of it. When I obtained the unit I was told the building it was in had suffered a lightning strike, and it hadn't worked since. I took it home to find out what I could and I am stumped as to how to proceed. When it powers up, it emits a constant midrange squeal that is very loud out of all four outputs: R, L, Mon. A, Mon. B.

    If it were silent I know a thing or two to try. I don't own a scope. Can someone please help me to isolate the origin of this signal so I can proceed?
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Do you have a schematic of the board?

    The failure is something common to all channels, such as the power supply.
     
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  3. neilbeste

    Thread Starter New Member

    Jul 8, 2013
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    I am working on obtaining the schematic. Soundtech evidently has a strange relationship with the public and professional community. Does anyone on this forum have the schematic?
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    When I was being trained centuries ago..... the cardinal rule is:
    Always assume the power supply is the problem until proven otherwise.

    A lightning strike could over stress and damage just about any component. What happens is the parts that "break down" first act as zener clamps to save the other parts. Post a schematic and we can all guess as to who died first.
     
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  5. neilbeste

    Thread Starter New Member

    Jul 8, 2013
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  6. neilbeste

    Thread Starter New Member

    Jul 8, 2013
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    Found the schematic. some of it is difficult to read. Checking what I know how to check.
     
  7. neilbeste

    Thread Starter New Member

    Jul 8, 2013
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    Showed this unit to a friend. He agrees it's probably a pwr supply issue, but gave me reason to skeptical of a lightning strike being the cause.
     
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