Vintage Synth Repair

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> 1. power supply help
> From: "sabolick" <sabolick@...>
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> Message: 1
> Date: Sat, 10 May 2003 22:52:12 -0000
> From: "sabolick" <sabolick@...>
> Subject: power supply help
> 
> Hello to all:
> 
> I am repairing an oberheim OB-X.  Unfortunately, I'm stuck and
> need a little help to get over the hump, hopefully someone will be
> able to help.  I usually do amplifier repair, and this is my first
> keyboard.
> 
> Problem.  The first (physically closest to the x-former) bridge
> rectifier is heating up, and the board underneath it is charring,
> causing smoke.  I replaced the original rectifier and re-capped the
> supply, carefully noting all the polarities.  The x-former
> secondaries check out, and are symetrical.  After replacing all the
> filter caps, I brought it up with a variac, and the same thing
> occurred: abnormal heat from the rectifier, and charring/smoke from
> the pcb.  There was no load was connected to the power supply
> section.  I checked the test points while it was on, and the
> specified 19 volts was absent.
> 
> Now this thing did sit for a while, hence my off-the-bat re-
> cap.  My experience says that the pcb has become conductive between
> the bridge's connections, but I've never worked on anything that
> used this type of pcb before.  Is there something I am missing, or
> anyone with experience in this sort of problem?
> 
> 
> Thanks very much
> 
> 
> Mike
> 
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