Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

 
 
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Default VR-407 unbalanced supplies

I have a Kenwood VR-407 which keeps going into protection. The ±12VDC
supplies are unbalanced. The schematic for the circuit is posted in
a.b.s. It's just a basic circuit, it uses a center tapped transformer
feeding into a full-wave bridge, with the center tap grounded, with a
positive and negative three terminal 12 volt regulator. No rocket
science here. However, the supplies are unbalanced, pretty severely.
The input to the bridge is 14.24 & 14.15 VAC. The output of the
bridge is -25.28 & 10.23VDC with .685 & .240VAC ripple, respectively.
I pulled the board from the unit and powered up each regulator
individually . With -18VDC in across the negative, there was .1A draw
& -11.90VDC out. With +18V in across the positive regulator, there
was .1A draw & 11.83VDC out, so the reguators are fine and neither has
excessive current draw down the line. When I put an external supply
across both bridge capacitors I saw the same unbalance. With 35VDC
across the caps, there was 25.94 across the negative cap and 8.99V
across the postitive cap. I connected a capacitor in parallel across
both caps individually, but it didn't create any significant change.
Is it probable that one of the caps is bad causing the unbalance?

Thanks, and I'll provide any more information if necessary.

 
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