Electronics > Repair
NAD 3140 - regulated power supply - solved
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willb:
Good day all!

I have been chasing my tail for 2 days over this issue and can't seem to get anywhere.  |O

Basically, the positive rails in the power supply are good but the regulated negative side is no good. All the semi-conductors test OK out of circuit in my DCA75 tester. I replaced the few electro caps, no difference. All the resistors are good. I have attached a photo of the schematic with the voltages I have in red at the measured point. I am at a loss.

Any insight would be greatly appreciated!

Cheers!
Messtechniker:

--- Quote from: willb on November 20, 2024, 06:57:09 pm ---All the semi-conductors test OK out of circuit in my DCA75 tester.

--- End quote ---
According to your measurements that BD 140 with both collector and emitter voltages at at 55 V shoud be dead.
If on a heat sink, bad isolation could be shorting out this BD 140.
willb:
it's fixed.

Someone was in here before me, replaced Q808 but installed it backwards, swapping the emitter and the base.  :palm: :palm: :palm:
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