Author Topic: NAD 3140 - regulated power supply - solved  (Read 311 times)

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Offline willbTopic starter

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NAD 3140 - regulated power supply - solved
« on: November 20, 2024, 06:57:09 pm »
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!
« Last Edit: November 20, 2024, 10:53:02 pm by willb »
 

Offline Messtechniker

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Re: NAD 3140 - regulated power supply
« Reply #1 on: November 20, 2024, 08:15:29 pm »
All the semi-conductors test OK out of circuit in my DCA75 tester.
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.
« Last Edit: November 20, 2024, 08:17:20 pm by Messtechniker »
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Offline willbTopic starter

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Re: NAD 3140 - regulated power supply
« Reply #2 on: November 20, 2024, 10:52:46 pm »
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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