Another NAD 319 problem.

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savcom

Member
Joined 2010
#1
I have a NAD 319 that is misbehaving on the left channel.
As per other threads this amp is in protect mode as soon as you switch on. The owner claims this happened since plugging in a headphone cable. I'm not so convinced. Headphone sound is fine though (especially as it's a separate circuit)
I have the service manual and have been going through the voltages and I have:

  • +/- 60V rails to both left and right amplifiers (measured on the collectors of the output transistors)
  • +/- 67V rails to both left and right amplifiers
  • Left channel measures -6V on the output (Right amp measures 0V)
  • 0V DC measured at the input of both amp boards
I think the fault lies within the driver stage of the amp but not sure where to look. Any ideas? Any more information needed? (I can upload an annotated schematic of the left channel if this would help)


Thanks in advance
 
#3
The amp is in protect mode, so there's no sound.


I'll try testing the transistors, but I'm loathe to unsolder more than I have to given the likely problems with the PCB afterwards. I'll see which ones I can do in situ first and go from there.
 
#4
Don't remove any parts before measuring the circuit's quiescent DC voltages from input to output.
Left channel seems to be at least part of the problem due to the 6V DC output offset voltage.
 
Last edited:
#5
Sorry, I didn't absorb the protection mode bit.

I definitely agree with not removing components to test. The traces can lift as soon as you touch some of them with a soldering iron. I killed a faulty PSU trying to fix it recently. I have spare amplifier boards though lol
 
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