Need help with Nad 3020A

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Hi everyone,

I just got a Nad 3020A amplifier which does not work properly. :(

At first, it exhibited fairly large amounts of noise at both outputs. I replaced every electrolytic capacitors and cleaned every potentiometers. I am now left with these issues (without any input signal) :

- I have -9V DC at the left output of the preamplifier, 0V at the right
- I have 10V DC at the output of the power amplifier on both channels.
- Huge amounts of noise coming out of both channels of the power amp (crackles)
- I hear a component making audible noise, but I haven't been able to figure out which one (somewhere around the transformer I think)

I checked the power supply, and it seems OK. Voltages are approximately as indicated in the schematics and seem stable.

I checked almost every transistor or diode in the power amp and the preamp section and they all seem fine.

Now, I'm kind of lost... :bawling:

Anyone got any ideas ?

Thanks !
 
Only common component is the power supply really. It might be worth taking the transformer out and testing it separately. The regulated section is used by both the pre and power amp so my guess is the fault is there somewhere.

I have just retested the power supply with an oscilloscope and the voltages are OK and stable.
I am currently reflowing every solder joint, there might be an issue there...
 
Finally found it !

For the power amp, it was a fried BC549C transistor (the first one on the signal path). For the preamp, it was a BC559B and a BC549C (the first two on the signal path).

What seems odd is that they looked OK when tested with my multimeter. This might explain why I had some trouble tracking them...
 
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