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Hum in NAD 7020
Hum in NAD 7020
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Old 6th December 2010, 04:07 PM   #1
majerjack is offline majerjack  United States
diyAudio Member
Join Date: Feb 2010
Default Hum in NAD 7020

Someone gave me a 25-year-old NAD 7020 receiver that has a loud hum and no signal in one channel's output. When I bypass the output amplifier and take signal off the preamp to a separate amplifier I get both channels, so I know the problem is somewhere in the output amplification stage.

I have the service manual and schematics, and I intend to completely recap the unit. I know that hum of the kind I am hearing is a classic symptom of a bad capacitor, but how likely is it that it could be one of the output transistors that has gone bad?

Replies from anyone who has experience with this model will be greatly appreciated, and if anyone else can give me an educated guess, I would appreciate that also. Thanks to all who respond.
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Old 6th December 2010, 04:11 PM   #2
Tekko is offline Tekko
Join Date: Jan 2005
There could be electrolytic capacitors going bad.
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Old 7th December 2010, 08:04 AM   #3
gmphadte is offline gmphadte  India
diyAudio Member
Join Date: Jul 2003
Location: Dona paula, Goa
If it was kept for years without powering, then u have to change the power supply filter caps. If u r recaping, then the hum problem, most probably will go in the process.
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