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Old 30th May 2012, 07:56 AM   #1
klitgt is offline klitgt  Denmark
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Default NAD 906 silent

My good old NAD 906 has become silent in one of the 6 channels. I must admit that I short circuited the speaker terminals on the now silent channel by accident and now my question is how many components I can expect are damaged? Maybe only the power transistors Q421-Q423 (MJ15022-MJ15023)?
Any ideas as to a solution? Schematic shows the left channel in one of the 3 pairs of channels.
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Old 30th May 2012, 09:23 AM   #2
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Can you tell us whether the on-board fuses have blown or what voltages are present on the output terminals as it is?
Are there signs of damage to parts around the output stage?
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Old 31st May 2012, 11:50 AM   #3
klitgt is offline klitgt  Denmark
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Thank you Ian, I mentioned my problem to my son-in-law who said he would be interested in trying to solve it. He is a technician with access to repair facilities. He took the amp with him yesterday evening and I will pass on your message.
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Old 8th June 2012, 10:44 AM   #4
klitgt is offline klitgt  Denmark
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A good piece of advice: Look for even microscopic disconnections in the copper traces, also far away from the output stages. In this case I found the problem at the input pcb between the bridging switch and the line output connector (marked red on schematic).
Now it works fine again
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Old 31st December 2013, 06:01 PM   #5
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Quote:
Originally Posted by klitgt View Post
My good old NAD 906 has become silent in one of the 6 channels. I must admit that I short circuited the speaker terminals on the now silent channel by accident and now my question is how many components I can expect are damaged? Maybe only the power transistors Q421-Q423 (MJ15022-MJ15023)?
Any ideas as to a solution? Schematic shows the left channel in one of the 3 pairs of channels.

I'm sure you've fixed it since you posted last year, but if not: just check the fuses. I have a NAD 906 and I love it to death. I once shorted the speaker terminals on one of the channels and heard a pop, same as you. Turns out that it was just a fuse. For that model, you must remove the chassis cover, and after 15 seconds of investigation you'll see that each of the three amps inside has a glass fuse. Just see if one is blown, and if so put a new one in. I practically guarantee you that's the problem.

BTW, I think this is one of the best designs NAD ever made. Bridged, you get 90wpc, and given NAD's conservatism that is absolutely a **** ton of power, particularly since the mains are only running high-pass above 80hz. Super flexible and the absolute bare minimum of aesthetics that you could ever have (can't stand flashy looking gear). A power amp isn't really subject to NAD's oft-cited reliability issues because there are no moving parts. I put an IEC inlet on mine so it was easier to plug in, and used that opportunity to clean things up inside.
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