NAD 906 silent

klitgt · 30th May 2012, 06:56 AM

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.

Ian Finch · 30th May 2012, 08:23 AM

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?

klitgt · 31st May 2012, 10:50 AM

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.

klitgt · 8th June 2012, 09:44 AM

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

30th May 2012, 08:23 AM	#2
Ian Finch diyAudio Member Join Date: Apr 2010 Location: Coffs Harbour, on the east coast	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? __________________ regards

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31st May 2012, 10:50 AM	#3
klitgt diyAudio Member Join Date: Sep 2004 Location: Denmark	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.