My NAD C272 has developed an intermittent fault where the left channel goes completely dead until I give it a good wallop, at which point it returns. It seems to get more reliable when the amplifier has warmed up. So I assumed it was a dry joint or intermittent connection, but when I took the back off I was unable to replicate the fault. Its not the pre-amp or source components, because the problem stays on the left speaker when I swap the amplifier inputs over. I've replaced the cables with no effect. Has anyone seen similar problems? Do you know where I can get hold of a technical manual?
My solution was actually indeed the output protection relay. What I did was to open up the relay and use contact cleaner and a very fine abrasive to clean the contact surfaces of the relay. After that, the problem was gone!
The way to diagnose this for me was to run the amplifier open until the problem recurred and to simply tap the relay's box. The sound came on immediately, and I was convinced.
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Re: NAD C272 Amplifier: Intermittent left channel
Based upon your description of the problem, there are a few possiblities. First a question: does this problem occur more often with low volume? If so, I'd suspect a bad output protection relay. If it is independent of the volume, resolder all of the connections in the output section. It may not look like a bad connection, but it is there.
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Check the speaker wiring for shorts, a common problem. If everything checks out there may be bad solder joints on the main board especially in the output stage, or there is a fault in one or more driver transistors.
Normaly this is what cause little volum and distortion. Check first if you got +68/-68V on amp module left and right Often the -68V is missing. This is caused by faulty transistor Q712 (2SA872) in +68/-68V power supply.
You need to look inside. There will be a fuse inside too. If your lucky it will restore the amp once replaced, but if it blows again you have a fault. You can track it down yourself if your any good, you might even see a burnt out part when looking for that fuse, otherwise get the repairman in.
Hi Jimbob. Sounds like you have dirty/dry controls/switches. The contact lubricant dries out on them producing intermittent and scratchiness when you operate them. Clean any offending controls or signal switches with CRC2-26 by squirting(to flood then internals) each control/switch. you will have to do this from the inside of the amp. You may also have a dirty speaker protection relay, sound may return to a dead channel when you turn the vol up points to that. Good Luck. If you need more info feel free to get back to me here. Happy to talk you through more if you cant sort it out.
It is most probably a dirty speaker protection relay. gently tap the relay(the one that engages shortly after turning the amp on) when the fault is occurring and see audio returns. This should ascertain the problem. Replace it if it is a sealed type, or if it has a "lid" you can get off, burnish the contacts with a white business card, and give it a spray with contact cleaner/lubricant. Good luck and a "fixYa" rating would be great for my profile :)