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Old 25th September 2009, 05:55 PM   #1
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Join Date: Feb 2009
Default Need help with NAD C350

I have searched a bit for a similar problem, but didn't find anything.

Here is my problem:

When I power on my amplifier, a relay is clicking and the Soft Clipping LED is flashing then the relay releases again, then it starts over. It clicks and flashes about ones every second.
I noticed it first when I turned on the amp after it had been off for a while. Then I let it go clicking away for some minutes. After a while it clicked and flashed less frequently, then it stopped and it switched on and worked as before. I guess it slightly changed a value on some component as it got warm.

I suspect I have some old capacitor somewhere that needs to be replaced.

Before I had the problem with the power LED going red, but with help from some forum thread I managed to find the faulty capacitor then.

I can add that I have not done anything special, also, nothing changes if I turn off soft clipping.

I would be happy for any help I can get!

Best Regards,
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Old 25th September 2009, 08:20 PM   #2
anatech is offline anatech  Canada
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Join Date: Jun 2004
Location: Georgetown, On
Hi Vincent,
Well, you already know that the protection circuit is working. You can not assume anything until you have more answers though. It would be unusual for a capacitor to cause this problem, not impossible.

I don't have a schematic for this model. Do you know if it's the same as another, or can you send me the manual or schematic for this?

Now, I'd suggest your first step in troubleshooting would be to look at the output from each channel with an oscilloscope as the amp turns on. You will probably see a DC offset (a complete guess on my part) on one channel, causing the protection circuit to operate. You may also have a power supply fault affecting the actual protection circuit. Look at the supply voltages that run that circuit. Again, use your oscilloscope. Your initial vertical sensitivity should be 10 V /cm or higher to start with. Trigger in the line frequency as I'm thinking you may have a supply fault and it doesn't matter what you trigger on for a DC fault. You just need to have a sweep to observe.

Let us know what you find.

"Just because you can, doesn't mean you should" my Wife
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