NAD 3240 PE Stereo Amplifier Blows Fuses Immediately

[riffdex]

Hello y'all. I have a problem with a NAD 3240 PE Stereo Amplifier. I bought the unit at an auction, did basic testing of it (ie hooked it up to a CD player and speakers to ensure it was working) and then resold it. This is a small-time business venture I am doing with my father. We buy used stereo equipment, try to fix minor problems they may have (we are by no means experts on the inner working of stereo equipment, but we know how to diagnose simple problems). We then sell the used equipment at a slight markup to our cost (we sell via craigslist and ebay - are hoping to have our own website eventually) and we also offer 30 day warranties if anyone has problems with the products they can return it for a full cash refund or a credit. Anyways, we sold this NAD 3240 PE (it seemed to work perfectly when we got it and tested for a few weeks). About a week after selling, the buyer called to say that it had stopped working suddenly. He said it worked fine for about a week and out of nowhere stopped working. As we later found out the fuses are blowing anytime the amplifier is turned on, and we have replaced them and the same result every time it is powered on. We are trying to figure out what the problem is. We first thought he may have had a problem with his setup causing the fuses to blow but now we have it on our original setup (the same setup it was functioning perfectly on to begin with) and it does the same thing. I was wondering what would be the main causes for this to happen. What is the first thing we should check, second, etc. If anyone has an ideas or suggestions please let me know. We appreciate the help and thank you.

EDIT: By the way, I have the service manual in a PDF on my computer that contains the schematics for the unit (I am under the impression this could help) but I was unable to attach it because the PDF is 550 KB and the max attachment size here is something like 250 KB or something like that. If anyone wants I can email them it or is there any way I can upload the 550 KB service manual? If so, I can do that.

[Ian Finch]

Amplifiers that start blowing fuses do so because of shorts - like power transistor shorts and failure. If the amplifier worked fine when you sold it,
you can't rule out the likelihood that the customer simply had bad or exposed speaker wiring or connectors which shorted.
It takes only a millisecond or so to do this kind of damage. It's regrettable but I have had this issue several times myself and with clients who
expect even old equipment to be fully idiot proof. Some amps seem fine until you test the protection and realise (too late) it's disabled or not working.

Are both channels fused separately and only one channel failing?
Initially, test the output transistors for B-E diode voltage on your DVM and measure also for shorts across C-E. Compare the readings of each channel.
A link to the site should work. Nad Diagrams, Schematics and Service Manuals for FREE

[tauro0221]

Hi,
You have 6 fuses and 3 bridges. Which of the fuses are blowing?????