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NAD T762 fault

Hi I have recently tried to repair a T762, not very succesfull I'm afraid. The story is this: I was listening to music one day and suddenly the amp shuts down with at loud POP in the speakers and red light in the status led. I turn it off and then on again and now there is nothing coming out of the speakers, other than hum when I turn the volume up to max. After some checking I find that it can still switch between video feeds and the main amps still work if I use direct input. After some seaching in the schematics I'm guessing that it has to do with a missing voltage, and sure enough the +12V is missing. After half an hour of disassembling I have the motherboard out, and I measure the 5V1 zeners and one is dead. I exchange all 5V1 zeners with 5W types an reassemble the amp, but now it will not turn on. The status light is amber, but no turn on. I measure the power on +13V and find it about 6,5V at D712. it seems that some thing on the +5,6V is drawing to much current for the poweron trafo.

Does anybody have any sugestions?

Torben

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Reply to
Torben Espoe
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check some electrolytic caps for shorts.

--
"I'd rather have a bottle in front of me than a frontal lobotomy"

http://webpages.charter.net/jamie_5"
Reply to
Jamie

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A Google search seems to indicate the NAD T762 might possibly be one of those "lemons" of domestic electronics we sometimes come across.

While this doesn't help much, a similar problem was covered on sci.electronics.repair earlier this year, but without any positive outcome.

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Reply to
Ross Herbert

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Thanks for the fast replys

I have read about the "hot zeners", and it seems that my T762 have the same problem. But im a bit clueless as to why the amp fails to start up now that I have replaced the faulty components.

Torben

Reply to
Torben Espoe

Torben,

I'd start by checking that all of the plug in cables are seated. The one that (as I recall) runs from the keyboard (front panel) down to the mother board (4 pin black wire) is easy to forget. Be aware that I may be thinking of the T753, which I see more of. Also, be sure that the trigger switch on the rear (if so equipped) is in the correct position. It's easy to move by accident when putting the amp back together.

Regards, Tim Schwartz

Reply to
Tim Schwartz

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I am not able to provide any help since I don't have the schematic, and even then this probably wouldn't help to isolate the cause. The only thing which I can suggest is that there is possibly some other faulty component (such as a shorted rectifier in the power supply bridge rectifier) or other device. Since the number of reported complaints of similar faults the T762 is high it appears to be a receiver to steer clear of. If NAD can't help then I doubt anyone else can.

Reply to
Ross Herbert

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Hi I am an authorized Nad Tech, i may be able to assist. if you have replaced the 5.1v zeners D716,D718 you must change the electro C724. also these amps have many dryjoints on the frontpanel PCB and also on the main board, check to see if the DSP board is not shorting to chassis it has two screws at the top , the bottom of the board is fixed via two bent chassis clips if the rubber spacer has fallen off that holds the board above the chassis the board will short to ground, check the DSP for all voltages you can reference these by reading the printed overlay on the board were the cables enter, also there has been good upgrades to the firmware to fix many of the problems with this amp you may find it a good idea to upgrade the firmware. if you need any schematics i can help just drop me an e-mail. Regards Greg

Reply to
service

Hi Greg,

Have you ever heard of an NAD model 8100 active speaker system? It's a biamped, ported box with 8" woofer/.75" tweet. The active electronics consist of a pair of TAD 2030a chip amps bridged for the lows and a single 2030a for highs.

I got these, sans drivers, and retreaded with NOS Polk units I had. They sound pretty good, but they require tons of level (couple of volts) to get them to turn on. The turn-on relay is pretty obvious on the board, so I could just jump that and add a power switch, but I wonder if I could find a schematic and increase the sensitivity.

Also there's a 'black box' on the board, the function of which I can't determine. It's an encapsulated module with no markings, about 1.5" x

2.5 x .5" high.

Google is absolutely no help....

jak

Reply to
jakdedert

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