I have a NAD T 773 receiver and it makes a loud sound like "bang" and shuts down completely. Could not operate from remote or front of unit. Red light upper left corner of unit came on. Powered down from front of unit and unplugged for a few minutes. Plugged back in and started unit with the remote and it turned back on. Sound was very bad so turned unit off with remote and back on again and sound was ok. This happened a few days ago for the second time and do not know when it will happen. Unit is enclosed and nothing is around or on top of it so there is good air movement. Unit is still under warranty but a massive pain to unplug all and replug again. Could it be a overheating problem? Should I take it in for service? Let me know what you think.
You said Unit is enclosed!!
Does that mean it is inside something?
Receivers & Amps need to have a clearance above them so air can circulate, otherwise you'll have an overheating problem.
You also might have some of your wires crossed which will cause the Amp to shut down. Look at all your connections and make sure they're correct, including speaker wires.
No fix to this problem. When my T763 had the same symptoms I left it with the dealer who sent it on to service. It ended up being scrapped. So I'm afraid this is the end of your receiver unless your techies are better than the ones who worked on mine.
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There is no seperate fuse but it seems likely that the left side preamp or the power amp section had opened up a fusible resisitor that could have shut the section.
Now the only way out is to take a voltage or signal test with the right - working- channel as a reference . Please attempt only if you are familiar if not it will end up with further damage as the sections are very delicate. Testing with a signal will confirm the faulty section to narrow down your search.
Let's distill this down to its simplist configuration. FM source, stereo.
BTW, a search for NAD 440 only brings up a C440 >>>Tuner<<, no receivers. Are you sure about that model number? The only receiver model numbers with x40 on the NAD website are the C340 and C740, neither of which has a link to a manual (go figure). I have the C740 manual, so I'll use it for a loose reference.
If it still does what you're describing in a basic configuration and the volume control seems to affect it like you belatedly mentioned, I'd suspect a noisy volume control or some other control in the receiver (like a rarely used Tape Monitor switch) that is always there in the circuit but may have oxidized contacts and responds sometimes to burn-through.
Set the volume at a medium setting and repeatedly operate every switch, knob and button (one at a time) to gauge its effects on the sound. You may find one is the culprit. Then it's a matter of accessing it for a shot of contact cleaner.
If you have jumpers between Pre Out and Main In, it might be a good idea to reseat them, too.
If it's not happening when your speakers are disconnected, your problem is not in the receiver, it's either a wire touching at the terminals on the rear of the receiver, or a bad voice coil or crossover in your speaker. If you re connect the speakers and it immediately cuts out, disconnect all speakers and reconnect one by one testing the receiver each time until your receiver shuts off or remains on with all wires connected and you've fixed the problem. If it cuts out, disconnect the problem speaker at the speaker and test again. If it stays on, problem is in the speaker, if it still cuts out, problem is in the wire. Hope this helps. If you need further help, post a comment and I can help you troubleshoot some more.
Your problem is a common symptom of loose connection or cold solder and cleaning problem this is the main caused of no sound or automatic shut off for how many seconds..Cold solder issues - each component is soldered into small holes on the printed circuit board which in turn connects said component to the other components. Due to time, heat, use, some solder joints would be cracked or loose. It is possible that the cold solder is still minimally connected (hanging by a thread). When the receiver turns on heat would be generated which would be sufficient to further loosen up the solder joint to the point it no longer provides electrical contact. Jarring the unit creates movement inside enough to re establish the contact, sometime good enough sometimes not enough. Again, since the unit still operates (sometimes) then it is highly probable that there are no defective components. As you have surmised, it is possibly a loose connection, solder joints are "connections" except that molten soldering lead is used to attach/connect the component to the board, "loose connection" in this sense is equal to "cold solder". Again on the assumption of no defective parts, then seeking a more experienced buddy for the soldering might be to your advantage. This is of course in addition to the possible electrical hazards when repairing.... Good luck: