I have a Yamaha HTR-5550 and has performed very well up to recently when it shut-off after an hour of operation. If I wait a while it will restart. I always operate the receiver at very low level and I can't believe there is overheating. There must be some kind of electronic problem. Could somebody give me some indication of what could be the problem/part to be replaced.
If you place your hand over the unit when it shuts down (no need to touch), is it hot? If so there is something very wrong, especially if you don't run it at high volume. With the amplifier switched off, check the speaker connections. It's possible you may have a minor or incomplete short circuit which is draining power from the amplifier and causing it to overheat.
If that all checks out, try disconnecting the speakers and switch on with no signal running through it. Does it switch off after an hour (and is it hot)? If so there is definitely something wrong with the receiver.
If it doesn't switch off and has not gone hot, it could be a problem with one of your speakers. one of them could have failed in some way. Try connecting one speaker and with no signal leave it on for an hour and see if the amplifier switches off. If it does, it's the speaker or the cable. If it doesn't try the other speaker on its own again on the same channel. If there's no problem, switch channels. If the problem occurs on one speaker, try the other and if the problem occurs on both speakers, then the problem is with that channel of the receiver.
How are your components arranged. Does the receiver have room to breath. Nothing on top of it and several inches around it. The Yamaha's do shut down without adequate ventilation.
If the receiver is in a situation that might endanger its future operation, they will hopefully shut down. If there are part(s) failures, they will shut down. And they might not even get hot before they do so.
FG, try what Frank suggests. If the receiver shuts down with no load, there is a problem with the receiver. If it continues to run without a load, there is a problem that is being placed on the receiver when you connect speaker cables.
If there is any reason to suspect something has changed before the problem first made itself known - changing a cable on another part of the system, pulling the receiver out to clean or rearrange cables, etc. - you should check all your cables and connections. A single strand of loose wiring between speaker connections and the chassis of the receiver could be causing your problem. If a cat or other animal has the ability to reach the cables, you might have a frayed/damaged cable. Be very careful when re-dressing your cables after your no load experiment.
If the unit doesn't shut down under no load conditions, connect a single pair of speakers at a time (front, then rear and then center) with a waiting period between connections to check for possible problems in the cables.
If the receiver shuts down without a load (no speaker cables connected), you have internal problems with the unit and no one here should be foolish enough to suggest you open the receiver and try to complete a repair yourself - even if we could tell you what part needs replacing. Take the unit to an authorized Yamaha repair center. If the receiver is no longer in warranty, ask for an estimate of repair costs before giving the OK to proceed. Do not remove the cover of the receiver yourself to poke around inside, there are dangerous and possibly lethal voltages that exist in the receiver even when it is disconnected from the AC outlet. Let a technician do the diagnosis.