My Harmon Kardon AVR 500 sound doesn't work, I disconnected speakers, re connected & reset protection. Nos ound not even on test mode

Very little information on it apart from that you need to take it for professional service as mentioned at JustAnswer by a tech..

https://www.google.com/search?q=Harmon+Kardon+AVR635+protection+mode

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Fault in one or more channels.
Take your DVM and test for short circuits or take it to an HK repair shop.

I would try disconnecting the speakers, then turn it on. If protect still shows with no speakers connected, then it needs to go to the repair shop- Might be a blown power transistor.

Disconnect speakers and wires. Bad wiring or defective speakers may be loading the amp down and causing the protection circuits inside to disconnect (no sound). If the HK is heating up (beyond what you perceive as normal) with no wires or speakers connected then you have a problem requiring expert repair.

Check all speaker wiring for shorts, if okay! there is a problem in the audio output stage of the unit or the protection circuit is not working properly. I would suggest a pro to evaluate.

Disconnect all speaker connections and rca cables. Leave power, ground and remote wires intact. Try turning on again. If you still have a protection light your amp is faulty. Hopefully you have warranty. Double check all connections .A thumbs up would be greatly appreciated if this answer is helpful to you. Worth fixing.

Use the help function on your Logitech remote.
Need more information on specific problem to go much further.
Check for tight speaker connections on back of receiver.
Some units have fault sensing; causing 'drop out' preventing A/V receiver from turning out. Typically this is characterised by a clicking sound after receiving an IR signal.
Using high volume levels can affect speaker connections, especially at the back of the A/V unit connectors and banana speaker wire connections.

It is either a mismatch or improper ground connection.
Try correcting it by putting a ground line at your AVR
254.

plug eash units sound in red whites from dvd tv main out the set speaker wires in place front ch a ok turn it on make sure ch a speakers on only select corect video input dvd ect turn it up