I have an old Marantz SR4200 AV 5.1 amplifier, bought via 'AV Forums' for £100 back in iirc 2004 (that was originally purchased in RS in Leeds in 2002 for £300). And it's still going strong! 🤞 

Out of the blue, I started getting an intermittent PROTECTION message on the LED screen, suggesting some sort of overload. The amp would switch off, but could be turned back on again and would work just fine (for a while longer).

The message doesn't appear in the manual, so it's unclear whether it was the INPUT signal that was too high, or something wrong with the OUTPUT to the speakers, or indeed something completely unrelated like overheating.

The tripping happened with various movies/TV, usually during the noisiest scenes, so turning down the sub seemed to help but not cure (LFE to -10 and sub to -5). Googling, there are all sorts of suggestions, including dry joints that might need soldering, and the addition of a new cable to bypass the protection circuit (clever! This series of amps still gets a lot of love).

ANYWAY, it turned out to be a very simple fix, that scarcely gets a mention online ...

A stray strand of copper cable on my FR speaker binding post was shorting. And I guess that vibrations from the sub had made the short during the loudest scenes!

So my amp lives on, hopefully for another couple of decades ...