Originally Posted by KidHorn
So how does the overheating protection work?
The primary points are covered in UL Standard #60065, this covers the electrical components, switches, relays, transformers, plastics and wire/insulation types. A typical AVR will use various protection schemes these include voltage limiters, current limiters, low impedance sensors as well as temperature sensors located on the heat sinks and power transformer. In the UL standards a max temperature (85 degrees C) is listed and if exceeded one of the temperature sensors kicks in which may reduce or terminate
the voltage drive to the output stage. Also a similar scheme is used to protect the power transformer/AVR and/or respective component from destroying itself and becoming a warranty liability. In the earlier days fuses were frequently used but now available are smart
processors that includes temperature intelligence @ an affordable cost. The weakness of the fuse is that it is too slow
to react to a trouble fault, and if blown an expensive trip to the service center is required..
A key point for any consumer electronic component is reliability
be it an AVR, Blu-Ray Player, Sat Tuner, HD Display, PC... Is to keep its average operating temperatures within a controlled range. Thats why every AVR brand specifies in their Quick Start Guides & Operation Manuals to have at least 4" of free-air clearance for the L/R and top covers. Unfortunately today often the user ignores this point and has reliability issues due to overheating. Also it is common for the user to buy an entry-level product and overdrive its amplifiers and/or connect low impedance/sensitivity loudspeakers which can spell trouble...
Just my $0.02..