I'm trying to repair a Denon AVR-X4500H home theater receiver. The fans over the heatsink stopped working and it overheated and shutdown into protection mode.
Having repaired audio amplifiers in the past, I focused my efforts on checking the power transistors (FETs) first and found one channel had both the "push" and "pull" FETs blown with a dead short between the source and drain. I replaced both of those and now all the FETs appear to be fine (around 0.5V in diode check between the source and drain in correct polarity, no volts reverse polarity) but the amp still turns off after 6 seconds. The service manual says that the it shutting off 6 seconds after turning on and flashing the power LED red with .5s on and .5s off = "DC Protection Mode" but doesn't give any more troubleshooting information.
Complicating matters is that the power amplifier module has the FETs mounted at the bottom, so you can't really check the voltages with the thing assembled. The bottom of the chassis basically blocks access to them and it only staying turned on for 5 seconds makes trying to take measurements pretty impossible as well.
Service manual (with schematics) can be found here: https://www.manualslib.com/manual/2798277/Denon-Avr-X4500h.html#product-AVR-X4500H
Having repaired audio amplifiers in the past, I focused my efforts on checking the power transistors (FETs) first and found one channel had both the "push" and "pull" FETs blown with a dead short between the source and drain. I replaced both of those and now all the FETs appear to be fine (around 0.5V in diode check between the source and drain in correct polarity, no volts reverse polarity) but the amp still turns off after 6 seconds. The service manual says that the it shutting off 6 seconds after turning on and flashing the power LED red with .5s on and .5s off = "DC Protection Mode" but doesn't give any more troubleshooting information.
Complicating matters is that the power amplifier module has the FETs mounted at the bottom, so you can't really check the voltages with the thing assembled. The bottom of the chassis basically blocks access to them and it only staying turned on for 5 seconds makes trying to take measurements pretty impossible as well.
Service manual (with schematics) can be found here: https://www.manualslib.com/manual/2798277/Denon-Avr-X4500h.html#product-AVR-X4500H