Pioneer VSX-923 - "FL OFF" error

[Halcyon]

Hi guys, I'm asking for a friend because he is too lazy and was going to throw this unit out.

He has a Pinoeer VSX-923 amplifier/receiver that shuts down shortly after power-on and flashes the FL OFF indicator and previously was also getting the "AMP OVERHEAT" error. Googling suggests that it's temperature or power supply related. I had a quick look inside but it's packed with boards and things. I couldn't see anything that was obviously a thermistor that could be bad. I should point out that the amp doesn't appear to be getting hot at all.

Does anyone have any experience repairing this kind of fault? EE-noobs here.

[floobydust]

It takes an incredible amount of patience to rip these apart and fix them. You will likely die in the avalanche of screws, at least for Onkyo's.

A real overheat can be from vents being blocked, a dead fan, shorted speaker wiring, or the idle current needs to be checked/adjusted if there is a hot channel. It's only 2mV of bias 8.5mA (measure at the 3-pin test header each channel has) which should not make a lot of heat.

The receiver seems to have 7 SMT thermistors on the PCB pads next to the output transistors that mount on the heat sink. 95-105 °C before it shuts down. They are wired-OR in two groups (RADI and TH? =radiator/heatsink for front channels and ? for the surround channels) so finding a dud  thermistor a little difficult but you could compare ohmeter readings between channels and see if they agree.

Try (not my words):
6. SERVICE MODE
6.1  TEST MODE - Detected protection history
During Standby mode, simultaneously press and hold “MULTI-ZONE ON/OFF” and “ENTER” keys for 5 seconds to enter this mode. Turn off the power to this unit by setting the main volume level to “---dB” and Multi-zone to “OFF”.  {tune up/down to scroll through list, fan test does not work}
DC Display number of times DC is detected.
OL Display number of times OVERLOAD is detected.
COM Display number of times COMBINATION is detected. (Detects DC and OVERLOAD simultaneously)
XPRT Display number of times Power abnormality is detected.
STMP Display number of times AMP overheat is detected.
DERR Display number of times Digital Power abnormality is detected.
... more diags

"Turning off the power or pressing the RETURN key returns to the normal mode. Pressing the RETURN key returns to the normal mode."