Originally Posted by harrybnbad
That was short lived...
Back to the red flashing light.
Looks like (1) ASO/DC PROTECTION: Flashes at intervals of 0.25 seconds lit, and same off...
Sounds like something to do with that DC 17
DC 17 means that the AVR has gone into Protection Shutdown mode 17 times - because of abnormal DC current in one or more of the power amplifier stages.
There are nine separate amplifier boards in the 4520, looking from the front panel - there are four on the right-hand side, and five on the left-hand side.
Each group of amplifiers have two multi-way connectors providing signals, control lines, and power. The upper two sets of cables are the pre-amp signals.
If the pre-amp outputs are NOT connected fully to the amplifier inputs - an excess DC current will flow in the affected channel, triggering the shutdown.
Checking the multi-way cables on each side of the unit may identify the issue.
These two pictures show the cables concerned - with my own custom made cables connected to top connectors in each case.
You may be able to see the connectors without taking the lid off - if you shine a torch through the air vents that run along the unit sides.
Edit : Just added another Service Manual picture.
Remotely, this is the best I can offer - hope it might help, regards, Mike