And the issue is back! Kind of.
It doesn't trigger Audyssey any more, but just randomly goes to protect mode a couple of times a week. It can trigger after two minutes of listening to stereo music or two hours in to a movie. When this happens the power light is blinking rapidly and protection history shows "DC". Low or high volume, cool or warm device, doesn't matter.
Of course I've gone through all the wires, added a fan for cooling etc. It's hard to troubleshoot because the problem comes up so randomly.
Frustrating. The earlier owner only used this amp in a stereo setup and had no problems. And my problems started a few months after purchasing this amp second hand.
Sounds like the amp section has developed a fault causing excessive dc at the output. Have you checked the dc offset with a multimeter yet?
One thing to try is to see if the preouts are working, using preamp mode. If the power amp section is in fact failing, you would have to send it out for troubleshooting/repair, or just use the unit as a preamp/processor if you don't want to go through the trouble of going through the repair process and/or avoid the cost if it is out of warranty. Or, if you have the knowledge/skill yourself to troubleshoot/repair then go for it.