The Denon AVR-2310 was $30. The symptoms were no audio, but all else works fine. I tried a CD and DVD, the display indicated the change in detected audio formats, but there was no sound. I would have tried the tuner but for some reason there doesn’t appear to be a way to change source to the tuner unless you have the remote. I removed the top cover and used an air compressor to blow all the dust out. I read online to pay particular attention to the headphone jack when there is no audio. Put it back together and it started with no issues. Watched a few movies and the sound was excellent.
I do note it wasn’t very loud until I turned all the filters off like Dynamic volume, Dynamic EQ and Audyssey off. Also, during testing the setup mic wasn’t used to optimize the speaker output.
I have another Denon – an AVR-2308 (I think) which has similar issues but more extreme where it blows a fuse when the amps are powered up. That amp is a work in progress and might be a write off.
Cheers