so my 857d just stopped receiving on 20m yesterday, transmit seems fine though. other bands work ok. already checked the obvious stuff like attenuator settings and filters. antenna analyzer shows swr is good. anybody seen this before? im thinking maybe the front end but not sure where to start

had something similar happen to my 857 couple years back. turned out to be a bad diode in the rf board, think it was d1015 or something like that. you getting any noise at all on 20m or totally dead? if its completely silent might be worth checking the bandpass filters first before digging into the mixer circuits

Check your ALC settings too - I know it sounds weird since you're talking about receive but I've seen rigs do strange things when the ALC feedback circuit gets wonky. Also try doing a full reset, sometimes these rigs get their brains scrambled and a factory reset fixes weird band-specific issues. Worth a shot before you start pulling boards apart.