so this has been driving me nuts for about three weeks now. the radio works fine when i first key it up, receive sounds great, sensitivity seems normal. then somewhere around the 15-20 minute mark the receive just... drops. like signals that were S7 are suddenly barely above the noise floor. transmit seems fine the whole time, SWR reads normal, put out full power, but nobody can tell anything is wrong on my end.

then after maybe 5-10 minutes of being deaf it just comes back on its own. no reboot, no nothing. just starts hearing again like nothing happened.

my first thought was a thermal issue somewhere, like a component that's marginal and drifts when it warms up. i pulled the top cover off and ran it with a fan blowing across the board and the problem still happened, though maybe it took a little longer. wasnt a controlled test though so hard to say for sure.

radio is about 4 years old and out of warranty. i did have it outside in the car for a couple summers so maybe some heat damage at some point? anyone dealt with anything like this on the 7300 or similar rigs?

thermal intermittents are the worst to chase, you're right to suspect that. the fan test not fixing it doesnt rule it out entirely because the component that's failing might be getting heat from the board itself not ambient air. classic move is to use freeze spray in sections while it's in the failure state and see if receive pops back — if it does you found your neighborhood at least. i've done that on a couple HF rigs with dodgy preamp stages.

on the 7300 specifically, ive read a few threads on other forums about the RF unit having some QC variation from icom on that generation. not saying it's a known defect exactly but some guys have had the rx amp section act up. if you're comfortable with SMD work it might be worth pulling the RF board and reflowing anything that looks even slightly cold. four years plus car heat is enough to stress those joints.

also worth checking — does it do this on all bands or just certain ones? that would tell you a lot about where to look.

had something similar on my old 746 pro, turned out to be a relay. the rx/tx switching relay was intermittently not returning to rx position fully after transmitting. your situation sounds a bit different since you said it happens without transmitting but worth keeping relays in mind as a suspect. they're cheap and easy to overlook.