so this has been driving me nuts for about three weeks now. my 7300 will just cut out mid transmission, sometimes after 30 seconds sometimes after like 8 minutes, completely random. when it drops it doesnt shut off fully, the display stays on, audio comes back on receive, but TX power goes to zero and the ALC is doing weird stuff. key up again and sometimes its fine, sometimes it just does it again immediately.

before anyone asks — yes i checked the fan, its spinning fine. yes i checked the SWR on the antenna, running under 1.5:1 on 40m where this happens most. the PA finals arent getting crazy hot from what i can tell by feel on the case. i did a factory reset last week which changed nothing. power supply is an Astron RS-35M putting out a steady 13.8v under load, checked it with my meter while keyed up and it doesnt sag more than a couple tenths.

the part that has me confused is that it seems worse when the shack is warmer, like today it was maybe 75 in here and it dropped out four times in an hour. a few weeks ago when it was cooler outside it ran a whole contest session with no issues. thermal issue somewhere is my guess but i cant figure out where to start poking around. anybody dealt with something like this on a 7300 or similar SDR-type radio?

thermal problems that dont show up on the case temp are usually a dry joint or a component thats marginal and doesnt like heat expansion. on radios like that i usually start with a good look at the PA board connections and any surface mount caps near the driver stage, but honestly getting inside a 7300 without voiding stuff is a bit of a pain depending on warrenty situation.

one thing worth trying before you crack it open — run it with the top cover off and point a small fan at the internals. if the dropout frequency changes dramatically thats a pretty strong indicator youre chasing a thermal thing on a specific board rather than something like the protection circuit being flaky. also have you checked what the radio itself is reporting for temp? think you can see it somewhere in the menus, cant remember exactly where off the top of my head but it logs internal temp. might give you a baseline to compare against when it acts up vs when it doesnt.

had something vaguely similar on an older 706 years back, turned out to be a cold solder joint on one of the connectors between the RF board and the control board. wiggling the internal ribbon cables very gently while keyed up actually reproduced the fault which made it pretty easy to find. wouldnt necessarily expect the same on a 7300 but the diagnostic approach is the same — try to reproduce it and narrow down which board its coming from.

also worth checking the DC connector on the back of the radio itself, those can develop resistance over time especially if the radio gets moved around or the cable gets tugged. even a little bit of resistance there can cause voltage to sag right at the radio even if your supply looks fine at the terminals.