so this has been driving me absolutely nuts for about three weeks now. my 7300 started doing this thing where it'll just drop to zero power output mid-over, like not gradually, just suddenly nothing. SWR meter on the radio still shows movement so it thinks its transmitting but the wattmeter on the coax side reads flat zero. happens on every band, doesn't matter if im doing 100w or dialing back to 25w.

first thing i did was swap coax, swap antennas, tried into a dummy load. same thing. so its definitely the radio. pulled the covers and visually everything looks fine, no obviously burnt components, no smell. been poking around the PA board and the low pass filter section but honestly i dont see anything obviously wrong and i dont have a good enough scope to really dig into the RF path properly.

before i send it off to icom i wanted to see if anyone's run into this specific symptom. the random part is what gets me — it can go 45 minutes without any issue then just die for a few seconds and come back. sometimes it stays dead until i cycle power. ALC looks normal right up until it cuts out. anyone seen this?

that intermittent behavior with the ALC looking normal right up to the cutout is interesting. had something similar on an older 7200 and it ended up being one of the driver transistors getting flaky when it warmed up — thermal issue basically. the PA finals were fine but one of the drivers would just stop cooperating once it got to a certain temperature. you could actually predict when it was going to happen after about 20-30 minutes of operation because the case would be warm by then.

worth checking if there's any correlation to heat on yours. let it sit powered on for a while with no TX, then start transmitting and see if the timing of the dropout matches up with thermal soak. if it cuts out faster on a warm day that's probably your answer. icom's service manual has the driver stage laid out pretty clearly and the transistors themselves arent expensive if you can solder SMD, which on a 7300 you need to be comfortable with anyway.

also check all the coax connectors inside the chassis. i know you swapped external stuff but the internal PL-259 to board connection on these can develop a hairline crack that only shows up under RF load. i've been burned by that before.

cant say ive seen exactly that but my first instinct would be the ALC feedback loop before i go digging into the PA itself. if the ALC circuit is sending a weird signal the radio will throttle output to nothing without the finals actually being bad. might be worth scoping the ALC line if you can get a probe on it during one of the dropout events.

also what firmware version are you on? there were some weird TX issues reported on older firmware, i dont remember the specifics but it might be worth a search on the icom users group reflector before you crack it open further.