so this has been driving me absolutely nuts for the past three weeks. i picked up a used 7300 from a guy at the club swap meet, worked fine for about two days then started doing this thing where it just randomly drops to like 5-10 watts output mid-transmission. no warning, no fault codes, SWR looks fine on the meter, and then sometimes itll come back on its own after a few minutes. sometimes not.

already pulled it apart and swapped the PA board because that was the obvious suspect and honestly i had a spare from a parts unit anyway. no change at all. i scoped the ALC line and its not going crazy or anything, voltages on the driver stage look normal to my eye. the finals are running warm but not scary hot. im starting to wonder if its a thermal issue somewhere upstream of the PA or maybe something weird with the RF sensing circuit but im kind of grasping at straws at this point.

anybody dealt with this specific failure mode on one of these? the icom service manual is actually pretty decent but its not exactly chatty about intermittent stuff like this.

had almost the exact same symptom on mine about a year ago and it turned out to be a cold solder joint on the driver board, not the PA at all. tiny hairline crack that you basically couldn't see without a loupe and good lighting. the joint would open up as the board warmed and then sometimes reseat when it cooled down. i found it by very carefully reflowing suspicious joints around the driver transistor area while watching the output on a dummy load. took me an embarrassingly long time to find it but once i reflowed that one spot it never happened again. worth going over those joints carefully before you dig any deeper into the RF sensing stuff.

not sure if this is related but i've seen a few 7300s with dodgy ribbon cable connectors causing weird intermittent behavior, not exactly power drop but odd stuff. might be worth reseating all the internal connectors while you have it open. also what power supply are you running it off? i know it sounds basic but ive seen a supply that measured fine under light load completely fall over at 100w and the radio does all kinds of strange things trying to compensate. just throwing it out there.