so ive been scratching my head on this one for about two weeks now. my 7300 is doing something weird where on 40m specifically the output power drops to maybe 20-25 watts at full drive, every other band is putting out close to 100w no problem. ALC looks normal, the display isnt showing any faults or PA temp warnings, and it doesnt seem to be heat related because it does it cold too right from startup.

i already went through the obvious stuff, checked the antenna, tried a dummy load, reseated the connectors i could get to without fully disassembling it. swapped coax. still the same thing. its like the finals are just... unhappy on that specific band and i cant figure out why. has anyone seen this on a 7300 or had to dig into the PA board on one of these? im comfortable with SMD work but id rather not go poking around blind if someone has a schematic note or a known failure point on that board.

yeah this actually sounds like it could be the LPF switching relay for 40m. the 7300 uses switched low pass filters for different band segments and if the relay contact is dirty or has developed high resistance it'll eat your power on just that band. i had almost the exact same symptom on a friends radio except his was 20m. pulled the board, reflowed the relay solder joints and cleaned the contacts and it came right back. its a pretty common failure point on these radios after a few years especially if the radio has seen any humidity.

if you have a service manual look at the LPF unit schematic, i think its around page 6-4 or so in the icom doc. the relays are through-hole so theyre not too bad to reflow even without hot air. worth checking before you start condemning finals anyway.

could also be worth checking if the band data lines are all seated properly, i know thats kind of a long shot but i had a weird intermittent power issue on mine turned out to be a ribbon cable that wasnt fully clicked in after i had opened it up to clean the fan. probably not your issue since yours is band-specific and consistent but just something to rule out i guess.