so ive been chasing this one for a couple weeks now and its driving me nuts. my 7300 is putting out maybe 30-35 watts on 40m at full drive but everywhere else its doing the full 100 no problem. checked the ALC, messed with the RF power setting thinking maybe it had gotten bumped but nope, everything looks normal on the display. SWR on the band is totally fine, dummy load confirms it, so its not the antenna side.

i opened it up and had a look but didnt really see anything obvious, no burnt smell, caps look ok to my untrained eye. im wondering if its one of the finals getting weak or if theres some driver stage that handles 40m differently. does anyone know if the 7300 has band-specific driver circuitry or is it all shared? havent pulled the service manual yet but i probably should.

radio is about 4 years old, maybe 600-700 hours on it, nothing crazy. just started doing this out of nowhere one morning.

yeah pull the service manual, its actually pretty readable compared to some of the older icom stuff. the 7300 does share the final PA board across bands but theres bandpass filtering and some switching that happens per band so theres definitely places where a 40m specific fault could show up without affecting the others.

first thing id check is the LPF relay for that band. those relays can get flaky and cause weird power issues that dont always look like a relay problem. you can sometimes hear a faint click that doesnt sound quite right when it switches but its hard to tell honestly. theres a test point procedure in the manual where you can measure the drive level going into the PA and compare it to what the PA is actually seeing - if drive looks good but output is low then youre probably looking at the PA board itself or the relay. if drive is already low then its upstream, maybe the DSP/modulator section though that would be weirder.

i wouldnt assume the finals are dying yet, partial failure on one band with the others fine is more often a switching or filtering issue in my experience. finals usually take everything down together or at least affect adjacent bands.

had something similar on a 746 pro years ago, different radio obviously but same kind of symptom - one band just decided to be lazy. turned out to be a cold solder joint on one of the LPF board connectors. just enough contact to pass signal but not enough to handle full current. resoldering the whole connector fixed it and it never came back. worth looking at the connectors with a magnifying glass or loupe if you havent already, especially anything that plugs into the main board.