so this has been bugging me for a couple weeks now. my 7300 is running great on pretty much every band except 20m where it seems to top out around 18-22 watts no matter what i do with the power slider. all other bands hit close to 100w no problem. ALC looks normal, RF gain is where it should be, tried different antennas and feedlines in case it was some weird reflection thing causing the radio to pull back but same result.

i did a factory reset thinking maybe some setting got borked but nothing changed. the radio doesnt throw any error codes and the SWR on 20m is fine, like 1.3:1 on my dipole. temps look normal too, no thermal shutdowns or anything like that. its not the antenna side, i can run another radio on the same feedline and get normal output.

started looking at the finals but before i crack anything open i wanted to see if anyone has seen this specific thing where its just one band thats affected. feels more like a driver stage or a filter issue to me but im not an RF tech so take that with a grain of salt. anyone dealt with this?

yeah that pattern — one band low, everything else fine — usually points to the LPF relay or the filter switching itself rather than the finals. on the 7300 the low pass filters are switched by relays and if one of those relays has a dodgy contact it'll pass signal but with extra loss, and that loss shows up as reduced output. 20m shares a filter with... i want to say 17m if i remember right, might be worth checking whether 17m is also slightly low or if its just 20.

if 17 is also affected that kinda confirms it. the fix isnt too bad if youre handy with a soldering iron, the relay can be reflowed or replaced, but honestly given the 7300s price point id be on the phone to Icom service first to see if this is covered under anything. theyve been decent about stuff like this in my experience.

dont rule out the PA board entirely though. ive seen cases where one of the finals starts to degrade and the bias shifts in a way that only shows up under certain drive frequencies. not super common but it happens, especially if the radio has any hours on it running digital modes at high duty cycle. the 7300 is popular for FT8 and people run those things at 50-60w for hours straight which is hard on the finals over time.

the relay theory is more likely statistically but worth checking output with a scope if you have access to one just to see the waveform shape on 20m vs a working band. if its clean but just low amplitude thats more relay/filter, if its ugly or clipping thats more PA side. just my two cents, not a radio tech myself but ive gone down this road with an older FT-991.