so ive been chasing this one for a while now and its starting to drive me nuts. got my IC-7300 probably 4 years ago and it was flawless up until a couple months back. what it does is starts out fine, full 100w into my dummy load, but after maybe 5 or 10 minutes of operating it starts pulling back power on its own. doesnt throw any fault codes or anything, the ALC looks normal on the scope display, just... less power coming out. like it'll drop to 60-70w and just sit there. let it cool down for 20 minutes and it comes back to full power again.

my first guess was the PA transistors running hot but i pulled the top cover and stuck a thermal probe around and nothing is getting crazy hot, the finals look fine. someone on another forum suggested maybe the LPF relays but i havent gotten that far yet. i did recap a kenwood once but the 7300 feels way more involved to get into.

anyone dealt with this specifically on a 7300 or similar ICOM? wondering if this is a known thing before i start throwing parts at it.

had something similar on mine a while back and it turned out to be the PA bias drifting with temperature. the 7300 uses a thermistor to compensate the PA bias but if that thermistor isnt making good contact with the heatsink anymore the circuit sees the wrong temp and pulls back drive to protect itself even when the finals arent actually that hot. its kind of a known-ish issue, not super common but not unheard of either.

before you go deep into it, worth doing a firmware check if you havent already, icom pushed a couple updates that touched the power management stuff. also id look at the PA board connectors, the one that feeds the bias circuit in particular. i had a connector that looked fine visually but had a pin that wasnt seating right and reflowing it fixed a similar intermittent issue on a different rig. the 7300 isnt too bad to work on once you get the covers off honestly, just take photos before you disconnect anything.

might be worth just logging the temp readout from the menu while you're transmitting and watching if it climbs faster than it should. the rig does have internal temp sensing and if something is off in how its reading it you'd see it reflected there. i think its in the set menu somewhere, radio temp display.

also dont rule out the power supply side either, if its a switching supply with some age on it and the voltage is sagging slightly under load that can do weird things. i chased a fault like this on an older TS-590 for two weeks before i noticed my astron was putting out 13.2 instead of 13.8 under load, not enough to cause obvious issues but enough to mess with the power output stability.