so this has been driving me nuts for a few weeks now. my 7300 will run fine, full 100w out, and then somewhere around the 20 minute mark it just starts pulling back power on its own. not all the way down, like maybe 40-50w, sometimes less. no fault codes showing up on the display that i can see. ALC looks normal before it happens, SWR is fine, feedline is fine, antenna hasnt changed.

at first i thought it was the finals getting hot and the radio protecting itself but the fan seems to be running fine and the heatsink on the back isnt even that warm when it happens. i pulled the bottom cover off and watched it do it once and nothing looked obviously wrong. no capacitors bulging, no burn marks, nothing smells.

i did notice the internal temp sensor reading climbs a little faster than i expected but idk if thats normal for this radio or not. anybody dealt with something like this before? wondering if its worth pulling the PA board or if im missing something obvious before i go that far.

had something similar on an older 7200 years back and it turned out to be a dried out thermal pad on the PA transistors — the pad had basically crumbled and wasnt making good contact with the heatsink anymore so the junction temp was spiking even though the heatsink itself felt fine externally. the protection circuit was doing exactly what it should, just wasnt obvious from the outside.

on the 7300 i'd check the thermal interface between the finals and the chassis heatsink before you go too deep. icom's assembly on that generation could be a bit hit or miss with thermal compound application from what ive read. not a hard fix if thats it, just a bit fiddly to get to. also worth checking if the APC circuit is doing anything weird — some guys have had the APC pot go flaky and cause similar symptoms but usually that shows up more erratically than what you're describing.

does it happen at the same power level every time or does it vary? asking because i had a 7300 that did something vaguely like this and it turned out to be a dodgy connection on the power supply side rather than the radio itself — voltage was sagging just enough under load after warmup that the radio was backing off. worth throwing a meter on the supply terminals while its running if you havent already, just to rule that out before you start pulling boards.