so this has been driving me absolutely nuts for about three weeks now. my 7300 will start a transmission fine, i can see it hit full power on the meter, but somewhere between 5 and 30 seconds in it just drops to basically zero output. like 2-3 watts maybe. the display stays on, the rig thinks its still transmitting, ALC looks normal-ish, but RF output just falls off a cliff.

what's weird is it only seems to happen when the rig has been on for at least an hour or so. if i key up cold it's totally fine. i've already reseated the finals heatsink connection and checked the fan is spinning, which it is. PA temps on the diagnostics screen dont seem outrageous either, usually sitting around 45-50C when it happens.

i did check the SWR and the antenna is fine, like 1.2:1 on 40m which is where i mostly noticed this. swapped coax just in case. same deal. honestly starting to wonder if it's a thermal issue somewhere other than the finals, or maybe a cap somewhere on the driver board going intermittent when it warms up. anyone dealt with anything similar on these rigs?

had something similar on an older 746 pro years ago, turned out to be a bad solder joint on the driver stage that would open up when the board expanded from heat. the symptom that gave it away for me was i could reproduce it faster by gently warming the board with a heat gun from a distance — not enough to damage anything, just enough to get it to the threshold temperature quicker. took me a while to find it visually but eventually spotted a cold joint near one of the bias transistors that looked totally fine under normal light but showed up under magnification.

with the 7300 id maybe start by checking if icom put out any service bulletins for this, they occasionally do for the more common failure modes. also worth pulling the bottom cover and just doing a slow visual with good lighting and a loupe. thermal intermittents are a pain because they don't show up when you most want them to.

not sure if this is the same thing but my buddys 7300 had a dropout issue and it ended up being the PA protection circuit triggering for no obvious reason, like a component in the protection circuit itself was drifting and falsely flagging an overcurrent condition. icom service center found it pretty quick apparently but it wasnt something you'd easily see without the right test gear hooked up during a live fault.

yours sounds more heat-related tho given the warmup time. does it recover on its own if you stop transmitting for a few minutes and then try again, or does it stay faulted until you power cycle?