so this has been driving me absolutely nuts for the past few weeks. my 7300 randomly drops out mid-transmission, like i'll be talking and the ALC just goes flat and the TX indicator stays lit but no RF output. happens maybe once every 20-30 minutes, sometimes more. sometimes it'll go hours without doing it.

i thought at first it was my mic but i swapped to a different one and same thing. checked the PA temp and it doesnt seem to be thermal - it does it even when the rig has been on for only 10 minutes and is barely warm. i had it on the bench and ran it into a dummy load at 50W for about 45 minutes and couldn't reproduce it, which is the most annoying part.

connection on the back looks fine, coax is solid. im wondering if its maybe something on the driver board or a bad solder joint somewhere that only opens up under certain RF conditions. anyone seen anything like this or have a idea where to start poking around?

had almost the exact same thing on my 7300 about a year ago. for me it turned out to be the ACC socket on the back - something was triggering the external ALC line and pulling TX down. i wasnt even using that socket but the contacts were dirty and i guess were floating around enough to cause issues. just putting a shorting plug on it fixed it immediately. probably not your issue if you've already ruled out external stuff but worth 2 minutes to check before you start pulling boards apart.

also, have you checked the TX inhibit line? theres a pin on the ACC connector that if it sees voltage will kill TX. i've seen people chase this for ages not realizing something was feeding into it.

could be a cold joint on the finals or driver stage yeah. those icom boards are generally solid but ive seen a few where the PA transistor legs have a hairline crack that only opens when there's RF current flowing through - heat doesn't necessarily reproduce it, it's more the actual current path. if you have a bench supply and can hook up a current probe while transmitting that might tell you something. or honestly just a good magnifying glass and a bright light over every joint on the PA board is where i'd start. reflowing the whole PA section isnt a bad idea anyway on a rig thats been used a while.