so this has been driving me nuts for about three weeks now. i picked up an ic-7300 off a local ham who said it 'just needed some work' which should have been my first red flag honestly. the radio came to me putting out maybe 8-10 watts on a good day no matter where the power knob was set, all bands same story.

i figured finals were shot so i pulled it apart and replaced the RD70HVF1s, checked all the bias points, set them per the service manual, buttoned it back up and... still the same thing. maybe 12 watts now if im lucky. ALC looks weird on the scope too, it kind of slams up immediately even at low drive levels which makes me think somethings still wrong upstream of the PA stage.

before i go tearing into the driver stage i wanted to ask if anyone has seen this specific pattern before. the receive side is perfectly fine, sensitivity seems normal, no obvious damage anywhere on the boards. just this weird low power output with the ALC behaving badly. im wondering if its a bias issue i missed or if theres something going on with the low pass filter board or maybe even a bad solder joint on the driver transistors.

yeah the ALC slamming like that is your clue, i had almost the exact same symptoms on a friends 7300 last year. turned out to be a bad solder joint on one of the coupling caps between the driver stage and the finals. visually it looked totally fine but when we reflowed it the power came right back up. also worth checking the PA bias trimmer -- on ours it had drifted way out of spec and was causing the ALC loop to go haywire trying to compensate. measure the quiescent current on each device individually and compare them, if ones way off from the other that tells you something. the service manual bias procedure is a bit vague imo, you really want both devices tracking closely or the ALC never settles properly.

dont overlook the directional coupler on the RF board, ive seen those go flaky and give the ALC circuit garbage feedback which makes the whole power control loop act exactly like what youre describing. its kind of a weird failure mode and easy to miss if youre focused on the obvious stuff like transistors and bias. poke around on the ALC voltage line while youre driving it at low power and see if its actually stable or bouncing around.