so ive had this 7300 for about 3 years no problems then last week i was running some digital and noticed the ALC was acting weird, output dropped off and now im sitting at like 18-22w max no matter what i do with the RF power knob. tried a factory reset, checked all the menu settings, ran the internal tuner through its paces, nothing. the SWR on my antenna side is fine, checked it with an external meter.

what gets me is the ALC meter on the display barely moves even when im supposedly at full drive. like the driver stage isnt seeing the signal right or something. ive done some digging and a few people mention the driver transistors on these can get cooked if you run them hot for too long on FT8 but i wasnt being crazy about duty cycle, had it at 50w and running maybe 30-40% duty cycle.

anyone cracked one of these open for a similar issue? wondering if its worth me trying to scope the driver output before i send it out somewhere. i have a decent bench setup but icom's service manual for this one is a bit sparse in some areas.

yeah this sounds like it could be the finals or driver stage but honestly my first suspicion on the 7300 when i see that kind of flat output ceiling is the PA bias drifting. there's a trimmer on the PA board and if it's drifted or the temp compensation is off you'll get exactly what you're describing - low and flat with the ALC barely reacting because it's not even getting enough signal to clamp down on.

before you dig into transistors i'd check the bias voltage on the PA stage with a meter. should be around 4-5v quiescent if i remember right, been a while since i had one on the bench. if that's way off then you might just need to readjust it, there's a procedure in the service manual although like you said it's not exactly detailed. if the bias looks right then yeah driver transistors start being more likely. RD70HVF1 is the final stage on those and they're not cheap but they're available.

also - did you check for any DC offset on the output? sometimes when a transistor is starting to fail you'll see a small DC component leaking through and that'll cause all kinds of weird ALC behavior.

i had something similar on my 7300 except mine was only happening on 10m and 6m. turned out to be a bad solder joint on the LPF relay board, the switching wasnt completing cleanly so it was basically running through the wrong filter path or partially open relay. totally different symptom pattern than yours but just throwing it out there because that board is worth a look while you have it open anyway, those joints arnt great from the factory in a few spots.