so this has been driving me nuts for a couple weeks now. picked up a used 7300 from a guy at the club swap meet, seemed fine when i tested it briefly at his table, got home and after maybe 20 minutes of actual use on 40m the output just dropped to almost nothing. like im getting maybe 2-3 watts on a good day when it should be pushing 100.

the weird thing is it doesnt trip the protection or throw any error on the display. SWR looks fine on a dummy load. driver stage seems okay-ish based on what im seeing at the rf board but honestly im not super confident in my diagnosis there. i pulled the lid and nothing looks visibly burned or obviously wrong which i guess is either good or bad depending.

before i go ordering finals and regretting it, has anyone seen this specific symptom on the 7300 where it just quietly loses output without actually faulting? wondering if its a bias issue or maybe the ALC is doing something weird. i have a scope i can use but i want to make sure im probing in the right spots before i poke around in there.

had something similar on a 7300 about a year back, though mine did eventually throw the protection. before you go assuming finals check the ALC line first — theres a known thing where the ALC voltage can get pulled low by something upstream and the radio just quietly backs way off on power thinking its protecting itself. its not a super common fault but ive seen it trip people up because everything looks normal on the surface.

also worth checking is whether the output drops equally across all bands or just 40. if its only one or two bands that changes the picture considerably. the finals on these are actually pretty robust and usually when they go they go in a more dramatic fashion, not this slow quiet fade you're describing. i'd lean toward bias or ALC before condemning the output stage. pull up the service manual and check the bias adjustment procedure, the trimpots can drift especially if a previous owner was poking around in there.

swap meet 7300 with mystery history, yeah that's always fun. did the seller say anything about why he was moving it? not accusing anyone of anything but sometimes people offload stuff right when a problem is starting to show up and they know it.

anyway the bias drift thing the other guy mentioned is legit, that would be my first check too. also dont overlook the possibility of a cold solder joint somewhere on the driver board, these things travel around and get bumped and sometimes connections that were marginal get worse over time. a careful visual with decent magnification and maybe some gentle pressure on connectors while watching the power output could tell you something.