so ive had this 857 for probably 6 years now, bought it used off a guy at a hamfest and it's been rock solid until about two weeks ago. started noticing my signal reports were way down on 20m and when i finally put a wattmeter inline i'm only seeing about 8-12 watts out on a good day when it should be doing 100. the ALC looks normal on the display, no faults showing, and it receives fine. tried it on 40 and 15 and same deal across the board so it's not band specific.

already reseated the finals connector and checked the obvious stuff. PA supply voltage looks okay at the connector. wondering if this is a classic driver stage issue or if the finals themselves are going. haven't pulled the board yet because i keep second-guessing myself on where to probe first. anyone been through this on the 857?

had almost the exact same symptoms on mine a couple years back. turned out to be Q1024 on the PA board, one of the driver transistors. the finals were actually fine. the tricky part is the reduced drive makes it look like a final problem but if all bands are affected equally and the ALC is behaving normally, the driver stage is the first place i'd go. you can check bias voltage on the driver stage before you even pull the finals, saves a lot of headaches.

there's a service manual floating around on the Yaesu yahoo group archive or miklor's site has some of the board layouts. the bias trimmer for the driver is worth checking too, they can drift over time especially if the rig ran hot for a while. what's your heatsink situation like, does the fan kick on normally?

could also just be a dirty or intermittent PA relay contact. i know that sounds too simple but ive seen 857s do weird power output stuff from exactly that. worth spraying the relay contacts before you go too deep into the board. the relays on those rigs arent exactly military grade if you know what i mean.