so ive been chasing this one for about three weeks now and im starting to lose my mind a little. the rig receives perfectly, SWR meter on my antenna analyzer looks fine on the dummy load, but when i key up there is literally zero power output. not low power, not reduced power, just nothing. the TX indicator lights up, the ALC is showing some movement, but the wattmeter doesnt even twitch.

i already swapped the mic thinking it might be a silly thing like that. checked the PA fuse on the board, looks fine visually. im not great with RF troubleshooting at the PA stage but i do have a scope and a decent DMM. the bias on the finals is something i havent checked yet because honestly i wasnt sure where to start. anybody dealt with this specific symptom before on an 857 or similar yaesu rig? wondering if its the driver stage or if one of the finals just went quietly.

yeah that sounds like it could be the finals but dont rule out the driver yet. on the 857 the PA transistors are the Q1010 and Q1011 if i remember right, RD70HVF1 MOSFETs. what i'd do first is check the drain voltage on those with the rig in TX — should be somewhere around 13.8v obviously, but also check that gate bias is actually getting there. if the driver stage isnt putting out signal to the gates you'll get exactly what you're describing: ALC moves a little because the ALC circuit is seeing something upstream, but no actual RF makes it out.

the other thing i'd look at is the LPF relay board. those relays can get flaky and i've seen them cause complete loss of output while everything else looks normal. if you have a way to inject a small signal and probe after each stage that's really the cleanest way to isolate where it's dying. don't just shotgun replace the finals before you're sure, those parts arent cheap and if the driver is toast and you put new finals in without knowing, you can take the new ones out too.

had almost the exact same thing on my 897 a while back, different rig i know but similar architecture. turned out to be a cold solder joint on the driver board, totally invisible until i reflowed it. worth going over the board under good light with magnification if you havent already, especially around any connectors or anything that might have had mechanical stress. probably not your issue but took me two weeks of chasing more exotic faults before i found something that basic so figured id mention it.