so i finally bit the bullet and replaced the PA transistors on my 857 after it started dropping to like 8 watts on 20m. got a pair of RD70HVF1s from a supplier and followed the usual process, matched them as close as i could on my curve tracer, thermal grease, torqued down properly.

now it puts out full power again on HF which is great but 2m is completely dead. like zero output, not even a watt. the driver chain seems fine because i can hear the ALC doing something when i key up on VHF, and the pre-driver stage is getting warm like it should be, but nothing making it out to the antenna port. checked the TX/RX relay and it seems to be switching correctly.

my gut says maybe i knocked something loose around the band switching logic or maybe the VHF PA module itself was already marginal and me poking around in there finished it off. its a separate module so i dont think the final swap should have affected it but stranger things have happened.

anybody dealt with a dead VHF section on one of these while the HF side is fine? wondering if its worth pulling the VHF module entirely and scoping the input to see if drive is even getting there before i start assuming the module is cooked.

yeah that VHF module on the 857 is basically its own little world in there, should be totally isolated from what you did with the HF finals. but i'd definitely scope the drive signal going into it first before you assume the module is bad. there's a little coax jumper that connects the VHF driver board to that module and i've seen those get dislodged or even cracked at the connector when people are working nearby. easy to miss visually.

also worth checking is whether you bumped the VHF ALC line during the job. theres a multi-pin connector somewhere in that area and if one of the ALC pins is floating youll get exactly what you're describing — the radio thinks its outputting but nothing actually comes out. the service manual has the test points laid out pretty well, page 63 or somewhere around there if i remember right. dont just assume the module is dead until you confirm drive is actually reaching it.

i had something similar on mine but it turned out to be that little relay on the VHF TX path, not the module itself. can't remember the part number off the top of my head but if you pull up the schematic it's pretty obvious. mine was switching but not making solid contact — looked fine on a DMM but under RF load it was basically open. swapped it and VHF came right back. probably unrelated to your finals work but worth ruling out before you go pulling the whole module.