so this has been bugging me for a couple weeks now. picked up an FT-857D off a local ham who said it worked fine and honestly i believed him because it does work fine... mostly. on 40m and 80m i get the full 100w out, checked it with my bird meter, no issues. 10m also seems okay maybe slightly low but within reason. but 20m is just sad, like im getting maybe 8-12 watts out depending on where in the band i am and the power output control doesnt really change much when i turn it.

no weird smells, no overheating that i can tell, SWR is fine because ive tried it into a dummy load. RX on 20m is totally normal. its not a filter issue i dont think because i swapped to a different antenna just to rule that out.

my first instinct is a driver transistor or one of the finals is starting to go on that band but im not sure enough to start poking around in there. has anyone seen this specific symptom on an 857? curious if theres a known weak point on these for 20m specifically or if i should just be looking at the PA board generally.

yeah the 857 PA board is a bit of a headache. the RD70HVF1 finals can degrade unevenly across bands, its not always a total failure, sometimes you just get one transistor that's limping along and it shows up worse on certain frequencies depending on how the bias network is reacting. 20m being the worst band for it is pretty common from what ive seen.

before you pull the board though id check the bias adjustment pots, theres a trimmer for the PA bias and if someone messed with it or if it drifted you can see weird band-specific power issues. the service manual has the procedure, you need a RF power meter and a dummy load and just work through it methodically. sometimes thats all it is and you save yourself from swapping transistors you dont need to swap. if the bias is set right and youre still low on 20m then yeah start looking at the transistors themselves, but i wouldnt skip that step first.

had almost the exact same thing happen on my 897 which shares a lot with the 857 design. mine turned out to be a cold solder joint on the PA board near one of the driver stages, was making intermittent contact and the symptom was low power that was worse on some bands than others. drove me nuts for a month before i found it just by reflowing a few suspect joints under magnification. worth a look before you go buying transistors.