so ive had this 857 for about 4 years now, picked it up used and it's been solid until maybe a month ago. noticed my signal reports on 40m were garbage compared to what i usually get and finally got around to putting a wattmeter on it. im seeing like 8-12 watts on 40m no matter where i set power, but 20m, 15m, 10m all look fine, hitting full 100w or close to it. 2m and 70cm also fine.

it's not the antenna situation, i swapped to a dummy load to confirm. the rig itself doesnt throw any error codes, SWR protection isnt kicking in, it just... quietly puts out almost nothing on that band. driver stage issue maybe? i've seen some stuff about the low band driver transistors on these going soft but im not sure how to actually verify that without just throwing parts at it.

anyone actually dug into one of these for a band-specific power issue? i'm decent with a soldering iron and have a scope but not super experienced with RF troubleshooting specifically. not sure if i should just send it to a tech or try to work through it myself.

had almost the exact same thing happen on a buddies 857 a couple years back, also 40m, also just quietly low power. turned out to be one of the driver transistors on the HF low band section — think it was a 2SC2078 or equivalent, dont remember exactly. the thing is they dont always fail hard, sometimes they just degrade and you get this kind of soft low output on certain bands because the drive to the finals is insufficient even though the finals themselves are fine.

if you've got a scope you can probe the driver output and compare what you're seeing to the schematic levels. the service manual for the 857D is floating around online, definitely grab that if you dont have it. the block diagram in there makes it a lot clearer which stages are band-switched vs shared. also worth checking all the band-switching relay contacts while you're in there — a dirty or slightly oxidized relay contact on that band could cause this too and that'd be an easier fix than transistors.

i wouldnt just throw parts at it before you scope it out a bit, but also these arent super exotic repairs if you're comfortable inside a rig. just be careful around the PA section, there's some caps that hold charge for a bit after power off.

the relay thing is worth checking first honestly. i had weird band-specific weirdness on an older icom and it was just a relay contact that needed cleaning. way less scary than digging into the driver stage. deoxit and a few cycles of keying it sometimes sorts it out, sometimes not, but its a 5 minute thing to try before anything else.