so ive been chasing this one for about two weeks now and im at the point where im just going to post about it because i clearly cant figure it out on my own. the radio receives fine, i can hear everything perfectly, swr is where it should be, power output looks normal on my meter (about 95w on 40m which is what i expect). but apparently when i transmit nobody can hear me or they say its just a faint carrier with no audio at all.

ive already swapped the mic and that wasnt it. checked the mic connector for cold joints and reflowed a couple that looked questionable, still the same issue. the ALC is doing something when i key up so the PA stage isnt completely dead. im starting to wonder if its somewhere in the modulator section or maybe the mic amp itself. i did notice the mic gain pot feels a little scratchy when you turn it but even cranked all the way up no difference.

anyone dealt with this on an 857? or really any similar symptom on any rig. im running out of ideas and the service manual isnt exactly written for humans to understand.

scratchy pot is your first clue honestly. those carbon pots in the yaesu rigs get oxidized and it doesnt matter where you set them, the wiper just isnt making good contact. i had almost the exact same symptom on my 897 a few years back, everyone heard dead carrier, and it turned out the mic gain pot was intermittent enough to drop the audio to basically nothing even though it felt like it was passing *something*. hit it with deoxit, work it back and forth about 50 times, then see if anything changes. if the scratchy feeling goes away and audio comes back even partially then you know where to look. if that fixes it great if not at least you ruled it out cheap before digging deeper into the modulator board.

also worth checking — is the mic set to the right input on the menu? 857 has that setting for front vs rear mic input and ive seen people chase ghosts for days because of that one. probably not your issue but worth 30 seconds to confirm.

yeah deoxit on the pot for sure, thats the easy answer and probably right. but if that doesnt pan out id scope the mic amp output before assuming its the modulator. on the 857 the mic preamp is on a separate little board and those electrolytic caps on it can go leaky or just lose capacitance over time, especially on a rig thats been around for 15+ years. a leaky coupling cap before the modulator would give you exactly what your describing — carrier present, ALC reacting, but no actual audio getting through to be modulated. caps are cheap, if you find one thats drifted out of spec just replace the whole section while you're in there. not a hard job if you've got decent soldering skills and patience.