so this has been sitting on my bench for about two weeks now and im starting to lose my mind a little. picked up an ft-857d at a hamfest for cheap because the guy said it had 'some tx issues', which i figured meant maybe a bad connection or something simple. not so simple.

the radio receives fine, actually pretty decent on most bands. when i key up it shows like 2-3 watts on the internal meter on 40m and basically nothing on 20 and up. the finals look okay visually, no burn marks, no smell. already resoldered the PA board connections because one looked a little cold. checked the voltage rails and theyre within spec, 13.8v at the main connector. ALC looks like its doing something but maybe clamping too hard? honestly not sure.

i pulled the driver board and inspected it under magnification, nothing jumped out at me. checked Q1035 which is a common failure point on these from what ive read and it measured fine out of circuit. im kind of wondering if one of the LPF relays is flaky, i can hear them clicking when i change bands but that doesnt mean theyre actually switching cleanly i guess.

anyone gone down this road on an 857? before i start throwing parts at it i want to make sure im not missing something dumb.

yeah the LPF relays on those are absolutely worth suspecting, ive seen that exact symptom on an 897 which is basically the same guts. the relay contacts can look fine but have high resistance that only shows up under RF load. what i did was unsolder each relay and measure contact resistance with a decent meter, anything over like half an ohm and youre probably in trouble. also worth cold spraying the relay bodies while keyed up and watching the power meter, sometimes thermal helps you nail down which one is the problem child.

the ALC thing you mentioned is interesting too though. if somethings pulling the ALC line down it can absolutely kill your output without any obvious cause. do you have a scope? poking around the ALC feedback loop while transmitting into a dummy load has saved me a lot of time on yaesu stuff.

had almost the exact same thing on mine a while back, turned out to be one of the driver transistors was leaky. not fully dead, just leaky enough to mess up the bias on the whole chain. it measured okay static but when i did a dynamic test it was clearly unhappy. cant remember the part number off the top of my head but its in the service manual, which if you dont have yet you really need to grab it because the alignment proceedure in there is actually pretty good for diagnosing where the chain breaks down.