so ive been sitting on doing this for like two years because i kept reading horror stories about people bricking their rigs but finally just went ahead and did the mars/cap mod on my FT-857D last weekend. honestly not as scary as i thought once you actually get in there. the jumper is right where everyone says it is and the hardest part was just not losing the tiny screw near the PA board.

anyway the point of this post is that while i had it apart i also replaced the stock electrolytic caps on the audio board because mine was already about 12 years old and the receive audio on 2m always sounded a little muddy to me. threw in some nichicon fine golds i had in the junk box and the difference is actually pretty noticeable, voices sound cleaner, less of that slightly boxy quality i could never quite figure out. could be placebo but i dont think so.

also looked at doing the rx sensitivity mod but chickened out on that one, the alignment is touchy and i dont have a good enough signal generator to do it right. anyone actually done that one and think its worth the trouble? my 857 RX is fine on HF but it always felt a little deaf on 2m compared to a dedicated VHF radio.

yeah the cap swap on those older Yaesu rigs is almost always worth doing if you're already in there for something else. i did the same thing on an 897D a while back, used Panasonic FR series and got similar results on the audio. the stock caps are not bad but after a decade they do drift a bit especially in the AF stages.

on the 2m sensitivity thing — honestly the 857 was never a stellar performer on VHF compared to a dedicated rig, thats just kind of a given with these all-band radios. the rx mod involves peaking L1003 i think it is, tiny coil near the VHF front end, and yeah you really do want at least a calibrated signal source to do it properly otherwise you're just guessing. i tried it once with a cheap SDR as a reference and got it slightly better but i wouldnt call it scientific. if you do a lot of weak signal VHF work it might be worth taking it to someone with an actual bench setup, otherwise probably not worth the risk for casual use.

the mars mod on that radio is pretty harmless yeah, i did mine years ago and nothing bad happened. though i'll be honest i barely even use the extended TX, mostly did it out of curiosity.

caps in the audio chain — interesting, i never thought about doing that. mine is about the same age and the audio has always been a bit meh on VHF but i just assumed thats how it sounded. might actually pull mine apart and have a look now that you mention it. what value caps were the ones you replaced, same value as stock or did you go up at all on the voltage rating?