so ive been sitting on doing the mars/cap mod on my 857D for like two years now and finally got around to it last weekend. not gonna go into the full procedure here since its all over eham and the yaesu groups but just wanted to share some observations after running it for a few days.

first off the actual mod itself took maybe 20 minutes, just the one diode removal like everyone says. no drama there. but what i actually wanted to talk about is the difference it made running it into my external LPF bank when doing some 60m stuff. seemed like the finals were running a bit warmer than before on extended transmissions which i half expected, but nothing scary on the meter.

the thing im actually more curious about is whether anyone has done the fan mod on these at the same time. ive seen a couple writeups where people swap out the stock fan for something with better airflow since these things run warm to begin with. my understanding is the stock fan is pretty mediocre and there are drop in replacements that move a lot more air. anyone done this and was it worth the hassle of pulling the whole top cover off again

yeah did both on mine about 3 years ago. the fan swap is honestly more impactful than the tx mod in terms of day to day usability. i used a noctua 40mm, had to do a tiny bit of trimming on the mounting tab but nothing serious. temps dropped noticeably during long digital sessions, i run wspr and js8call a lot so the duty cycle was really cooking the stock fan. the tx mod on mine has been fine, run it into a separate lowpass for anything outside the ham bands and havent had any issues. just dont be dumb about it and run it barefoot into a random wire or something and you should be ok.

i did the fan mod but skipped the mars thing, didnt really have a use case for out of band tx. the fan writeup i followed was by someone on qrz forums i think, they measured temps before and after with a thermal probe and it was like 15 degrees C difference under load which is pretty significant for a rig thats already in a marginal thermal envelope. one thing to watch on the 857 is the connector on the fan wires is kinda fragile when you unplug it, go slow or you'll be buying a new JST connector from digikey and cursing for an afternoon. ask me how i know lol