so ive been sitting on doing the mars/cap mod on my FT-857D for probably two years now, just never got around to it. finally pulled the trigger last weekend and honestly it went smoother than i expected. basically just moving a couple diodes on the main board, took maybe 20 minutes once i had the radio open and could see what i was doing.

what prompted it was i wanted to be able to monitor some freqs just outside the normal ham allocation and also mess around with NVIS stuff for our local emcomm group where we sometimes need a little flexibility. not gonna lie the service manual on that radio is actually pretty decent once you find the right revision, some of the older ones floating around dont have the right board layout diagrams.

while i had it open i also reseated the finals heatsink because ive read a few places that the thermal compound from the factory isnt great and mine was definitely dried out and crumbly. put some decent MX-4 on there. hard to say if it made a measurable difference in output but it certainly cant hurt and the radio runs a little cooler i think on long digital mode sessions.

anyone else done mods to theirs? curious if theres anything else worth doing to this radio while i have the confidence and tools out. i know people talk about the fan mod for continuous duty stuff but im not sure if i need it for my use case.

yeah the thermal compound thing is real, did the same thing on mine about a year ago. the stock stuff on those yaesu radios from that era is pretty mediocre. i used arctic silver which is probably overkill but whatever i had on hand.

the fan mod is worth doing if you run any digital modes for more than like 10-15 minutes at a stretch, the stock fan curve is pretty conservative and the radio will throttle before it should on a warm day. its not a hard mod, just a resistor change if i remember right, or some people wire in an external fan controller. i did the resistor version and it made the fan kick on a bit earlier and run faster. radio is a little louder now but runs noticeably cooler on JS8Call sessions.

one thing i will say, double check your output power on all bands after you do any board work. mine was slightly off on 10m after i had it open once, turned out i bumped a trimmer pot. nothing a quick tweak couldnt fix but if i hadnt checked i wouldnt have known.

the 857 is a solid rig for modding, good choice. i did mine years ago and also added the CAT interface wiring at the same time since i had it open anyway, saved having to go back in later. if you havent set up CAT control with it yet its worth doing, makes it way more useful for logging and digital mode software.