so ive been sitting on doing the mars/cap mod on my FT-857D for probably two years now and finally just did it last weekend. pretty straightforward honestly, just the one diode removal and you open up the TX range. i know some guys arent into this kind of thing but i wanted to be able to test some stuff on NVIS freqs for our ARES group without having to borrow someone elses rig every time.

anyway while i had the covers off i also cleaned the fan and noticed the thermal paste on the finals looked pretty dry and crusty, so i went ahead and redid that too. pretty sure the radio runs cooler now but honestly hard to say for sure without actual measurements. the fan does seem to kick on less during long transmissions though.

has anyone else done anything more involved on the 857D? ive seen some posts about a mod for the display backlight but im not sure if its worth the hassle. also wondering if the CAT interface performance changes at all after these kinds of mods, mine seems fine but one of the guys in my club swears his got flaky after he did something similar on his 897

did the same mod on mine probably four years ago, no issues at all. the thermal paste thing is good thinking — those finals are already working pretty hard in that little chassis especially if youre doing any kind of mobile use. i used Arctic Silver when i redid mine and it made a noticeable difference on the thermal cycling.

the CAT interface thing is almost certainly unrelated to the mod, more likely a ground loop or a bad USB adapter. the cheap FTDI clones have a habit of getting flaky over time. i went through two of them before i just bought the genuine Yaesu cable and that sorted it. might be worth telling your buddy to try a known good cable before he blames the mod.

the backlight mod is kinda meh in my opinion, i did it on mine and yeah its brighter but it also draws more current and i do a lot of portable ops so i ended up reverting it. depends on your use case i guess. if youre mostly home station then sure why not.