so ive been sitting on doing the mars/cap mod on my FT-857D for probably two years now, kept putting it off because i was paranoid about voiding warranty on a radio i actually use daily. finally just did it last weekend and honestly wish i had done it sooner.

the mod itself is pretty straightforward, theres a diode on the main board — D3001 i think from memory — that you either cut or remove depending on which version of the mod you want, and it opens up extended TX. takes maybe 20 minutes if you're not rushing. i did have to remove the bottom plate and the display assembly which was a little nerve wracking but nothing broke.

what i actually wanted to talk about though is whether anyone has also done the internal cooling fan mod at the same time. mine runs warm during extended digital mode sessions and ive seen a few threads elsewhere about swapping the stock fan for something quieter and higher CFM. thinking about one of those noctua fans but not sure if the voltage regulation on that circuit is stable enough to not cause issues. anybody gone down that road with the 857D specifically? the 897 mods dont always translate directly and id rather not fry the PA section finding out.

yeah the diode mod is dead simple, did mine years ago. on the fan thing though — i went a different route and just added an external heatsink to the bottom plate with some thermal adhesive pads on the finals. not as elegant as a fan swap but its been rock solid through two summers of JS8Call and Winlink sessions. the stock fan on these radios really wasnt designed with digital modes in mind, yaesu was thinking mostly voice and CW when they spec'd the thermal management.

the noctua idea isnt crazy but you'd want to check what voltage the fan header is actually putting out under load. i measured mine at like 7.8v which is a bit low for most PC fans to run reliably at. some guys use a small voltage regulator inline but at that point its more work than its worth unless you're really committed to keeping it all internal.

dont overlook just cleaning the existing fan and making sure the vents arent clogged, mine was running way hotter than it should have been and turned out there was like 3 years of dust basically insulating the heatsink. embarassing fix but it worked lol