so ive been sitting on this for a while but last weekend i finally cracked open the 857D and did the mars/cap mod to open up the TX range. pretty straightforward once you find the right diodes, took maybe 20 minutes total including finding my reading glasses. the service manual PDF floating around online has the right diagram if you search for it.

anyway the reason i did this wasn't really for transmitting out of band, more because i wanted to use it on some of the EMCOMM frequencies that sit just outside the normal ham allocations and needed the flexibility for testing purposes. the radio came back up fine and TX looks clean on the dummy load. SWR is behaving normally.

while i had it open i also reflowed a couple solder joints near the PA section that looked a little cold — not sure if that was from factory or just age, the radio is maybe 8 years old at this point. hard to say if it made any difference but it felt like the right thing to do while i was already in there.

anyone else done any other useful mods on this radio? ive seen some stuff about the cooling fan mod and im curious if its actually worth doing or if thats more of a worry-about-nothing thing. mine gets warm on digital but hasnt caused me any real problems yet

the fan mod is worth it if you run any kind of digital modes for extended periods, honestly. i did mine after the finals got flaky during a long JS8Call session — couldn't prove it was heat related but after swapping in a better fan that kicks in earlier it's been solid. the stock fan threshold is set pretty conservatively high and by the time it actually spins up the PA has already been cooking for a while.

what i did was just replace the fan with a higher CFM unit, same voltage, and added a small inline resistor to drop the speed a bit at idle so it's not screaming the whole time. there's a thread on eham somewhere from years back with the exact resistor value but i dont remember off the top of my head, probably worth digging up before you just slap anything in there. the 857 is a great little radio but yaesu really did cut some corners on the thermal management given how much they stuffed into that chassis.

yeah i did the same mod on mine a couple years back, no issues. one thing i'll mention is double-check your TX audio after you do it, some people report a slight difference in how the ALC behaves when operating near the edges of the extended range. might be nothing, might matter depending on what you're doing. i ran mine into an external wattmeter and everything looked fine but worth verifying with something other than just the built-in meter.