so i've had this 857D for probably 6 years now and always ran it stock because i was worried about screwing something up but last month i finally just did the extended TX mod and honestly it was way less scary than i built it up to be in my head. just a couple diodes on the main board, took maybe 20 minutes if you count the time i spent staring at the service manual convincing myself i had the right pads.

while i had it apart i also went ahead and did the filter mod for the IF, swapped in a 500hz CW filter that i had sitting in a box forever. big difference on crowded bands, should have done that ages ago. the radio feels like a different rig now on 40m when things get busy.

anyway i guess my question is — has anyone done the fan mod on these? mine runs pretty hot on digital modes and i've read about people replacing the fan with a quieter higher CFM unit but i cant find a consistent answer on whether the stock thermistor circuit handles a different fan okay or if you need to mess with that too. dont want to cook the finals just to get a quieter fan noise.

yeah the fan swap is pretty straightforward on the 857, the thermistor just controls voltage to the fan so as long as your replacement fan operates in the same voltage range you're fine. i used a Noctua 40mm on mine, had to do a connector swap but the thermal response was basically the same. just dont go with something that needs 12v minimum to start spinning or it'll sit there not moving at low temps and then kick on hard when it finally gets hot enough, which kind of defeats the purpose.

also good call on the IF filter, i keep meaning to do that on mine. which filter did you end up going with, the Inrad or one of the murata options?

I did something similar on my 897D a while back and while I was in there noticed one of the trimmer caps looked a little sketchy, ended up doing a full alignment after the mods which probably helped as much as anything. not saying yours needs it but if you have a frequency counter and some patience its worth checking after you've had the board out. these older Yaesu rigs can drift a bit over the years and people attribute it to the mod when really its just age.