so ive been putting this off for like two years but finally cracked open the 857D last weekend to do the TX expand mod. for anyone who hasnt done it, its just a couple jumpers on the main board, takes maybe 20 minutes if you dont fumble around like i did finding the right pads. the service manual marks them pretty clearly once you actually look at the right page.

anyway the point isnt really the mod itself, its that while i had the thing open i noticed the stock cooling situation is kind of a joke. the fan is tiny and it basically only kicks on at full duty when the rig is already warm. ive seen people add a secondary fan or at least swap to a higher CFM unit, thinking about doing that next since i run it mobile and in the summer the PA can get pretty toasty on long ragchews on 10m.

anyone done the fan swap on one of these? or any other mods worth doing while its already open? i saw something about a receive preamp mod a while back but cant find the thread now.

yeah the cooling on the 857 is pretty marginal for sustained TX. i did a fan upgrade on mine about three years ago, just sourced a 12v fan with a higher flow rate and wired it to run at lower voltage most of the time with a small resistor in line so it doesnt sound like a jet engine at idle, then direct 12v when the temp gets up there. pretty simple mod honestly and the thermal behavior is noticeably better. i also added a small heatsink to the PA module itself, theres just barely enough clearance if you keep it thin.

the preamp mod you're thinking of might be the one where you piggyback a MAR or similar MMIC on the front end, ive seen it done but never tried it myself. my stock RX on the 857 has always seemed fine for what i do so never felt the urge.

dont forget to check if your particular unit has the MARS/CAP mod already done from a previous owner, some of the used ones floating around have it and some dont and its not always obvious unless you actually test outside the ham bands. found that out the hard way when i bought mine secondhand and assumed it was stock.