so ive been putting this off for like two years but finally cracked open the 857D last weekend to do the extended TX mod. you know the one, mars/cap mod, just pulling the diode on the main board. straightforward enough if youve done any rig surgery before but there were a couple things that caught me off guard that i figured id post about since the writeups i found online were a little vague on certain steps.

first thing is the board in mine (i have a later production unit, not sure exactly when it was made but the serial puts it somewhere around 2011 or so) had the diode in a slightly different spot than the photos i was working from. not drastically different but enough that i was poking around in there longer than i should have been. if you have a later unit double check before you go snipping anything.

second thing, and this is the one that almost got me, the ribbon cable on the front panel is way more fragile than it looks. i disconnected it fine going in but clipping it back i felt it snag just slightly and spent a good 20 minutes convincing myself i hadnt damaged it. ended up being fine but just go slow on that part. everything powers up and works normally now, no issues on the ham bands and the wider TX is doing what its supposed to do. just sharing in case anybody else is about to go down this road.

yeah the ribbon cable thing is no joke, i nicked one on an 817 a few years back and it was a bad time. had intermittent audio issues for weeks before i figured out that was the culprit. ended up having to order a replacement from a parts supplier in Japan which took forever. good reminder to just be patient with those connectors, they are not made to be reconnected fifty times.

on the diode placement thing, i think Yaesu made a running change somewhere in the production run but nobody really documented it cleanly. ive seen a couple threads on eham where people were confused by the same thing. once you find it its obvious but finding it is the annoying part. glad it worked out, the 857D is a solid rig to have opened up TX on, pretty useful for the go-kit stuff.

been thinking about doing the same thing, mostly cause i do some MARS work and it'd be handy. my only hesitation is i really dont want to void anything or mess up the receive performance. does the mod affect RX at all or is it purely on the TX side? i know its just a diode but im always a little paranoid about unintended consequences when i start messing with stuff i didnt design