so ive been sitting on doing this for like two years now because i was always nervous about voiding the warranty (which is already long gone lol) and also just the general fear of bricking a radio i rely on for portable ops. but i finally sat down last weekend and did the mars/cap mod plus the extended receive on my FT-857D and honestly it went smoother than i expected.

the mod itself is pretty straightforward once you find the right diode matrix — theres a lot of conflicting info online about which pads to bridge depending on the firmware version so just make sure youre looking at the right diagram for your specific unit. mine is an older one so the pad layout matched the older docs. took maybe 20 minutes total including pulling the bottom cover off.

extended rx is working great now, been listening around on some frequencies i couldnt touch before. the transmit unlock i honestly probably wont use but it was part of the same mod so whatever. what i actually want to do next is look into improving the audio on rx, the stock filtering always felt a little mushy to me especially on crowded ssb. anyone done anything with the IF filtering on these? i know you can drop in a Collins mechanical filter but im not sure if thats actually worth the cost vs just using DSP filtering in the radio or an external audio filter downstream.

yeah the diode matrix stuff on those older Yaesu portables always has like three different versions floating around the internet and half of them are wrong or for a different production run. glad you found the right one without letting the magic smoke out.

on the IF filter question — i did the collins filter swap on mine probably four or five years ago and honestly it does make a noticeable difference on a really busy band, especially 40m ssb when everybodys piled up. but its not a night and day thing. if youre already using the DNR and the width/shift controls effectively you might not feel like its worth the $60-80 for the filter depending where you source it. the bigger improvement i noticed was actually when i started using an outboard audio filter, i had an old MFJ-784B sitting around and running that off the speaker output cleaned things up quite a bit for ragchewing. probably a cheaper experiment to try first before you go digging back into the chassis.

also one thing — after you did the rx mod did you notice any change in sensitivity on the standard ham bands? i always wondered if bridging those pads messes with anything on the normal receive path or if its purely additive.

i did basically this same mod like six months ago and the only thing i'd add is double check your ground points before you button it back up, i had a weird intermittent crackle on vhf for a week before i realized i hadnt fully reseated one of the ribbon connectors. nothing to do with the mod itself just me being sloppy reassembling it.