so ive been sitting on this for a while but last weekend i finally pulled the trigger and did the mars/cap mod on my FT-857D. not a big deal electrically, its literally just moving one diode, but i was nervous about it for way longer than i should have been. the whole thing took maybe 20 minutes including the time i spent second-guessing myself with a magnifying glass.

anyway the reason i bring it up is because while i had the covers off i also went ahead and did the ref oscillator mod that ive seen floating around on eham and a few other places. basically you replace the stock TCXO with a better one and the frequency stability on 2m and above gets noticeably tighter, especially before the rig warms up. i was getting maybe 200-300hz of drift in the first few minutes on 2m and now its pretty much rock solid from cold start. that actually matters to me because i run some weak signal stuff and it was annoying.

the other thing i did was replace the stock electrolytic caps on the AF board while i was in there. a couple of them measured a little low on capacitance and at this point the radio is old enough that preventive stuff like that makes sense. audio sounds cleaner to me now but that could just be placebo, hard to say.

if anybody else has done mods on these rigs id be curious what else is worth doing. ive seen stuff about the AGC mod but havent dug into it much yet.

the AGC mod is worth it imo, at least if you do any SSB on crowded bands. the stock AGC on the 857 is a bit aggressive and you get that pumping effect when there's a strong signal nearby. the mod basically changes a couple resistors to slow the attack a little, i think R1159 and R1162 but dont quote me on that, check the actual mod writeup because i cant remember the exact values i used. made a noticeable difference on 20m during a contest weekend.

also since youre already going in there — if you havent already swapped the fan for a quieter one thats another easy one. the stock fan is loud and the replacement is maybe a 5 dollar part. some people add a small resistor to drop the voltage slightly so it runs slower at idle. i did that and the noise floor in my shack dropped enough that i actually noticed it on voice operation.

nice write up. did you have to recalibrate anything after swapping the oscillator or did it just drop in and work? i ask because ive got an older 897D sitting here with similar drift issues and been wondering if the same mod applies, the architecture is close enough that it might but im not 100 percent sure the part number crosses over cleanly.