so ive been putting this off for like two years because i was worried about voiding the warranty but the warranty expired ages ago so i finally just did the MARS/CAP mod on my FT-857D last weekend. for anyone who doesnt know what im talking about it basically involves removing a diode on the main board that restricts the TX range, lets you transmit outside the normal ham bands which is useful if youre actually enrolled in MARS or CAP or whatever.

anyway the mod itself wasnt that bad, tiny soldering work but nothing crazy if youve done board-level stuff before. i used a magnifying headset and a fine tip iron, took maybe 20 minutes including the time i spent second-guessing myself. the rig came back up fine, all my normal ham freqs work exactly the same, havent noticed any difference in performance on 40m or 20m which is mostly what i use.

what i did NOT expect was how much better the RX feels on some of the lower freqs, like 160m and the AM broadcast band. not sure if thats placebo or if the mod somehow affected something but it does seem a bit more lively down there. probably imagining it. has anyone else done this and noticed anything weird after, good or bad? also thinking about doing the TX power mod next but ive heard mixed things about longetivity so might skip it.

did the same mod on mine probably three years ago, no issues at all. i wouldnt worry about the RX thing, i think thats just you paying more attention to the radio after doing work on it. that said i did notice after i did a separate IF filter swap that 40m really opened up for me, the stock filters on the 857 are just okay, not great. if you havent looked into adding a 500hz or 300hz CW filter in there its worth it especially if you do any contesting or just crowded band operating. bit more involved than the MARS mod but still doable at home.

the TX power mod — yeah i'd skip it honestly. heard of guys burning out the finals pushing those rigs harder than they were designed for and the 857 isnt exactly cheap to repair. the stock 100w is plenty for what most people need anyway.

the rx improvement is probably real actually, some of those region-restriction mods involve components that slightly affect front end loading on adjacent freqs, not always in a bad way. depends on exactly what Yaesu was doing with that diode in circuit. i wouldnt call it a major upgrade but its not always pure placebo either.

im more curious about the longevity question you raised. ive got an 857 thats been running the MARS mod for going on 5 years, uses it for emcomm activations mostly, no problems to report. but i run it pretty conservatively, rarely pushing it hard for long periods. if someones doing like contest operating at high duty cycle for extended periods thats a different story regardless of mods.