Khang1611

This is where the cable being folded roughly ( sorry I forgot to take pictures when I reassemble it). I recommend using some alcohol for disassemble cause they have glue at some parts. And that’s it, I think that’s thee problem cause we concentrate on the ic chip too much, my dad said that those parts on the main board are rarely break. And this cable are the electric parts that being move the most and in a roughly way. 
i hope my comment will help u guys to fix this lens. 

Hey guys, after five days of me and my dad tried to fix the xf 27mm f2.8 i think we figured it out the problem caused the error. Let’s directly into it. Also i’m not a native English so I will try my best to explain my idea. I think that the problem could be the aperture cable, as its being taped down roughly on the plastic piece, when the lens. Moving in and out, it’s being folded like a hinge. After like 4-5 years of using the cable inside probably got weaker and caused the error. Or even like my situation( got broken). So what i did is that i ordered another cable from china ( Aliexpress have it, just type in xf 27mm f2.8 parts ) then I transferred all the small parts like the censor, the aperture motor, the small chip ( resistor I guess ) to the new cable and put everything back in. But at the plastic piece instead of do it like Fujifilm, I used a piece of tape to wrapped around it like a collar to give it more angle of movement. Mine is work perfectly now after the fix. ( I bought it broken from another person )