I recently bought a used Canon 70-200mm F2.8 IS . The lens is in good condition, but it has an issue with auto focus. When you try to focus, you can see the focus ring spinning very fast, but it’s failed to focus , it seems only focus for object over 10mm or it’s at infinity.
After some research, it turn out that the issues was caused by a dirty focus sensor and focus bar. Below are the 2 videos that will help you to fix that problem. I did it it’s half success – the focus is now working, but i damage a flex cable causing the Image Stabilizer not working. Here are my notes for you.
Watch the 2 videos below several times before doing it – no hurry – the first one is for Non IS version, but this man show you very detail. The 2nd one is the extact version , but it’s not as detailed as the first one.
When you remove the protect cloth , take the photos how the cable running , my mistake was at this step and my ribbon was cut because i didn’t run the cable properly when i reinstall.
When you are working with the USM motor, try to put it upward because there is small ball that can easily falling out. The first video mention where it is, you better look at the ball first so if it’s falling out, you know where to put it on.
When you re-assembly, the USM or IS module has a lever, this lever connect to a small the the bottom part, if these levels are not in correct place, you will see the result that your zoom is stuck at 135m – The first video shows it very detail.
Before connecting the ribbon cable back, check the focus ring and zoom ring , they should move smoothly, if it’s stuck or hard to spin, check the lever.
Carefully connect the ribbon cable back – attach the protect cloth tape back tidy so we can put the barrel back easily.
Good luck.