Canon 17-85mm IS USM repair

[Coop]

I recently bought a kippered example of the above lens with the intention of fixing it

I was lead to believe the 'normal' fault with these is an error 01/99 that's caused by the APERTURE flex cable flexing over the years and cracking.

however the lens I have has a focus issue that see's it hunt for focus at the upper ends of the zoom range (above 40 odd mm) and be totally hit and miss as to if it does eventually focus. sometimes it beeps focus and flashes in the viewfinder when its so far out of focus its laughable

as such I am now unsure as to if replacing the aperture cable is going to go anywhere to fixing this focus issue or are the two intertwined? either way its definitely not causing a visible/flagged error on the camera, it just wont focus correctly in AF mode

could it be dirty contacts elsewhere, I have read about the photocoupler or something that's part of the USM motor? could be the issue?

anyone actually got real first hand experience of this fault (not the error 99 one) and managed to fix it?

cheers

Ben

 

[Coop]

well, ripped the lens apart today and cleaned the photoelectric sensor thingie inside the USM motor mechanism, but it wasn't really that dirty

re-assembled and no different!

as such I've now ordered a replacement aperture ribbon from ebay and I will slap that in when it arrives and see if I can resolve the issues.

 

[Coop]

on a side note its easy to see how dust etc gets into some of these lens'

this particular canon example isn't exactly well sealed, its just slotted together with some fairly useless looking felt bushes between the zoom rings and the front element is just covered by the little sticker with the manufacturers/lens info stamped on it.