The customer has got a used Tamron 17-50 F2,8 lens, and realized that using with a Canon strobe, there is no change on the strobes display, it shows always 17mm focal length.
I was sure that there has to be something with the zoom position brush, so I disassembled the lens.
When moving the zoom ring, I could feel that the zoom tube does not follow too tight the ring. This happens, when the follower, a casted metal parts sits not strong enough on the ring, loosen screws.
But what I have found in the inside, was more over my expectation….
In the inside of the lens there was no zoom-brush – and no flex cable at all.
And as flex cables usually dont sublimate… The seller has forgotten to tell, that the lens is a repaired one, better to say, assembled without repair.
DIGITAL CANON repair blog 
I have this flex. I can send it to you. 🙂
Wow. Do you have the brush too? How much would You charge for that two parts with post to Hungary? You could answer in a mail: ruzsa . janos @ canonrepair . hu
Ive encuntered same problem and solved itn over ebay, for under 20 EUR these flexes are pretty easy to find… however my lens didnt even had the brush at all 😀
Shame for me that little bastard was not working even after my fix so its been sold to next DIYer
Probably the initial fault was encoder brush and encoder flex damaged. He just removed these damaged parts in order to zoom the lens. Bad job there
It is so sad that the poor buyers are so unprotected against such used lenses and cameras. And i am sure, that the focusing is also affected.
Most likely, that’s standard problem on that lens. When that casted part that connect zoom ring to the barrel gets loose, bottom of the screw that hold wiper start to scratch the flex encoder. I have repaired few of those (installed new wiper and flex cable).
Btw. lens works ok without that encoder. No problem with focus, just no report to camera about focal length (with obvious consequences).
Great repair by the previous assembler 😀
Another great thing that you cannot trust in the faulty things at all; i just bought not the first camera (1000D now) with “does not turn on” error description and horrible water damages :S