Canon EF 100-300mm USM Lens - Autofocus Issues

[mr.mike]

Just received a Canon EF 100-300mm lens autofocus out of commission. Manual focus working fine with one peculiar issue. You can turn the focus ring with the camera facing down and it's fine, but if you have it pointed up, the focus seems to slip. As soon as you point it down or straight ahead, it's working fine again. The EF 100-300mm lens has a rear focus ring. Wondering if anyone has an idea what the problem is? The autofocus problem may be in the switch or possibly a bad ribbon cable. I really don't care about autofocus on this lens, it will only be used on a limited basis. The slipping manual focus is annoying.

 

[zombiesniper]

Without having it hand it could be a focus clutch issue.

Is there any forward/backward play in the focus ring? If you put your ear to the lens and tip it up and down, can you hear anything move?

 

[mr.mike]

Without having it hand it could be a focus clutch issue.

Is there any forward/backward play in the focus ring? If you put your ear to the lens and tip it up and down, can you hear anything move?

Hi,
The focus ring doesn't have any play and there is no sound of anything loose when I tilt the lens in either direction. Manual focus works as it should when tilting down. It only slips when in the upward position. Thanks for your response.