Opticallimits

Hi

I bought a secondhand Canon EOS 3 which the previous owner said was in perfect working order. Everything seemed fine but half way through the first roll the shutter seemed to jam. After a while it worked again, but then the autofocus seemed not to work properly, and the viewfinder seemed dim. It couldn't find focus or got the wrong focus. After a while I rewound the roll and fired the shutter a lot and this seemed to cure it. 

Does anyone know what is likely to have caused this and if it will happen again? Thanks 

Hmmh, dark viewfinder smells like something with the depth-of-field preview or aperture control - both would dim the viewfinder.
As far as the jamming is concerned - the camera has probably barely seen any use in recent years. That may have had some side effects on the motors.

I guess you mean the shutter button stuck? Now that it works again, you know it can get stuck on the down position, I guess. The dim view finder and AF issue sounds like the lens' aperture did not open up, got stuck. That then is a lens issue, not a camera issue.

Does this happen with all lenses or just one lens ?? Seems mostly like a lens issue to me with aperture or flex cable problem

Have you tried using a new battery?

I have an EOS-5 analog camera, and that did this when the battery was very low.

HTH, kind regards, Wim