This sounds like the infamous Command Dial problem of the A2/EOS5, which can happen if the user forgets to press the release button when moving the Command Dial away from the lock position, resulting in some shearing inside. I've not encountered it on my EOS 5, though I'm very careful about it and have a small sticker on my camera to remind me to take care when changing modes across the 'lock' position, though in truth I generally only use Av or M.
Originally Posted by Chriscc123
A net search for 'Canon A2 (or EOS 5) command dial problem' will bring up lots of instances describing it. Some have fixed it themselves, though I don't think my tinkering skills are up to the job.