I have had this happen on other cameras, but none of my Canonets. The mechanism is a galvenometer, a needle on an electromagnet. They are very sensitive. I have a Nikon that requires a "rap" on the head to work, but after that it is fine for the day. Usually it is a bent needle or something bent in its path. Rarely, the mechanism itself is bad. On the Canon 7, opening the camera up was required. A light baffle had become bent, and I ended up removing it. On that camera there was no margin for error. On another camera, it was easy to bend the needle slightly.
I think that "Greyhoundman" has been through this before, and has some pictures of the effected area. If it is as simple as a bent meter needle hanging up on its track, it means popping the top plate. That is not difficult, I use a rubber mousepad to get the cover over the wind-lever off adn jewler screwdrivers for the screws.
