Pentax 645 "Single Shot" Mode Problem

<p>Recently got a P645 (original) and 75mm lens cheap ($30) due to AA batteries leaking in the grip and the owner wasn't able to demo the functioning of the camera.<br>

Anyhow I got the battery corrosion pretty well cleaned up enough to power up the camera and it seems to operate for the most part. One other issue it had was the geared film roller that operates the frame counter gear was bound from an end of it becoming unscrewed and jamming its rotation. Since it didn't rotate, this caused the film to run to the end since it didn't think it ever got to frame 1. The lithium cell in the bottom reads about 3.0v and the memory is retained when the battery grip AA holder is removed.</p>

<p>I've got a old dummy roll of 1981 Tri-X I'm using to test with and if I, set the camera on "Single Shot" mode I can get one shot out of it, but as long as the power switch is on it will not take another shot. Turn the power off and back on I can get another shot. In "Continuous Shot" mode I can take a shot and fire subsequent shots with no problem. The frame counter does appear to be working correctly and at the end of 16 frames the camera won't fire any more, so the film insert contacts seem to be functioning correctly to indicate film end and block camera operation. I suppose I could just leave the camera in "Continuous Shot" mode and forget "Single Shot", but just the fact that it appears not to be right bugs me, so if I can do an easy fix I'll feel better.</p>

<p>I did find mention of a similar problem someone had in another forum and stated a camera tech thought it was likely to be the frame counter gear at an estimated of cost of $150. The poster of that thread opted to sell the camera , so I don't know if the "frame counter gear" assumption was ever correct. Where the camera I have appears to count correctly I'm less inclined to think there is a problem with that gear.</p>

<p>Open to any ideas or just tell me that switching the power switch off and back to on is normal and acts like a manual film advance crank :)</p>