I know a common fault of the T610 and other Bauer Studio Line machines is often, after many years of standing idle, an issue regarding the threading mechanism.
I have had to do some work myself in the past regarding these issues and because of this, I would like to post something of a technical write up surrounding these issues.
The freedom of the linkages on the Bauer series of projectors and many others it has to be said,is of uppermost importance to enable a good,healthy and reliable threading mechanism.
Here i hope to highlight and show via a set of photographs the work that is needed to be able to correctly "free up" any mechanism that is proving to be troublesome after many years of lack of use.
I will begin by showing the correct position of the top roller and curved feed guide when all is as it should be. The curved plastic feed guide into the gate should move consistently down into position in order to make the film enter the steel rear gate guide without causing any hesitation or bunching.
This first photograph here shows the position the curved plastic feed guide should be in for the film to be able to load on autothread position which is the first position of the main control knob in the forward direction.
This next photograph shows the position the top roller and curved feed guide should be in when the film has correctly threaded onto the take up reel and the main control knob is moved into position 2 or 3 (half or full lamp power, forward projection mode)
note how the curved guide should now, reliably and consistently, move completely away from the running film leaving the film itself to stay within the original shaped loop created by the curved guides initial threading position.
Now we move onto the lower "assist" guide and roller.
Again in the initial threading position, as selected by the main control knob, this is how it should appear if all is healthy and working A1.
note on close up inspection on this photograph how the roller sits right up against the assist lower plastic guide to enable the film to forced into the tiny slot for the magnetic head section, both accurately and completely reliably.
Now we move onto how the lower roller and assist guide appear in the run position (position 2 or 3 in the forward direction on the main control knob, main projection lamp lit on half or full power).
note now how the "assist" guide and roller again move completely out of contact with the film. Once again, once the film has entered the magnetic head section, it will have formed a lower loop of it's own from where the roller and guide forced the film to enter into the magnetic head section.
For all this mechanism to work correctly and reliably as seen in the photographs above, it relies entirely on a series of linkages and springs to all be present and all be free to move exactly as they were designed to do so.
The majority of this linkage arrangement can be seen here in this drawing taken from the 502/525/610 service manual.
please study the drawing to gain a general understanding of how the linkages are arranged and assembled in the factory.
In particular, please take note of item 1160. It is a pivot point within the mechanism that if you will pardon the pun, is absolutely pivotal to the rest of mechanism working reliably and accurately each and every time. It is this part in particular that can often be very stiff in it's movements and can therefore cause many issues surrounding the threading action at both the top and lower loops.