How to Troubleshoot Minivator Residential Elevator ?

I have a Minivator (Thyssen Kruppe) that when going up from lowered position will ascend a few inches then reverse and descend a few inches. It will do this multiple times before finally continuing all the way up...I suspect its something like the reel tensioner safety but no idea how to track the problem down. Called the mfg and their service is $425 / hour + parts...