HP85s have 2 ways of chewing tapes, both fixable (normally). If the optical EOT sensor fails, then it'll run the tape off the spool. Often just cleaning the sensor will fix it. If not, then the electronics is not that complicated IIRC. The other (and more common) way is for the drive roller to run to glue. I have heard that silicone rubber tubing of the right diamter will fix this. As I've got some other HP machines where this has happened (9825, 9831, etc) I am going to have to investigate the exact methods of repair.