I have a Sony MDS-JE640 (and a couple of 530s that get pressed into service if a lot of discs arrive)
Steve, I also have a large unit similar to these. Recently it stopped reading the TOC (table of contents) of all my disks. At first I thought the disks were bad and erased a couple. However, for a test, I popped a disk into one of my son-in-laws small pocket size portable players and they did fine. Do you know why a unit might stop reading the TOCs? And is it an expensive fix?
This sort of problem is usually down to laser failure - even if the laser current alters, and it can be adjusted back to where it should be, it's a sign that it's on the way out anyway. I think that you'll need a Sony agent - the parts aren't so easy to find, and are a right pain to install. The real problem now is that Sony don't appear to be making any new table-top models. I was rather hoping that they'd do a HI-MD one, but they don't appear to be.