-- Having finally tired of trying to fix the Z mechanims, I requested a single replacement rod from MakerBot, since I know at least one rod is bent to the point of being defective. They returned with two free rods almost immediately, so that is a good sign.
power supply failed !
I notice that MakerBot is selling a PSU for $35 that is available for $18 on Amazon. This particular unit is apparently not particularly reliable. Thankfully, a computer repair shop across town had a used supply and I was able to get the bot up and working in a couple hours