After my machine died on me I tried off and on to trouble shoot it over a couple years. I actually considered offering it up for parts at one point. Recently I gave it another go and discovered to my great joy a ribbon connector had been partially dislodged from it's end connector. I'm not sure what all the ribbon does but for sure it supplies power to the Z truck although it is not directly connected to it. It originates in the base of the machine and terminates at a small circuit board just next to the Y truck motor. Anyhow, long story short I was getting a Z stall error. By removing the end connector and reorienting the ribbon I snapped it closed again and plugged it back in. Problem solved .... until I ran a test piece on my sled. Then, again to my delight I discovered the real issue. The location of this ribbon is very low on the head and over time it and a larger ribbon right above it had sagged enough to actually drag along the work piece as it moved. On my test it caught the end of my board and unplugged itself. Luckily no damage was done and the only work required was to plug it back in and give it some type of support so it won't happen again.
I hope my experience can save someone else the hassle. And by the way my machine is an older B model.