Today I decided to check the brushes on the Z axis motor. This required pulling the motor out of the machine. Brushes looked fine so I cleaned out the carbon dust and decided I'd test it on the X axis using the open loop battery box. Hookup is fairly simple. 0V (red & black) is hooked up to 1 & 2. Enable (yellow & green) is hooked up to 16 & 17. Encoder loop from velocity controller 21 & 22 must be removed. 5 & 6 are the tachogenerator voltage.
Attachment 423830
Unfortunately the Z axis motor ramped right up to 2500 rpm on the X axis. The X axis motor had barely moved in open loop. Obviously there was something different about the two motors. After carefully comparing the two I found a short on one pole of the tachogenerator to the body. Oddly both motors generated similar +/- voltages when tested. I used a little liquid electrical tape to correct the short. After the repair the Z axis motor behaved properly on the X axis.
Attachment 423832
Following the motor repair I swapped the axis drives. The Z axis drive performed correctly on on the X axis. At this point I am confident both motors work along with both axis drives are good but there is clearly something not right with the Z axis wiring. I suspect the tachogenerator wiring. The voltage looks ok but I didn't have time to check for a short to ground. That's the next thing to check. I guess.
I'm getting closer...