I found 1 post from 2010 in search but did not resolve my issue. Anyway..

This machine is a mid 80's LB15 OSP5000-G control.

Problem: Z axis alarm out with 100-4 diff error. (Usually when cold. Machine does better at running temp)

When I move the machine manually (pulse wheel) I can feel the axis motion stop. When the axis stops the Z motor is showing a 120% load. On the "Extend Data" servo screen I can verify the DIFF error... Of course if I keep going it will eventually alarm out due to the tracking difference.

What I have done so far:
1. Checked lubrication
2. Checked for mechanical issues
3. Checked cabling
4. swapped the motor
5. swapped the SVC board
6. swapped the Drive
7. swapped the drive power supply
(luckly we had an old machine we parted out. However the parts ARE used.)

Right now I'm still getting the same issues. No better/No Worse. Any other ideas?