Some of these had the GE spindle drive and some had the Inland drive. If I remember correctly, there's a small interface board near the bottom of the right panel that measures the current flow in the DC motor's 90 volt brake. The brake must be energized to release and this board detects current flow in the windings of the brake and allows the spindle drive to start. You might want to find the wire numbers for the brake and see if there is 90V DC across the winding.
If that's all OK, check for a red alarm light on the GE spindle drive (if that's what you have).