Tormach spindle speed control is done at the computer end by generating a series of pulses that are sent to the control board inside the mill's electrical cabinet. The width of these pulses remains constant while the frequency varies. On the control board those variable frequency constant width pulses get integrated (i.e. filtered) into an average DC voltage. That average DC voltage is what goes to the spindle drive inverter to command the spindle speed. When you switch to manual spindle speed control the spindle speed control on the control cabinet front panel gets selected as the spindle speed control going to the spindle drive inverter input, and the control board average DC spindle speed control output gets disconnected.
Based on the symptoms that you have indicated, any of the following could be at fault. If I was there with one of my oscilloscopes I could help you determine which one of these is at fault, but that is not the case so an indirect method must be used instead.
You need to check the pulse output coming from the computer, inside the mill's electrical cabinet where it enters the control board. When the spindle is being commanded to run you should see a pulse train there, and the frequency should vary with the commanded RPM (higher RPM = higher frequency).
1. If this pulse train does not exist then:
1.A.1 The mill connector end of the interconnecting cable could be at fault.
1.A.2 Or the interconnecting cable from the computer to the mill could be at fault.
1.B.1 The computer connector end of the interconnecting cable could be at fault.
1.B.2 The source of that pulse train inside the computer could be at fault. This pulse train is generated by the Path Pilot card.
1.B.2.A The Path Pilot software is not functioning correctly.
1.B.2.B Or the Path Pilot card is defective.
2. If the pulse train exists but the frequency does not vary with different commanded spindle speeds then:
2.A The Path Pilot software is not functioning correctly.
2.B Or the Path Pilot card is defective.
If the pulse train exists and the frequency varies with command RPM changes then check the output signal on the control board going to the spindle drive inverter.
3. If the average DC voltage does not vary with commanded RPM changes then:
3.A If the output is stuck at some solid voltage level (including ground, if the output is at zero volts) then there is a short:
3.A.1 On the control board.
3.A.2 Or in the interconnect to the front panel switch or the spindle drive inverter.
4. If the average DC voltage does vary with commanded RPM changes then:
4.A The average DC speed control voltage from the pulse integrator going to the spindle drive inverter is not making it through the interconnect to the spindle drive inverter. Check the same signal at the control panel Manual/Auto spindle speed control selector switch.
4.A.1 If the correct signal does not exist at the input to the switch then the interconnecting cable is at fault.
4.A.2 Or if the correct signal exists at the input to the switch but not the output when the switch is toggled, the switch is defective.
The above list is not completely exhaustive but it should be sufficient to debug your problem. You will have to refer to your Tormach mill schematics to find the correct test points to examine. My Tormach is quite old (late series I with Mach 3) so I doubt that the schematics would agree.