I would really appreciate anyone's help with this one. I have been trying to fix a Bridgeport series 2 milling machine for a friend of mine for this past couple of weeks but now I have hit a wall. There were various different problems with it like RC filters burned out, diodes burned on the MTI-1 card and a transformer burn out on one of the axis driver cards, all of which have been repaired and are working. The problem that I am stuck with now is the spindle wont start when we launch the M03 program and I have noticed that as soon as the machine powers up the tacho loss led 11 lights up on the FAC-1R card and stays lit, is that normal? So far what I have found is that when we launch the M03 program I am getting 24v out of J2/10 on the TNC Unit and going into terminal 23 on the MTI-1 card for a couple of seconds. This 24v is supposed to go through relay RL3 on the MTI-1 card and come out on terminal 22, which then turns on contactor 15CR which activates the spindle, the problem is that RL3 is not been told to switch on. In order for relay RL3 to energize I would need 0v on terminal 12 as the other end of its coil is tied to a constant 24v. On my terminal 12 which is connected to terminal 14 on the FAC-1R card I am getting 24v, and this is as far as I have got. Would the fact that I am getting an "Tacho Loss alarm" on the FAC-1R card prevent it from giving the command to start the spindle? I have checked the tacho and it looks good, all four brushed are clean and have minimal ware. The resistance looks normal through the windings and I am seeing the same resistance on terminals 6 and 8 on the FAC-1R card. In order for the tacho to generate any sort of voltage the spindle has to rotate, correct, so why is there a tacho loss alarm even though my spindle hasn't moved?
If anyone out there can help me out I would really appreciate it.

Thanks,

Larry.

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