Hello

I just bought an old Bridgeport cnc mill and it actually did work, for about 5 minutes. However after couple of test runs the spindle didn't start anymore. KTK drive board and MT1-1 boards seem to be unharmed (visually) and everything seems to be working until i input M03/04.
Spindle motor is not even trying, tacho loss led lights up and field ready led extinguishes.

I took the motor out and checked the tacho but it seems to be fine. Windings and coils are good. Also zero speed relay clicks if the spindle is rotated by hand. It actually looks like somebody has been trying to fix the problem already, some of coils had been replaced and the wires from tacho looked like new also.
Furthermore, MT1-1 board, Fac-1R board and thyristor board seem to be recapped. Some of the old capacitors came with the machine. In Mt1-1 board also some diodes and resistors have been replaced at some point.

System monitor shows voltages as expected, only it takes a little while after startup for voltages to settle down.

Thyristors are not shorted, spindle motor field and armature windings are showing reasonable recistance and are not shorted to ground. Motor overheating protection is good also.

The question is, now what?
I'm running out of ideas really. I have some service manuals for these boards and they are not covering this problem.
Do I really have to begin retrofitting already?

Thanks for your help!