[m0602233]

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!

[m0602233]

Pdf attached.
I guess what I would like to know is what else could cause the tacho loss led to light up?

[m0602233]

Okay so I have narrowed it down to IC5 and IC6 which are in loop supposed to multiple signal frequency from 50Hz to 300Hz for 6 thyristor circuits. It looks like that those IC:s are missing oscillator Vss (0v). I guess it can be fixed after all.

[Docter Don]

Yeh the Tach Loss generally means the drive tried to send current to the motor but not seeing any tach voltage in response. This often is due to failure in the drive itself, as you are now seeing. Are you seeing the 50Hz at TP2 and TP3? But no 300Hz at TP4?

[Docter Don]

Also, you said the Field Ready LED extinguishes. Is that saying that the field supply stopped sending current to the field due to the Tach Loss, or due to a failure of the supply itself? What model of Spindle drive is this? I'd need the full drive schematics to give more input. Maybe a link to an online form of the manual instead of all the pages of the schematics would be good.

[m0602233]

Yeh the Tach Loss generally means the drive tried to send current to the motor but not seeing any tach voltage in response. This often is due to failure in the drive itself, as you are now seeing. Are you seeing the 50Hz at TP2 and TP3? But no 300Hz at TP4?

I am seeing 50hz at tp2 only, after that nothing. Also at tp2 should be 15v square wave but it is only about 8,4v square wave. Ic5 and Ic6 are phase-locked loops (cd4046bc). Ic6 is for adjusting phase with potentiometer and Ic5 is frequency multiplier. Tp2 comes from comparator Ic4.

Unfortynately I have not been able to find circuit diagram for this drive. It is KTK Thyristor Drives FAC-1R Iss.5

[m0602233]

Also, you said the Field Ready LED extinguishes. Is that saying that the field supply stopped sending current to the field due to the Tach Loss, or due to a failure of the supply itself? What model of Spindle drive is this? I'd need the full drive schematics to give more input. Maybe a link to an online form of the manual instead of all the pages of the schematics would be good.

https://1drv.ms/b/s!Am1Uj4kzNQg-hKFgGaNB1H_38ggjTw
Link to manual above.

[m0602233]

I replaced ic4, 5 and 6 yesterday and it might have solved the problem. I think ic6, 4046 PLL, was faulty. It seemed to be somehow leaking some of the signal to ground via its zener or something. I could measure some square wave from its pin 15 which is not supposed to be connected to signal in.
Thanks Don for helping, I was almost sure this repair was above my skill level but I guess you and others here could have helped in that case