[fordav11]

I don't know anything about your issue, but heating something up to 'fix' it is a classic problem of either dry solder joints or bad capacitors. probably not related in this case but I just thought I would mention it :-)

[underthetire]

Never run in to that one. I'd say off hand its the tacho unit speed sensor in the motor. Only way I know to check those is with a scope.

[WC56]

Hello again. I tried the heater thing again today with the same results...the machine runs fine once the spindle motor is warmed. Underthetire, can you tell me anymore about this tach unit speed sensor...where it is, what it does etc? The tech said I needed to get the warmth to the back of the motor?

I think we are on the right path because when the heater is turned off for 1/2 hour or so the problem starts to return. Turn the heater back on & it goes away again. The machine is not actually cutting anything, just running through a test program.

I did notice today that M04 started working before M03 (needed a bit more heater time) Any thoughts?

[underthetire]

There is a toothed trigger wheel on the back of the motor. It has an inductance sensor that provides velocity feedback to the drive. So either the sensor is dirty, out of adjustment, or just plain bad. Check the motor bearings as well, if the rear one is bad it can cause sensor gap issues.

[WC56]

Ok, looks like the next step is to pull the motor out & have a look. Thanks again

[WC56]

Well I finally got time to pull the motor out. The bearings all feel good but when I checked the magnet in the sensor it wasnt overly strong. Funds are a bit tight at the moment so I cleaned & reinstalled the sensor with a little less clearance. She is running well again, but for how long I cant say. At least I got the numbers for the sensor (its a Fanuc A20B-9000-0010), so will keep a look out for a good one.

Thanks for the help guys.

[doctorcnc]

The Fanuc analog spindle drives (that use A20B-0009-053x & similar control cards) have two pots that calibrate the incoming encoder signals for 50% duty cycle of the sine waves. If these signals get out of calibration, the drive will make the motor spin erratically or not spin properly at all. To check, command the drive to spin the motor (or just spin the motor by hand if the drive is just alarming out) and use a scope to look at the signals on CH 7 & 8 (bottom of board, near encoder connector). Adjust RV 18 to set CH7, and adjust RV19 to set CH8.

Jim, cncrepair.com

[WC56]

Thanks Jim you were spot on with your information. I made the adjustments as you described & everything is working great again. I'm appy to have this problem solved at last.