[teamjnz]

Hello,

I am need of some technical help for testing an older 1994 Haas with DC servos. I got a 175 alarm... This is what I have done so far. I went into the parameters and disabled the x y and z drives, released the e-stop and pushed the reset button a few times, no alarm. Enabled the Z axis, no alarms. And then enabled the y axis, no alarms. Then the x axis, alarm 175. Disabled x again and the alarm was gone. So I turn of the machine and power off too. I blew all the carbon dust out of the servo brush holes. The servo motor was clean and dry. The brushes have no sign of coolant or anything else getting into the motor. I put everything back and re-enabled the x axis and still have the 175 alarm.

I was given instructions to unplug the servo wires from the drive to isolate the drive from the motor to see if the alarm returns. I from what I understand this will let me know if the alarm is in the drive or the motor. If the drive is fine I would like to ohms test the motor but I don't know what the reading range should be.

Does anyone know? This information would be great. I can test the others and compare to see if there is a big difference or not.

Thanks

[teamjnz]

This is what I did tonight..

I disconnected the black and white wires from the x axis card and turn on the machine. No alarms.

When I turn on my (Klein Tools from Home Depot) multi meter to OHMs the reading is 0.L and when I touch the read and black leads together it reads 000.0

X axis OHMs test
I took an OHMs reading with the black and white wires 1.6 was the reading
White to ground 1.6
black to ground 0.0

Y axis OHMs test
white and black 1.6
white to ground was doing something different and settle on 40.3 for a moment and the to 0.L
black to ground was similar, take a reading and then go to 0.L
something was weird with this so I proceed to Z axis

Z axis OHMs test
white and black 1.2
white to ground 1.019
black to ground 1.018

retested Y axis after the Z axis
white and black 1.6
white to ground 0.L
black to ground 0.L

All of the white and black wire were connected again and I powered up the machine and got the 175 alarm. Powered off again and disconnected only the white and black wire on the X drive board and powered up again, no alarm.

Any thoughts?

Thank you

[Jim Dawson]

The X motor black to ground reading does not seem correct. Looks like it might be shorted. The Z axis readings seem odd also. Are you sure that the Z reading were not K ohms or Meg ohms?

[teamjnz]

The X motor black to ground reading does not seem correct. Looks like it might be shorted. The Z axis readings seem odd also. Are you sure that the Z reading were not K ohms or Meg ohms?

I am assuming it is K ohms since it is a standard multi-meter. I was told a meg ohm meter is a special tool.

- - - Updated - - -

Ok more info. I needed to remove the motor so I could take off the cover to disconnect the motor wires. I disconnected white and black wires from the drive board and the motor end. (Unplugged the white and black from the red and black motor wires.)

All of the test below are with OHMs readings

With the motor unplugged I tested both white and black wires together the reading was 0.L from the drive board side and motor side and the readings were 0.L. Then I tested the white wire to ground from both side and got the same reading of 0.L. I tested the black wire to ground from both side and got the same reading of 000.0.

Now I repeated the testing I did yesterday with the motor plugged in and the drive board disconnected. From the drive side white and black together read 1.5. White to ground 1.5. Black to ground 000.0

From the motor side, unplugged from the motor, and the white and black connected to the drive board. White and black together read 7.01. White to ground 7.00. Black to ground 000.0

At this time I placed the motor on some cardboard so the motor isn’t touching any metal. (Looks like didn’t need to do that because I got the same reading when I touched one of the meter probes to the machine casting and the motor housing.) I checked the motor wires red and black together 1.4. Black to ground 39.7, red to ground 39.7

Hopefully this will tell us something.. J Again I really appreciate all of the help

[Al_The_Man]

The normal resistance of that size of servo is a very low Ohm value across the leads, and open circuit or very high Resistance to frame.
You can test the motor to some limited degree with a automotive battery in either direction for rotation, also shorting the leads together and try and turn the motor shaft should offer resistance to turning, (braking effect)
In some cases carbon dust builds up and causes tracking to motor frame which can be a cause of ground connection.
Al.

[Jim Dawson]

A megger is a special meter for reading insulation leakage, or system grounding. But most modern DMMs will read several megohms.

On your meter a reading of 0.000 means no resistance, ie. a dead short. I think 0.L means open or no connection at all. With the motor disconnected, between any wire and the motor case it should read 0.L, there should be no connection between the motor windings and the motor case.

The reading of 1.4 between the red and black wires seems about right, but the 39.7 to motor case is not right, I would expect that to read 0.L. That indicates a short. As Al stated above, it could be carbon from the brushes creating a short.

You are probably going to have to open the motor up and give it a bath. You can use the non-flammable brake parts cleaner in a spray can from your local autoparts store. DO NOT use the flamable stuff, it is lacquer thinner and may damage the insulation on the windings. The non-flamable stuff is tetrachloroethane and is safe for the insulation and other electrical parts. If that doesn't fix it, then a trip to your local motor shop would be in order I think.

[haastec]

The normal resistance of that size of servo is a very low Ohm value across the leads, and open circuit or very high Resistance to frame.
You can test the motor to some limited degree with a automotive battery in either direction for rotation, also shorting the leads together and try and turn the motor shaft should offer resistance to turning, (braking effect)
In some cases carbon dust builds up and causes tracking to motor frame which can be a cause of ground connection.
Al.

+1 Measuring each wire leg to the casting or arbor of the motor, this should read an open circuit under ideal conditions. My rule of thumb has always been that any reading below 1Meg ohm from each leg to motor casting means the motor is on its way out or will need servicing soon.

As Jim mentioned, you will most likely need to disassemble the motor to give a thorough cleaning and once over. This can buy you anywhere from months to years of continued service, if you still have the same alarm, I would suggest replacing the motor.