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Fanuc Yaskawa Daito Fuses
Fanuc Fuses | Yasnac fuses

Megger for testing Servo motors
Servo motor megger, megohm meter

Servo Motor (3phase 220vac) testing:

Below are some basic principles for testing servo motor circuits with meter or megohm meter. This procedure will show you how to test for shorts in windings, cables or opens. But before starting turn off all power sources to machine then disconnect the 3- phase motor lines ONLY from the drive. Check the cable along with the motor at the same time to cover everything, if this turns out good then all is usually well. Diagrams not available yet .

Fanuc Servo Motor

Testing for short to ground
Using Ohm meter:
Disconnect all power from machine. Check all three wires singly T1,T2,T3 (all three phases) to the ground wire. Readings should be infinite. If its zero or reads any continuity

at all, then a problem exists with either the motor or cable . If it is go directly to the motor and disconnect from cable and check motor and the cable separately. Be sure to make sure leads on both ends are not touching anything including the other leads. Most servo motor shorts can be read with a regular quality meter. Make sure you use quality meter going up to at least 10megohms

Using Megohm meter:
Disconnect all power from machine.
Check all three wires separately T1,T2,T3 (all three phases) to the ground wire. Readings are usually in a range from 600-2000 Megohms. Most shorts will be below 20 megohms. Be careful not to touch the leads or the wires to anything when taking the reading. It can give false and unrepeatable readings causing you to chase your tale. The above is what I found to be the average for 230VAC 3 phase motors. A rule of thumb that I've come across in other reference materials is about 1000 ohms of resistance for each volt of incoming power. Though 230meg for a 230VAC circuit seems on the low side from my experience. Only use this as a rule of thumb. Just beware that from 230meg to 600meg often shows some deterioration in the cables or motor insulation.

Testing for Open or short in windings:
Ohm meter for testing

Using Ohm meter:
Disconnect all power from machine.
Put meter on ohms
T1 to T2
T2 to T3
T1 to T3
Range usually expected .3 to 2.0 ohms
Most are about .8ohms.
If zero-a short between phases exists
Usually if it is an open its infinite or well above 2K ohms

Cable and Plug Notes:

Often times the connector on the cable to the motor will get coolant in it. Try drying out and retest. If it is still bad the inserts themselves get burn marks in them and cause a slight short and should be replaced.
Also look for areas where the cable moves through tracking. Wires will wear through

If its a DC Motor check the brushes. There should be 3-4 round caps to remove around the motor. Under these you will find a spring with a square block (brush). See how much is left maybe need to replace. Also check the commutator that the brushes ride against for wear. Try wiping surface.