General - Checking Servo Motor Phases

Checking Servo Motor Phases

Below is a way to check to see if a servo motor is damaged.

(NOTE: If this test passes, the motor is not necessarily a good motor; however, if it does fail, then it is a bad motor and needs to be replaced.)

The idea behind this test is to check the resistance between the phases. The resistance between phases should have similar values. And there should be no connection between either of the phases or between either of the phases and ground.

To Test: 
A PMAC servo motor will have at least 4 wires and may be named various things:

U

V

W

ground

or

1

2

3

ground

or

R

S

T

ground

Using a multimeter, measure the resistance between U and V, note the resistance.

Measure the resistance between U and W, note the resistance.

Measure the resistance between W and V, note the resistance.

Is the resistance between the phases approximately the same? They should be. The actual resistance is not as important, as noting that the values should all be very similar.

Measure from U to ground. Is there any connection between them? It should be completely open...infinite resistance.
Measure from V to ground. Is there any connection between them? It should be completely open...infinite resistance.

Measure from W to ground. Is there any connection between them? It should be completely open...infinite resistance.