How to Test a Servo Motor
If you need to test a servo motor and have a quality ohm meter or megaohm (at least 10 mo) handy, we've provided a few basic steps to assist. Although it may go without saying, disconnect all power to the machine before you begin otherwise you could wind up with a permanent wave in your hair in the very best case scenario.
Using an Ohm Meter
Disconnect ONLY 3-phase motor lines (T1,T2,T3) from the drive. Test while the cable is still connected to the servo motor first. As long as the reading is infinite, there is no issue. However, if the reading is 0 (zero) or if there is any continuity, you can be sure that a problem exists. Now disconnect the cable and test the servo and the cable separately. Make sure that the leads on both ends are not touching anything, including other leads.
Using a Megaohm Meter
Test all three wires (T1,T2,T3) separately. You're looking for readings ranging from 600 to 2000 megaohms since most shorts fall below 20 megaohms. Make sure not to touch the leads or the wires while taking the readings since false, unrepeatable readings can lead to redundancy. Rule of thumb: About 1000 ohms of resistance for each volt of power is about the average for 230VAC 3-phase motors. Readings between 230meg and 600meg reveals that there is some deterioration in either the cables or the motor insulation.
Test for Open or Short in Windings Using an Ohm Meter
Test the connections from T1 to T2; T2 to T3; then T1 to T3. The expected range for each is between .3 and 2.0 ohms with .8 ohms being about average. If you get a 0 reading, there is a short between the phases. If the reading is infinite or above 2000 ohms, it is an open.