Drives Service & Support > 1336F > Fault Finder

Fault Number: 38
Fault Display: Phase U Fault
Fault Name: Phase U Fault
Description: A phase to ground fault has been detected between the drive and the motor in this phase.
Corrective Action: Disconnect motor from output of drive. If fault clears, replace motor or motor cables. If fault persists, need to check power modules or transistors, base driver board. Lastly, check LEM's.

Testing Base Driver Board:

ATTENTION: Disconnect and lock out power from the drive before disassembling the drive. Failure to disconnect power may result in death or serious injury. Verify bus voltage by measuring the voltage between +DC and –DC on Terminal Block TB1. Do not attempt to service the drive until the bus voltage has discharged to zero volts.

IMPORTANT: Before you remove connections and wires from the drive components, mark the connections and wires to correspond with their component connections and terminals to prevent incorrect wiring during assembly.

1. Remove power from the drive. Check for zero volts at TB1 terminals +DC and –DC, and check for absence of control voltage.
2. Remove the Main Control Board.
3. Unplug the connectors from the Gate Driver Board.
4. Set your meter to test resistance.
5. Test Fuses F1 and F3 for an open condition. Replace the Gate Driver Board if any fuses show an open condition.
6. Set your meter to test diodes.
7. Test VR1 – VR6. The following table shows meter connections at the components and ideal meter readings for those connections. Refer to the former illustration for meter connection locations.

Typical malfunction is shorted in both directions

8. Replace the Gate Driver Board if your readings do not match the table readings.

Testing the power modules:

Refer to the proper troubleshooting manual for your drive size specific measurements and testing.