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Section 5
Troubleshooting
Troubleshooting 5-1MN894
Safety Notice Be sure to read and understand all notices, warning and caution statements in Section 1
of this manual. If you have any questions about the safe operation of this equipment,
please contact your Baldor representative before you proceed.
Preliminary Checks In the event of trouble, disconnect all input power to the control and perform these
preliminary checks.
Power Off Checks
1. Check all connections for tightness and signs of overheating.
2. Check for cracked or damaged insulators and terminal blocks.
3. Ensure the correct setting of the overload relay.
4. Check the fuse in the control transformer.
5. Perform the SCR resistance test for all SCR’s.
6. If a shorted SCR is suspected, check for possible shorted connections, system
grounds or any other condition which may cause the short circuit condition.
7. Replace the SCR pack or power cell if no other causes were found. However,
installing a new SCR pack or power cell without determining the cause of failure
can result in repeated failure of the SCR’s. Refer to SCR replacement
procedure in this manual.
Blocking Voltage Check This check need only be performed if the resistance checks of the power cells or SCR
packs (55 and 80 amps) are inconclusive.
WARNING: Before power is applied to the control, be sure there is no danger to
personnel or equipment if the motor shaft rotates when power is
applied. A shorted SCR or damaged control can cause abnormal
operation of the motor.
1. Be sure power is off. Disconnect the load from the motor shaft if possible.
2. The T1, T2 and T3 motor leads should be connected to the control for this test.
3. Disconnect one of the wires at the shunt trip contact on the control to prevent
operation of the disconnect circuit during this test.
4. Apply power to the control.
5. Measure the voltage from the line terminal to the load terminal on each of the
power phases. The voltage should be about 0.58 times the input line to line
voltage. If the voltage on any power cell or SCR pack is significantly less than
this value, one or both SCR’s in the power cell or SCR pack may be shorted.
6. Remove all power to the control.
7. If a shorted SCR is suspected, check for possible shorted connections, system
grounds or any other condition which may cause the short circuit condition.
8. Replace the SCR pack or power cell if no other causes were found. However,
installing a new SCR pack or power cell without determining the cause of failure
can result in repeated failure of the SCR’s. Refer to SCR replacement
procedure in this manual.