Watlow QPAC Modular SCR Power Control Service - Manual (Page 23)

WATLOW QPAC Service Manual 23 Troubleshooting, Chapter 5
Q32
The QPAC Mother Board is Bad
Refer to the mother board troubleshooting procedure on Page 28.
The T1 Load Connection is Open
If T1 is open at the heater, the leads will occasionally couple AC back, and turn on
L3 and T3 SCRs. Check the load with an ohmmeter at Q32.
Problem: Partial Heat
Incorrect Phase Rotation
The phase rotation must be “A-B-C”. Measure voltage T1 to T2, T2 to T3, and T3
to T1. If it is not within 2 to 5%, reverse any two “L” leads and try again.
One of Two SCRs Won’t Turn ON (Half Waving)
This is most likely a problem with the mother board. A gate signal may be missing.
Refer to the mother board troubleshooting procedure on Page 28.
The Gain Adjustment is Too Low
Recalibrate the bias and gain adjustments by following the procedure on Page 16.
There is an Insufficient Control Signal
Verify that the signal from the temperature control is correct (i.e. 4-20mA, 1-5VDC,
etc.) Refer to the control card section, or the control user’s manual.
A Partially Open Heater(s)
Check all the connections from the circuit breaker to the heater. Measure the
heater current. Next, measure the voltage across the heater. If voltage is present
and no current is flowing, there is a bad connection or heater. Disconnect the
heater from the power control. Check the resistance of each element. The resis-
tance should correspond with the heater KW rating. If not, replace the heater.