Watlow QPAC Modular SCR Power Control Service - Manual (Page 17)

WATLOW QPAC Service Manual 17 Troubleshooting, Chapter 5
Procedures
Chapter 5
Troubleshooting
Indications of Malfunction
1. No output under any circumstances.
2. Full ON output at all times and the load is uncontrollable.
3. Output is not proportional to the command signal (unbalanced output).
4. Operating erratic and inconsistent.
5. Half output.
6. One or more LEDs not lit on the Q33 base
Troubleshooting Guidelines
Troubleshooting the QPAC should be limited to changing fuses, transformers, SCRs
and printed circuit boards. Any other troubleshooting should be done on a test bench
and by a qualified electronic technician capable of working on high voltage.
WARNING:
When working on a power control, caution must be used as high voltage is
present when power is applied.
On power bases of 100 amps or less, the heat sinks should be at ground
potential. Units above 100 amps are electrically hot.
Before troubleshooting, make sure you have isolated the problem to the QPAC.
Make sure all connectors and load terminations are tight and the control card is
seated properly. Next, verify that there is AC power present at L1 and L2. For
three phase units check at L3 by measuring phase to phase. Phase to ground is
meaningless on ungrounded three-phase loads. Verify that there is a good com-
mand signal (i.e. 4-20mA) from the temperature control, and that the temperature
control is operating properly.
Troubleshooting the QPAC can be narrowed down to three distinct problems.
•
Unit has no heat
• Unit has partial heat
• Full or partial uncontrollable heat
Once you have determined the category that best describes your situation, read
through the appropriate section on the following pages. Follow the procedure
which applies to you.