10-12 Troubleshooting
1560D-UM051D-EN-P – February 2005
Power Circuit Thyristor Testing
Troubleshooting
If a power semiconductor is suspected of malfunctioning, it may be
checked as follows:
1. Remove all power from the equipment.
To avoid shock hazard, ensure the main power has
been disconnected before working on the controller,
motor or control devices. Verify that all circuits are
voltage free using a hot stick or appropriate voltage
measuring device. Failure to do so may result in burns,
injury or death.
2. Measure DC resistance per the following chart:
Location of Probes 1000 V 1300 V 1500 V 2300 V 3300 V 4160 V 5500 V 6900 V
Cathode to Cathode (KOhms) – – – – 22-30 23-31 21-29 24-32
Cathode to Cathode (KOhms) 17-23 19-25 20-27 21-29 40-53 43-57 60-80 Z 64-84
Cathode to Gate (Ohms)
10-40 10-40 10-40 10-40 10-40 10-40
10-40
10-40
Measured between terminals “Cathode” on SPGD Boards, upper two or bottom two within a phase.
Measured between terminals “Cathode” on SPGD Boards, top to bottom within a phase.
Measured between line and load terminals within a phase.
Note: The actual resistance value depends on the ohmmeter used, the
particular brand/rating of thyristor, and external circuit influences.
It is impossible to accurately measure the condition of the thyristor
when it is unclamped!
3. If a short circuit is suspected, the thyristor must be isolated from all
surrounding circuitry (i.e. unplug gate and cathode leads, and remove
snubber and resistor circuit leads from the driver boards). Measure
resistance to confirm state of the thyristors. If the thyristors are not
shorted, proceed to snubber and resistor circuit testing, following this
procedure.
4. If a faulty device is found, the entire heatsink assembly must be removed.
For heatsink assemblies containing four or more
thyristors, the entire matched set shall be replaced.
Devices connected in series must have performance
specifications matched for proper operation. Failure to
use matched sets may result in damage to the devices.
5. Complete heatsink assemblies with matched thyristors are available as
a renewal part (see Appendix C). In most cases, the assembly can be
dismantled to replace the SCRs.
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