Rockwell Automation Publication 7000-UM202D-EN-P - May 2018 87
Power Component Definition and Maintenance Chapter 2
SCR Gate-to-Cathode Resistance
One test that can be performed on SCRs that cannot be performed on SGCTs
is a Gate-to-Cathode Resistance Test. Performing a Gate-to- Cathode
resistance measurement will identify damage to an SCR by revealing either an
open or shorted gate to cathode connection. To test an SCR from gate-to-
cathode, disconnect the SCR gate leads from the self powered gate driver board
and measure the gate-to-cathode resistance on the SCR firing card Phoenix
connector.
Figure 77 - SCR Gate-to-Cathode Test
The resistance value from gate-to-cathode should be between 10…20 Ω. A
value close to 0 Ω indicates that there is an internal short in the SCR. An
extremely high value indicates that the gate connection in the device has
broken.
If a Gate-to-Cathode test reveals a damaged SCR, see page 90
for the SCR
replacement procedure.
Test points for Gate-to-Cathode
Disconnect SCR
Phoenix
connector from
board
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