Rockwell Automation Publication 7000-UM202H-EN-P - November 2023 79
Chapter 2 Power Component Definition and Maintenance
Figure 72 - SCR snubber Circuit Connections
SCR Anode-to-Cathode Resistance
Performing an anode-to-cathode resistance test verifies the integrity of the
SCR. The SCR uses the snubber circuit to power the self-powered gate driver
boards. The resistance measurement taken across each SCR should be
constant; an inconsistent value may indicate a damaged sharing resistor, self-
powered gate driver board or SCR.
Using an ohmmeter, measure the anode-to-cathode resistance across each
SCR in the rectifier bridge, while looking for similar resistance values across
each device. Easy access from the anode-to-cathode is available by going from
heatsink-to-heatsink (Figure 73
).
SCR Resistance Measurement
Measured Resistance
Inverter Rectifier (SCR only)
SCR Anode-Cathode Resistance (heatsink to
heatsink) k-Ω
(Lowest) (Highest) (Lowest) (Highest)
SCR Gate-Cathode Resistance (across SCR
Phoenix connector) Ω
Snubber Resistance (Test point: heatsink
above) Ω
(Lowest) (Highest) (Lowest) (Highest)
Snubber Capacitance (Test Point – heatsink
on Right) µF
(Lowest) (Highest) (Lowest) (Highest)
Sharing Resistance (Red wire from snubber
Phoenix connector—heatsink on left) k-Ω
(Lowest) (Highest) (Lowest) (Highest)
To Gate Driver Board
Heatsink
Heatsink
Snubber
Resistor
Snubber
Capacitor
Sharing Resistor
Test Point
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