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Troubleshooting 5-3MN894
Resistance Test Disconnect the power cell or SCR pack from all external wiring before you perform a
resistance check. Use an ohmmeter with 20,000 ohms per volt or greater impedance for
the resistance measurements. Refer to Table 5-1 and Figure 5-1.
1. Be sure power is OFF.
2. Remove all wiring from the power cell or SCR pack.
3. Sizes 55 and 80 amps have three SCR packs, one for each phase mounted on
a single ground potential heatsink. Check all three SCR packs. For example
L-GL must be measured from L1-GL1, L2-GL2 and L3-GL3. Circuit SA-SB
requires only one measurement.
4. Sizes 160 through 840 amps have a separate power cell for each phase.
Check all three power cells.
5. If any of the resistance measurements are incorrect, the power cell or SCR
pack should be repaired or replaced before operating the starter.
Table 5-1
Circuit Resistance
L-A
T-B
SA-SB
Less than 5 Ohms
A-B Greater than 10k Ohms
L-GL
T-GT
5 to 100 Ohms
Note: Results from the resistance measurements can be satisfactory and the power
cells may still be bad if the power cell is breaking down under voltage.
If resistance checks are not conclusive, perform Blocking Voltage Check and SCR Full
Voltage Test.
Figure 5-1 Power Cell Configurations