BENSHAW RediStart EXEXMVRMX3 Series, User Manual

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Ohm Meter Testing
8.7 Ohm Meter Testing
A few reasons for an SCR Test Procedure would be if the starter is receiving shorted SCR trips, current imbalance trips, or ground fault
trips - basically the SCR is not turning on properly. If any cards have been replaced, it is also recommended to do a BIST test (see BIST
testing). A ohmmeter will be needed to perform the following tests. For accurate results, it is important to use the same ohmmeter
throughout the tests and for each SCR in the starter. If all ohm readings are within specified limits, then the SCRs can be considered
good and this procedure completed.
8.7.1 Fuse Tests
Perform ohmmeter resistance across both power and control fuses. Verify fuses for continuity.
8.7.2 Shorted SCR Test
This will test the anode to cathode integrity of the SCR. Use the following table and figure to place the ohmmeter probes. You should not
need to remove components to perform the ohmmeter tests.
z
NOTE: Figure 49 is the heat sinks that are underneath the 3 separate cards. Place the leads of the ohmmeter on the heat sinks behind
the gate driver card.
If all values are greater than 50K ohms, proceed to the SCR Gate to Cathode Test. If an SCR measures less than 50K ohms but not 0
ohms, the SCR still may be good. Contact Benshaw for further assistance. If any of the recorded values are 0 ohms then one or more of
the SCRs in that phase has failed. An ohmmeter can only determine failed devices; an SCR tester is required to verify proper operation of
the device.
z
NOTE:
If at any time during this procedure it is necessary to remove any of the red and white SCR gate leads from the firing card,
care must be taken to insure that these leads are reconnected to the terminal they were removed from.
Alternative Shorted SCR Test
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8 - TROUBLESHOOTING & MAINTENANCE
Test Ohm Meter Reading Results Value
From position 1 to position 2
Greater than 50 k
W
Pass
Less than 50 k
W
Fail
From position 1 to position 3
Greater than 50 k
W
Pass
Less than 50 k
W
Fail
Table 17: Ohmmeter Position
Figure 49: Heat sinks