Allen-Bradley SMC-50, User Manual

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172 Rockwell Automation Publication 1560F-UM001A-EN-P - June 2019
Chapter 9 Troubleshooting
B. Replace SCRs
1. Remove the shorting bar. Measure the resistance between adjacent
heatsinks to determine which SCR(s) is (are) shorted. Assemblies with
four or six SCRs must use matched sets. See Figure 56 and Figure 62 for
the position of the matched sets. If an SCR from each set is shorted, all of
the SCRs in the module must be replaced. A properly functioning SCR
will measure in excess of 100 kohms from anode to cathode, and 10…40 Ω
from gate to cathode.
2. Loosen the clamp by rotating the center nut below the indicator washer at
the top end of the clamp. Refer to Figure 54 , Figure 57 and Figure 63 .
As the center nut is rotated, the entire spring assembly is retracted from the
top heatsink. Continue to retract until there is a gap of approximately
6 mm (0.25 in.).
3. The heatsinks may now be spread apart to allow removal of the SCRs.
4. Apply a thin film of Electrical Joint Compound (supplied) to both faces of
the new SCRs.
5. Place the new SCRs in position starting from the top and pushing the heat
sinks together as you proceed down the stack. Make sure the SCRs are
positioned and oriented properly. Refer to Figure 55 , Figure 58 , and
Figure 64 .
6. Ensure that the SCRs are properly seated on the locating pins in the
heatsinks and rotate each SCR so that the leads are oriented toward the
front right side of the assembly.
7. Advance the center nut until the spring assembly engages the top heatsink.
Make sure the clamp is properly seated on the locating pins in the top and
bottom heatsinks before beginning to tighten.
TIP For 600A units, it is mandatory that the entire stack be replaced. The high
clamping force requires the factory to tighten the clamp hardware. See
Appendix H, Spare Parts for part numbers. Proceed to step C.
TIP Refer to Figure 52 to Figure 64 .
• SCR positions are numbered in succession from the top down.
The SCR cathode is at the end with the wide flange.
ATTENTION:
The SCRs must be oriented correctly with the cathode end either
up or down, depending on the specific assembly. Note the orientation before
removing the SCRs, and refer to the detail in the appropriate figure in this
chapter.
IMPORTANT DO NOT
loosen any of the nuts on the fiber rods on either side of the
clamp bars. They must remain as they are to maintain squareness. See
Figure 54 , Figure 57 and Figure 63 .