Rockwell Automation Publication 7000-UM202H-EN-P - November 2023 85
Chapter 2 Power Component Definition and Maintenance
Replacing SCR and SCR Self-Powered Gate Driver Boards (SPGDB)
Replacing the SCR is similar to replacing the SGCT, except that you can replace
the SCR and circuit board independently of one another.
1. Isolate and lock out all power to the drive.
2. Note the position of the fiber optic cables for reassembly.
3. To remove the SCR and SCR SPGDB, first remove the gate driver power
supply connector (from snubber circuit), the fiber optic cable, and the
SCR gate-cathode connection. Exceeding the minimum bend radius
(50 mm / 2 in.) of the fiber optic cables may result in damage.
4. Remove the load on the clamp head assembly as described under
Checking Clamping Pressure
on page 88.
5. Loosen the 2 captive screws with a long Phillips screwdriver until the
circuit board is free. If necessary, adjust the position of the heatsinks to
allow free movement of the SCR.
6. Slide the SCR and SCR SPGDB straight out.
7. While grounded, unplug the gate-cathode connector from the SCR SPGD
board.
To replace the SCR, follow steps 8…11 and 15…18.
To replace the SCR SPGDB, follow steps 12…18.
8. Loosen the tie wrap holding the gate-cathode wire in place, and remove
the device from the assembly.
9. Install the new device in the same position and using the same
orientation as the original SCR, and firmly secure the gate-cathode wires
with the same tie wrap.
10. Connect the gate-cathode connector to the gate driver board.
11. Apply a thin layer of electrical joint compound (Alcoa EJC No.2 or
approved equivalent) to the contact faces of the new SCRs. The
recommended procedure is to apply the compound to the pole faces
using a small brush and then gently wiping the pole face with an
industrial wipe so that a thin film remains. Examine the pole face before
proceeding to ensure that no brush bristles remain.
ATTENTION: To prevent electrical shock, disconnect the main power before
working on the drive. Verify that all circuits are voltage-free using a hot
stick or appropriate voltage-measuring device. Failure to do so may result in
injury or death.
ATTENTION: You may damage the fiber optic cables if you strike or bend
them sharply. The minimum bend radius is 50 mm (2 in.). The connector has
a locking feature that requires pinching the tab and gently pulling straight
out. Hold the component on the printed circuit board to prevent damage.
ATTENTION: Static charges can destroy or damage the SCR and SCR SPGD
board. Properly ground yourself before removing the replacement SCR and
SCR SPGD board from the protective anti-static bag. Using damaged circuit
boards may also damage related components. Use a grounding wrist strap
for handling sensitive circuit boards.
IMPORTANT Never adjust the orientation of the SCR using the gate and cathode leads.
These connections are sensitive; adjust the device orientation by turning
the device itself.
IMPORTANT Too much joint compound may result in contamination of other surfaces
leading to system damage.
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