GE Industrial Solutions ASTAT-CD Plus Solid-State Starters - Manual (Page 22)

ASTAT-CD Plus Service Instructions
22
MOV Heatsink SCR gate and
leads assembly cathode leads
Thermostat Bolts holding heatsink
assembly to housing
Figure 11. SCR and heatsink location
Step 26. SCR/Heat sink disassembly - Remove the
thermostat, mounting insulator and other
parts to allow disassembly of the clamps and
SCRs from the heatsinks (Figure 12).
SCR and heatsink
assembly
Clamp assembly
Mounting Plate
Thermostat
Figure 12. SCR and heatsink assembly
CAUTION: Do not adjust or move the preset nut
(6) (Figure 13). The preset nut (6) and the bevel
washers under the cross piece (5) are preset to the
required force for assembly and clamping of the
new SCR to the heatsink.
Step 27. Removing the SCRs (Figure 13) - Loosen the
tension bolts (10) alternately, 1/4 turn at a
time, on each SCR until pressure releases on
the SCRs. Remove bolts and clamps to release
the heatsinks. Note: record the position of
both SCRs (gate and cathode connectors on
the SCR) for reassembly.
Caution: Do not adjust or move the pre-set nut (6)
(Figure 13). The pre-set nut and the bevel washers
under the cross piece (5) are pre-set to the required
force for assembly and clamping of the new SCR to
the heatsink.
Note: The mounting surface of the heatsink
must be flat and clean (i.e., bare metal) and
the SCR surface must be clean. Thermal
compound must be coated on all mating
surfaces between the SCR and the heatsink.
Figure 13. SCR and heatsink assembly
Step 28. Clean both heat sink surfaces with a fine
abrasive such as Scotch brite, then remove all
particles from the surface of the heatsinks. To
clean the SCR, wipe the SCR with a mild
solvent.
Step 29. Apply a light coat of thermal compound such
as Electrolube 2GX to both sides of the SCR
and to both heatsink surfaces that mate to the
SCR.
Step 30. Make sure that the orientation of the SCR is
correct(as disassembled) and place the
contact face of the SCR over the locating pin
in the mating heatsink surface. Twist the SCR
10 Tension bolt
4 Pressure plates
5 Cross piece
6 Pre-set nut 8 Metal gauge
7 Belleville washers
3 Cross piece
9 Center pin
1 Heatsinks
2 SCR
11 Insulated sleeve