GE Industrial Solutions ASTAT-CD Plus Solid-State Starters - Manual (Page 17)

ASTAT-CD Plus Service Instructions
17
Figure 13. SCR and heatsink assembly
Step 27. 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. Retain the
gate and cathode leads from the SCRs for use
when reassembling the SCRs and heatsinks.
CAUTION: Do not adjust or move the pre-set nut
(6) (Figure 13). The pre-set nut (6) and the
belleville 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.
Step 28. Clean both heat sink surfaces with a fine
abrasive such as Scotchbrite, then remove all
particles from the surface of the heatsink. To
clean the SCR, wipe the SCR mounting
surfaces with a mild solvent.
Step 29. Apply a light coat of thermal compound such
as Electrolube 2 GX 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
backward and forward by hand applying firm
pressure to the SCR. Remove the SCR from
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
the heatsink, the mating surfaces must be
uniformly coated with thermal compound. If
the mating surfaces are not coated evenly,
apply slightly more thermal compound to the
surfaces and twist back and forth as before.
Step 31. With the (2) SCRs located properly on the
heatsink, i.e. the gate and cathode terminals
on the SCRs must be on the proper side of
the heatsink assembly (as disassembled),
place the other heatsink over the SCRs.
Refer to Figure 13.
The clamp is assembled so that the cross
piece (5) with the pressure plate (4) and the
tension bolts (10) are at the top. Underneath,
the cross piece (3) with the pressure plate (4)
is put in position and the two tension bolts
(10) are alternately tightened carefully until a
slight resistance is felt. Check that both cross
pieces (3) and (5) are parallel. For this check,
it is sufficient to check that the tension bolts
project equal distances beyond the cross
piece (3)
. The tension bolts (10) may now be
alternately tightened 1/4 turn at a time until
the metal gauge (8) can be easily moved.
Note - The tension bolts should not be
tightened beyond the point that the metal
gauge (8) can be easily moved. Never adjust
or change the position of the preset nut (6).
The preset nut (6) determines the clamping
force applied to the SCR.
Light
+
+
-
-
S2
S1
20 Ω
1W
(SCR)
Cathode
Anode
Gate
(~.15AMP to .20AMP LOAD)
5VDC
Figure STC
SCR Test Circuit
Remove all power from ASTAT-CD Plus
Test SCR's only when clamped in heatsink assembly.
With S1 closed and S2 open, the lamp should be off.
If lamp is on, SCR is shorted.
With S1 closed and S2 closed, the lamp should turn on.
When S2 is opened, lamp should stay on. SCR is good.
SCR must be disconnected from ASTAT-CD Plus control (yellow and blue
leads disconnected from SCR) and no load connected to ASTAT-CD Plus.