Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 141

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SCR REMOVAL AND REPLACEMENT (continued)
8. Place the new SCR between the heat sinks. Be
sure that the outer metal ring of the SCR is fac-
ing toward the same heat sink as the old SCR's
metal ring. Be sure that the roll pin of the heat
sink engages the "hole" in the SCR. The SCR
contact surfaces must sit flat against both heat
sink surfaces.
9. Clamp the SCRs to the output rectifier heat sink
assembly.
10. Two different designs of leaf springs and hous-
ings have been used to clamp the SCR to the
rectifier. The two different designs can be iden-
tified by the size of the leaf spring. One design
uses a 1/2" wide leaf spring and the other uses
a 5/8" wide spring. Follow procedure A below
for 1/2" springs. Follow procedure B for 5/8"
springs.
11. The different designs require different assem-
bly and clamping procedures, depending upon
the thread on the cap screws. A 1/4-28 thread
requires a different tightening procedure than a
1/4-20 thread. NOTE WHICH THREAD IS ON
YOUR CAP SCREWS BEFORE PERFORM-
ING THE ASSEMBLY PROCEDURE.
TROUBLESHOOTING AND REPAIR
FIGURE F.28 – 1/2" WIDE LEAF SPRING
Spring curvature exaggerated
SQUARE WAVE TIG 355
A. PROCEDURE FOR THE 1/2 INCH WIDE
SPRING:
1) Place a piece of sleeving around each
cap screw.
2) Insert the cap screws through the leaf
spring. Orient the leaf spring so that its
ends are curved upward toward the
cap screw heads. See Figure F.28.
Pressing on the cap screw heads
should produce a "rocking" motion of
the spring in its housing. If the spring
does NOT rock, it is installed upside
down. Remove the spring and turn it
over. Check for "rocking" motion.
3) Insert the cap screws and leaf spring
into the plastic housing.
4) Insert clamp assembly through the
heat sinks. Install the nuts. Tighten
the clamp nuts equally on the cap
screws until finger tight. (See Figure
F.29.)
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