Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 143

F-91
SCR REMOVAL AND REPLACEMENT (continued)
FIGURE F.30 – HOUSING AND PRESSURE PAD FOR 5/8" WIDE LEAF SPRING
B. PROCEDURE FOR THE 5/8 INCH WIDE
SPRING:
1) Place a piece of sleeving around each cap
screw.
2) Insert the cap screws through the leaf
spring. The leaf spring is flat so the orien-
tation of the leaf spring does not matter.
3) Place the steel pressure pad in the hous-
ing with the 1/8" wide standoff facing up.
See Figure F.30.
4) Insert the cap screws and leaf spring into
the plastic housing. Be sure that the steel
pressure pad
Pressing on the cap screw heads should
produce a rocking action of the spring in its
housing.
5) Insert the clamp assembly through the
heat sinks. Install the nuts. Tighten the
clamp nuts equally on the cap screws until
finger tight. Be sure that the leaf spring is
not cocked in the housing. See Figure
F.31.
6) Re-inspect the SCR for proper seating.
7) Clamp the cap screws. Use the procedure
for 1/4-28 cap screws or 1/4-20 cap
screws, depending on which you have.
TROUBLESHOOTING AND REPAIR
Steel Pressure Pad
Housing
remains in position.
SQUARE WAVE TIG 355
Clamping procedure for 1/4-28 cap screws.
NOTE: This procedure can only be used with 1/4-
28 cap screws. Do not use cap screws
with any other type thread, or the new SCR
will be damaged. Do not overtighten the
cap screws. The leaf spring will apply the
required clamping force to the SCR.
a. Do not turn the nuts. While holding the
nuts stationary, turn the cap screws only
with the following procedure.
b. Tighten first cap screw 1/4 turn.
c. Tighten second cap screw 1/2 turn.
d. Tighten first cap screw 1/2 turn.
e. Tighten second cap screw 1/2 turn.
f. Tighten first cap screw 1/2 turn.
g. Tighten second cap screw 1/4 turn. Stop.
The assembly now has the proper clamp-
ing force.
F-91