Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 142

F-90
SCR REMOVAL AND REPLACEMENT (continued)
FIGURE F.29 – SCR CLAMP ASSEMBLY DETAILS - 1/2" WIDE SPRING
Cap Screw
Plain Washer
5) Re-inspect the SCR for proper seating.
6) Clamp the cap screws. Use the procedure
for 1/4-28 cap screws or 1/4-20 bolts,
depending on which you have.
Clamping procedure for 1/4-28 cap screws.
NOTE: This procedure can only be used with
1/4-28 bolts. Do not use bolts 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 bolts only with the fol-
lowing 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 1/4 turn. Stop. The
assembly now has proper clamping force.
TROUBLESHOOTING AND REPAIR
Leaf Spring
SCR
Heat Sink
Clamp Nut
SQUARE WAVE TIG 355
Plastic Housing
Heat Sink
Clamping procedure for 1/4-20 cap screws.
NOTE: This procedure can only be used with
1/4-20 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 1/4 turn. Stop.
The assembly now has the proper clamping
force.
7) Perform the Active SCR Test.
F-90