Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 144

F-92
SCR REMOVAL AND REPLACEMENT (continued)
FIGURE F.31 – SCR CLAMP ASSEMBLY DETAILS - 5/8" WIDE SPRING
Cap Screw
Leaf Spring
Heat Sink
Plain Washer
Clamp Nut
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 the first cap screw 1/2 turn.
e. Tighten the second cap screw 1/4 turn.
f. Tighten the first cap screw 1/8 turn.
g. Tighten the second cap screw 1/8 turn.
Stop. The assembly now has the proper
clamping force.
TROUBLESHOOTING AND REPAIR
SCR
SQUARE WAVE TIG 355
Steel Pressure Pad
Plastic Housing
Heat Sink
8) Perform the Active SCR Test.
10. Install the output rectifier heat sink assembly
back into the machine. See Output Rectifier
Removal and Replacement in this section of
the manual.
F-92