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F-80 F-80
SCR REMOVAL AND AND REPLACEMENT (continued)
TROUBLESHOOTING & REPAIR
8. Place the new SCR betwen the heat sinks.
Be sure that the outer metal ring of the
SCR is facing 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 sur-
faces 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
housings have been used to clamp the
SCR to the rectifier. The two different
designs can be identified 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
assembly and clamping procedures,
depending upon the thread on the cap
screws. A 1/4-28 thread requires a differ-
ent tightening procedure than a 1/4-20
thread. NOTE WHICH THREAD IS ON
YOUR CAP SCREWS BEFORE PER-
FORMING THE ASSEMBLY PROCEDURE.
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.)
SQUARE WAVE TIG 355
FIGURE F.28 – 1/2” WIDE LEAF SPRING
Spring curvature exaggerated