Lincoln Electric IDEALARC CV-305 - Manual (Page 78)

SCR REMOVAL AND REPLACEMENT PROCEDURE
(CONTINUED)
TROUBLESHOOTING & REPAIR F-46 F-46
IDEALARC® CV-305
PROCEDURE:
Note: Before disassembling the existing rectifier, note
which heat sink the outer metal ring of the power SCR
is mounted towards. Also, note the positioning of the
gate lead of the SCR. Failure to reinstall the new SCR
in the same orientation as the original may result in
subsequent damage to the new SCR and other com-
ponents of the welder. See
Figure F.22.
Figure F.16 - SCR
The unclamping and clamping procedure outlined
below is critical for the prevention of internal SCR
damage. Failure to follow this procedure may
result in subsequent damage of the SCR. Handle all
SCRs with care.
____________________________________
1. Alternately loosen nuts 1/2 turn each until heat
sinks are loose. Remove nuts and leaf spring. IT
IS RECOMMENDED THAT NEW HARDWARE,
LEAF SPRING AND HOUSING BE USED FOR
REASSEMBLY.
2. Remove the old SCR.
3. Clean the area on the heat sink around the SCR
mounting surface. Using a putty knife, or similar
tool. DO NOT SCRATCH THE SCR MOUNTING
SURFACE.
4. Polish each heat sink's mounting surface using
NO. 000 fine steel wool. Wipe surface clean with
a lint free cloth or paper towel.
5. Inspect the mounting surfaces of each new
SCR.
a. Remove all burrs and wipe clean. Do not
use steel wool or any abrasive cleanser on
the SCR surfaces.
6. Apply a thin (0.001" to 0.003") layer of PEN-
ETROX A-13 (L.E. CO. #E2529) or PENETROX
A, heat sink compound, to each heat sink's SCR
mounting surface.
a. Care must be used to prevent foreign mate-
rial contamination of the SCR to heat sink
junction.
7. Place the new SCR between the heat sinks. Be
sure that the outer metal ring of the SCR is fac-
ing towards the same heat sink as the old SCR's
metal ring. Be sure that the emboss/indent of
the heat sink engages the "hole" in the SCR. The
SCR contact surfaces must sit flat against both
heat sink surfaces.
OUTER METAL
RING
ANODE
GATE
CATHODE
CAUTION
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