Troubleshooting & repair, Scr removal and replacement (continued), Caution – Lincoln Electric IDEALARC R3R-500 User Manual
Page 81
TROUBLESHOOTING & REPAIR
F-47
F-47
IDEALARC R3R
FIGURE F.28 – SCR DETAILS
SCR REMOVAL AND REPLACEMENT (continued)
SPECIAL INSTRUCTIONS
NOTE: Before disassembling the existing recti-
fier, note toward which heat sink the outer metal
ring of the power SCR is mounted. Also, note
the positioning of the gate lead of the SCR.
Failure to reinstall the new SCR in the same ori-
entation as the original may result in subsequent
damage to the new SCR and other components
of the welder. See Figure F.28.
The unclamping and clamping procedure out-
lined below is critical for the prevention of inter-
nal SCR damage. Failure to follow this proce-
dure may result in subsequent damage of the
SCR. Handle all SCRs with care.
PROCEDURE
1.
Remove the main input supply power to the
machine.
2.
Perform the SCR/Diode Rectifier Assem-
bly Removal procedure.
3.
Using the 7/16” wrench, remove the NEGA-
TIVE heat sink plate. Diode D4 pigtail will
have to be removed from the positive heat
sink plate. This will give access to the SCR
clamping hardware. When reassembling, be
sure all insulators are in place. The heat sink
plate should be electrically insulated from
the mounting thru-bolts.
4. 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.
5. Remove the old SCR.
6. 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.
7. Polish each heat sink’s mounting surface
using NO. 000 fine steel wool. Wipe surface
clean with a lint-free cloth or paper towel.
8. 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 mounting surfaces.
9. Apply a thin (0.001” to 0.003”) layer of PEN-
ETROX A-13 (Lincoln Electric #E2529) or
PENETROX A, heat sink compound, to each
heat sink’s SCR mounting surface.
a.
Care must be used to prevent foreign
material contamination of the SCR to
heat sink junction.
10. Place the new SCR between 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 surfaces must sit flat
against both heat sink surfaces.
CAUTION