Lincoln Electric IDEALARC CV-300 Service Manual page 77

F-38
SCR REMOVAL AND REPLACEMENT (CONTINUED)
PROCEDURE:
Note: Before disassembling the exist-
ing rectifier, note which heat sink the
outer metal ring of the power SCR is
mounted towards. Also, note the posi-
tioning 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 components of the
welder. See Figure 20.
GATE
ANODE
Fig. F.20 -SCR
The unclamping and clamping proce-
dure 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
HARDWARE, LEAF SPRING AND
HOUSING
REASSEMBLY.
2. Remove the old SCR.
TROUBLESHOOTING & REPAIR
CATHODE
OUTER METAL
RING
CAUTION
THAT NEW
BE USED
IDEALARC CV-300
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 mounting surfaces.
6. Apply a thin (0.001" to 0.003") layer
of PENETROX 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 material 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 facing
towards 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.
FOR
F-38