Troubleshooting & repair – Lincoln Electric MULTI-WELD SVM151-A User Manual
Page 96
TROUBLESHOOTING & REPAIR
F-56
F-56
MULTI-WELD 350
CHOPPER PC BOARD REMOVAL AND REPLACEMENT (CONTINUED)
3. Perform the Case Cover Removal proce-
dure.
4. Perform the Power Capacitor Discharge
procedure.
5. Carefully turn the machine onto its side.
6. Using the 3/8" wrench, remove the four
screws holding the tunnel assembly to the
machine base. Support the tunnel assem-
bly, then carefully turn the machine back
upright.
7. With the slot head screw driver, carefully
raise the tunnel assembly unit about one
inch and block it with the piece of wood.
This will allow access to the bottom allen
head screws on the Chopper PC Board.
Peel away the adhesive-backed rubber
stripping if present. Use care – the strip-
ping may tear.
8. Disconnect the plug harness connection
above the Chopper PC Board. Slip the
wires out of the cord clip.
9. Using the 7/16" wrench, loosen the bolt at
the positive capacitor terminal. Then
remove the two nuts, lock washers and flat
washers holding the positive strap to the
Chopper PC Board. Hold the screw heads
behind the board with your finger to
remove the nuts. Note the placement of
the reverse diode lead on the bottom bolt.
Note the fastener order for reassembly: flat
washer, lock washer, nut.
10. With the 7/16" wrench, remove the two
hex-head bolts, lock washers, and flat
washers holding the Chopper PC Board to
the heat sink. Catch the copper stand-offs
behind the board.
11. Using the 3/16" allen head wrench, remove
the two allen-head screws and lock wash-
ers holding the Chopper PC Board to the
heat sink.
12. Swing the positive capacitor strap out of
the way and remove the Chopper PC
Board.
REPLACEMENT
1.
Make sure the mating surfaces between the
copper and the heat sink are clean, dry, and
free of grease.
2.
Apply a thin coating of electrical thermal
joint compound (Penetrox A-13) to the mat-
ing surfaces between the copper and the
aluminum heat sink.
3.
Using the torque wrench and 3/16" allen
head socket, install the two allen-head
screws and lock washers that hold the
Chopper PC Board to the heat sink.
Tighten the screws finger tight, then to
between 24 and 28 in-lbs., then again to
between 40 and 48 in-lbs.
4.
Using the 7/16" socket and torque wrench,
install the two bolts, lock washers, and flat
washers that hold the Chopper PC Board to
the heat sink. Note the two spacers
required. Tighten the bolts finger tight, then
to between 50 and 60 in-lbs.
5.
Put the positive strap (+) in position and the
proper heavy lead. Using the 7/16" wrench,
tighten the bolt at the positive capacitor ter-
minal to between 50 and 60 in-lbs. Then
put the flat washers, lock washers and nuts
on the board side of the strap with the
reverse diode lead on the bottom connec-
tion. Tighten to between 50 and 60 in-lbs.
6.
Remove the wooden blocking and carefully
lower the tunnel assembly onto the
machine base. Support the tunnel assem-
bly and turn the machine onto its side.
7.
With the 3/8" wrench, install the four screws
that hold the tunnel assembly to the
machine base. Turn the machine back
upright.
8.
Connect the harness plug above the
Chopper PC board. Slip the wires into the
cord clip.
See the procedures following for removal and
replacement of the diode module. When proce-
dures are complete, perform the Case Cover
Assembly Replacement procedure.