Lincoln Electric MULTI-WELD SVM151-A Service Manual page 68

F-28
CHOPPER PC BOARD INPUT VOLTAGES AND
Test Procedure for the Left Side
Power Module
1. Locate the Power Module Capacitor termi-
nals. Using the 7/16" wrench, disconnect
leads #X1, #X4, #401, #401A and the cop-
per straps.
these leads and straps from the capacitor
terminals and heat sink assembly.
Figure F.6.
2. Using the 3/8" nut driver, remove the four
screws holding the case back to the tunnel
assembly. This will provide access to the
IGBT heat sinks.
3. Using the analog ohmmeter, connect the
positive meter probe to the positive copper
strap and the negative meter probe to the
IGBT heat sink.
sink.) See Figure F.6 for test point loca-
tions. The resistance should be very high
(over 20,000 ohms). If the resistance is
low, then either the IGBT is shorted or the
diode D5 is shorted. Disconnect the small
D5 cathode lead to isolate the problem. It
is possible that both devices may be faulty.
4. Reverse the meter leads. The resistance
should be low (approximately 100 ohms). If
the resistance is high, the diode D5 may be
open.
5. Using the analog ohmmeter, check diode
module D3. Connect the negative meter
probe to the negative copper strap connect-
ed to the diode module and the positive
probe to the heat sink. See Figure F.6 for
the test point locations.
should be very high (over 20,000 ohms). If
the resistance is low, the diode module D3
may be shorted.
6. Reverse the meter leads. The resistance
should be low (approximately 100 ohms). If
the resistance is high, the diode module D3
may be open.
7. Repeat Steps 1 through 5 for the Right
Side Power Module.
Diagram.
8. Replace all leads previously removed. See
Figure F.6 and the Wiring Diagram. Torque
the capacitor bolts to 50 to 60 inch pounds.
TROUBLESHOOTING & REPAIR
RESISTANCE TEST (CONTINUED)
Carefully electrically isolate
(This is the inner heat
The resistance
See the Wiring
MULTI-WELD 350
CHOPPER PC BOARD VOLTAGE
TESTS FOR BOTH LEFT AND
RIGHT SIDES
1. Locate Plug P45(A) and disconnect it from
J45(A). See Figure F.6.
See WARNING
ELECTRIC SHOCK can kill.
With the input power ON, there are high volt-
ages inside the machine. Do not reach into the
machine or touch any internal part of the
machine while power is on.
2. Carefully apply the correct input voltage to
the Multi-Weld 350 (50 – 113 VDC). The
machine should be in the CC mode and the
CC Slope switch should be in the
Stick/Gouge position.
3. Turn the machine on and carefully check for
18.0 – 21.0 VDC at P45(A) pin 1 (+) to
P45(A) pin 3 (-). This is the 20 VDC supply
from the Analog Control Power Supply PC
Board to the Chopper PC Board.
NOTE: Be careful not to touch the capacitor
terminals.
4. Also carefully check for 11.0 – 14.0 VDC at
P45(A) pin 7 (+) to P45(A) pin 9 (-). This is
the Pulse Width Modulation Signal from the
Weld Control Board to the Chopper PC
board.
5. If any of the voltages are not present, check
associated leads and plugs for loose or
faulty connections.
Diagram.
6. Remove the input power and perform the
Power Module Capacitor Discharge
Procedure.
7. Reconnect the plugs previously discon-
nected.
8. If finished testing, perform the Case Cover
Replacement procedure.
F-28
See the Wiring