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POWER MIG 255
TROUBLESHOOTING & REPAIR
F-29 F-29
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2. Locate plug J1 on the G3521 control
PC board. See Figure F.9.
3. Locate the following leads on Plug J1:
4. Connect main input power to the
machine.
5. Make the following voltage tests:
a. Turn the machine OFF between
each test.
b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity.
6. If the 15 VDC is present, check the
leads to the tachometer circuit.
7. If the leads are okay and 15 VDC is
present, the correct voltage is being
received from the control PC board,
continue with the Supply Voltage to
Tachometer Test.
8. If the 15 VDC is not present and the
leads are okay, the control PC board
may be faulty, replace the control PC
board.
6. Make the following voltage tests:
a. Turn the machine OFF between
each test.
b. Carefully insert the meter probes
into the back of each Molex plug
pin cavity to perform the test.
c. Turn the machine ON and pull the
gun trigger to conduct the voltage
test.
7. If the voltage to the wire drive motor
armature is zero, check the wires
between plug J1 and the wire drive
motor. Also check the electrical connec-
tor J12 for proper connection and con-
tact.
8. If all wires and connectors are good and
the voltage to the drive motor armature
is zero, the G3521 control PC board
may be faulty, replace the control PC
board.
9. If the motor is running at high speed
and the armature voltage is high and
uncontrollable, proceed with the
tachometer test.
TEST FOR SUPPLY VOLTAGE
TO TACHOMETER
1. Disconnect the main AC input power to
the machine.
WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST (continued)
FROM
LEAD
B
(4J1)
TO
LEAD
W
(2J1)
EXPECTED
VOLTAGE
3-20 VDC
(varies depend-
ing on wire feed
speed)
FROM
LEAD
515B
(5J1)
TO
LEAD
206B
(1J1)
EXPECTED
VOLTAGE
15 VDC
PLUG
LOCATION
5J1
1J1
LEAD
515B
206B