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TEST PROCEDURE
1. Remove input power to wire feeder.
2. Remove electrode wire or disengage
drive rolls.
3. Using 5/16" nutdriver, remove the
screws from the left side cover
assembly.
4. Remove the left side cover assembly.
5. Locate plug J3 on the control board
shown in Figure F.1. Do not remove.
6. Apply input power to the wire feeder (42
VAC).
7. Check from the red lead (+) (1J3) to the
black lead (-) (3J3) for the presence of
+12.8 VDC. If this voltage is missing or
low, the control board may be faulty.
8. With the gun trigger activated, or the
gun trigger terminals jumpered together
(refer to
Section G, Electrical
Diagrams), and the motor running,
check from the blue lead (+) (2J3) to the
black lead (-) (3J3) for the presence of
approximately 1.5 VDC. Note: When
the motor is not running, the voltage
may be from 0 to 2.5 VDC. If this
feedback voltage is missing, the
tachometer assembly may be faulty.
Replace the tachometer.
9. Install the left side cover assembly
using screws and the 5/16" nutdriver.
(2J3)
BLUE
LEAD
PLUG
J3
(3J3)
BLACK
LEAD
(1J3)
RED
LEAD
LN-742 & LN-742H
F-11
TROUBLESHOOTING AND REPAIR
F-11
TACHOMETER FEEDBACK TEST
(continued)
FIGURE F.1 – TACHOMETER FEEDBACK TEST POINTS.