Troubleshooting Guide - Lincoln LN-742 Service Manual

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TROUBLESHOOTING AND REPAIR

TROUBLESHOOTING GUIDE

Observe all Safety Guidelines detailed throughout this manual
PROBLEMS
(SYMPTOMS)
The display is blank. No wire feed
when the gun trigger is activated.
No wire feed when the gun trigger is
activated. The solenoid does not
function. No arc voltage present.
The display board indicates the LN-
742 has input power applied.
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you proceed. Call 216-383-2531 or 1-800-833-9353.
POSSIBLE AREAS OF
)
MISADJUSTMENTS(S
FUNCTION PROBLEMS
1. Make sure the control cable is
connected to the welding power
source correctly.
2. Make sure the welding power
source is turned on and function-
ing properly.
3. Check the 42 VAC fuse or circuit
breaker in the welding power
source.
1. Check or replace the gun trigger
switch.
2. Check the gun trigger recepta-
cle. Check for loose or faulty
connections.
CAUTION
LN-742 & LN-742H
RECOMMENDED
COURSE OF ACTION
1. Check for opens or shorts in the
control cable.
2. Perform the Input Voltage Test.
3. Perform the Drive Motor Test.
4. Observe LED 1 located on the
control board. It should blink on
and off at a controlled rate of 1
second on and 1 second off. If it
does NOT the control board may
be faulty. If LED does function
properly the display board may be
faulty.
1. Check the leads between the gun
trigger receptacle (J14) and plug
J1 located on the control board.
See wiring diagram.
2. The control board may be faulty.
Replace.
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