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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.
CAUTION
LN-742 & LN-742H
PROBLEMS
(SYMPTOMS)
POSSIBLE AREAS OF
MISADJUSTMENTS(S)
RECOMMENDED
COURSE OF ACTION
F-7
TROUBLESHOOTING AND REPAIR
F-7
Observe all Safety Guidelines detailed throughout this manual
FUNCTION PROBLEMS (Continued)
The purge key does not activate the
gas solenoid. The solenoid does
activate when the gun trigger is
pulled.
The gas solenoid does not activate
either when the purge key is
pressed or when the gun trigger is
pulled.
The cold inch key does not activate
the wire feed motor. The wire feed
motor operates normally when the
gun trigger is pulled.
The HI symbol appears on the dis-
play when the voltmeter function is
selected.
The Er symbol appears on the dis-
play.
The EXX appears on the display.
(XX is some number from 1 to 10.)
The EP symbol appears on the
display.
The uP symbol appears on the dis-
play. (Microprocessor RAM error.)
1.
Contact your local Lincoln
Authorized Field Service Facility.
1. Check plug J6, located on the
control board for loose or faulty
connections.
1.
Contact your local Lincoln
Authorized Field Service Facility.
1. If the arc voltage is greater than
44 VDC, this is a normal condi-
tion. The voltmeter only reads
0-44 VDC.
1. This is an EPROM error. The
parameter recalled at power-up
is out of range. Press any key to
reset unit. Check all weld set-
tings before proceeding with
weld.
1. Remove input power to the feed-
er (42 VAC). Wait 5 seconds.
The symbol should not reappear
when power is returned.
1. Remove input power to the feed-
er (42 VAC). Wait 5 seconds.
The symbol should not reappear
when power is returned.
1. Remove input power to the feed-
er (42 VAC). Wait 5 seconds.
The symbol should not reappear
when power is returned.
1. Perform the
Keypad Resistance
Test.
2. The display board may be faulty.
1. With the Purge key pressed,
check for approximately 12 VDC
from 2J6 (+) to 1J6 (-). If the cor-
rect voltage is present, the sole-
noid may be faulty. If the 12 VDC
is low or missing, the Control
Board may be faulty.
1. Perform the
Keypad Resistance
Test.
2. The display board may be faulty.
1. The display board may be faulty.
2. The control board may be faulty.
1. If this condition persists, the con-
trol board may be faulty.
Replace.
1. If the EXX symbol reappears, the
control board may be faulty.
1. If the EP symbol reappears, the
EPROM may be faulty. Replace.
2. The control board may be faulty.
1. If the uP symbol reappears, the
control board may be faulty.
