General Description; Power Input Circuits; Theory Of Operation - Lincoln LN-742 Service Manual

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GENERAL DESCRIPTION

The LN-742 is a semiautomatic constant
speed wire feeder with a gas solenid valve
and fittings. It also has standard Lincoln gun
connector. An LED display and a soft touch
keypad provide selection of operating mode,
function selection, timer selection, and
parameter adjustment.
operate the cold-inch and gas purge
functions.
42VAC
42VAC
INPUT CABLE
RECEPTACLE

THEORY OF OPERATION

Two touch keys
FIGURE E.1 – POWER INPUT CIRCUITS.
KEYPAD
AC DC+
CONTROL BOARD
AC DC-
CONTACTOR CONTROL
LN-742 & LN-742H

POWER INPUT CIRCUITS

The LN-742 receives 42 VAC (usually from
the welding power source) by way of the
input cable connector.
rectified to a DC voltage and applied to the
control board. The control board regulates
the rectified voltage to a +12.8 VDC supply
and also +5 VDC supply. A variable 0 to 23
VDC is also applied to the wire drive motor
via the control board.
DISPLAY
PC BOARD
FEEDBACK
GAS GUN TRIGGER
SOLENOID RECEPTACLE
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The 42 VAC is
CURRENT
SENSING
REED
SWITCH
DRIVE
MOTOR
TACH