Filter
Top Products
FIGURE E.2
GENERAL DESCRIPTION & INPUT RECEPTACLE, CONTROL BOARD AND OPERATOR CONTROLS
14 PIN
INPUT CABLE
R
ECEPTACLE
2
4/42 VAC
CONTROL BOARD
WIRE FEED
SPEED POT.
TRIGGER
INTERLOCK
2-STEP
C
OLD FEED
GAS PURGE
OPTIONAL
BURNBACK
TIMER
OPTIONAL
REMOTE
VOLTAGE
C
ONTROL
GAS
SOLENOID
3.75 AMP
OVERLOAD
PROTECTION
WIRE DRIVE
RECEPTACLE
WIRE
DRIVE
MOTOR
TACK
To Gun Trigger
THEORY OF OPERATION
GENERAL DESCRIPTION
The LF72 and LF74 are single head, 24vac or 42vac
input, 2 roll (LF72) or 4 roll (LF74) wire feeders. They
have a single calibrated control for wire feed speed
WFS and an optional
K2339-1 remote voltage control
kit to be used in conjunction with a Lincoln constant
voltage (CV) direct current DC power source.
The LF72 and LF74 offer the user 3 individual features
Cold feed, trigger interlock 2 step trigger control and
gas purge. Presettable burnback and postflow timers
are also available with an optional
K2330-1 timer kit.
The motor is equipped with a 3.75amp current over-
draw protection circuit, which is indicated by a THER-
MAL LED located on the case front.
INPUT RECEPTACLE, CONTROL
BOARD AND OPERATOR CON-
TROLS
The 24 or 42-volt input is applied to the LF72 or LF74
through the 14 pin amphenol type connector. The
remote trigger leads are accessed through 14 pin
receptacle. The input voltage is rectified by a full wave
bridge and is sent to a switching power supply in the
control board where it is filtered. This filtered DC volt-
age is applied to a switching power supply. The
switching power supply manufactures +15vdc and
+5vdc regulated supplies for the control board circuit-
ry.
The control board receives commands from the user
operated controls for the wire feed speed WFS pot,
the optional timer kit and the optional voltage remote
control kit. It compares this feedback information with
the user command signals and generates appropriate
signals to control wire feed speed, arc voltage and gas
flow.
The control board is also responsible for the operation
of the trigger interlock, 2-step, cold feed and the gas
purge features of the LF72 and the LF74.
E-2 E-2
Return to Section TOC Return to Section TOC Return to Section TOC Return to Section TOC
Return to Master TOC Return to Master TOC Return to Master TOC Return to Master TOC
LF-72/74 SINGLE/DUAL