Theory Of Operation; General Description; Input Power Circuits - Lincoln LT-7 Troubleshooting Manual

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GENERAL DESCRIPTION

The LT-7 tractor is a compact, lightweight, DC, single arc tractor. It is capable of operating with 3/32" through
3/16" electrode with a current carrying capacity of 1000 amps. The LT-7 has a travel range from 6 to 70 inches
per minute.
TRAVEL
SPEED
CONTROL
115VAC
CIRCUIT
FROM
BREAKER
WELDING
115VAC
POWER
SOURCE
115VAC
115VAC

INPUT POWER CIRCUITS

The LT7 is powered by 115VAC which is usually sup-
plied from the welding power source. The 115VAC is
applied to the travel board. This voltage is also coupled
to the control box circuitry through the on/off power
switch and a 3 amp circuit breaker. The input power is
then applied to the the variable voltage board and,
through resistor R1, to the control board. The 115VAC
is rectified and regulated by the control board which
supplies 24VDC to the logic board.
NOTE: Unshaded areas of the Block Logic Diagram are the subject of discussion

THEORY OF OPERATION

DIRECTION
TRAVEL BOARD
115VAC
INCH UP
SWITCH
1CR
POWER SOURCE
CONTACT RELAY
#2
#4
R1
CONTROL
115VAC
VARIABLE VOLTAGE
BOARD
115VAC
{
ELECTRODE
VOLTAGE
SENSING
LEADS WORK
FIGURE E.1 - 115VAC INPUT POWER CIRCUITS
LT-7 TRACTOR
TRAVEL
SWITCH
TRAVEL
CONTROL
SWITCH
WIRE
DRIVE
MOTOR
BOARD
LOGIC CONTROL SIGNALS
24VDC
ARC VOLTAGE SENSING SIGNALS
START
SWITCH
STOP
SWITCH
INCH
DOWN
SWITCH
ARC
VOLTAGE
METER
TRAVEL
MOTOR
2CR
TRAVEL
RELAY
115VAC
GLP WELD CURRENT
REED SENSING REED
SWITCH 3CR
SWITCH 4CR
LOGIC
BOARD
WIRE
SPEED
CONTROL
115VAC
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