Control Logic And Travel Boards - Lincoln LT-7 Troubleshooting Manual

A-2
CONTROL
115VAC
CIRCUIT
FROM
WELDING BREAKER
115VAC
POWER
SOURCE
115VAC
115VAC
FIGURE E.2 - CONTROL LOGIC AND TRAVEL BOARDS
CONTROL, LOGIC AND TRAVEL
BOARDS
Upon receiving commands from the user operated
switches or potentiomenters the logic board sends the
appropriate signal to the control board which then dri-
ves the wire feed motor to the correct speed and direc-
tion. When the start signal is received by the control
board the power source contact relay(1CR) is ener-
gized as well as the travel relay(2CR) and the wire drive
motor. When weld current closes reed switch 3CR the
logic board directs the control board to change the wire
feed speed from the preset inch speed to the welding
feed speed set by the wire speed control potentiome-
ter. Reed switch 4CR protects the internal grounding
wire circuitry. In the event that abnormally high current
NOTE: Unshaded areas of the Block Logic Diagram are the subject of discussion
THEORY OF OPERATION
DIRECTION
TRAVEL
SPEED
TRAVEL BOARD
115VAC
1CR
POWER SOURCE
CONTACT RELAY
#2
#4
R1
115VAC
VARIABLE VOLTAGE
115VAC
{
ELECTRODE
VOLTAGE
SENSING
LEADS WORK
LT-7 TRACTOR
TRAVEL
SWITCH
CONTROL
SWITCH
INCH UP
SWITCH
WIRE
DRIVE
CONTROL
MOTOR
BOARD
LOGIC CONTROL SIGNALS
24VDC
ARC VOLTAGE SENSING SIGNALS
START
SWITCH
STOP
SWITCH
BOARD
INCH
DOWN
SWITCH
ARC
VOLTAGE
METER
was to flow in the grounding lead system the 4CR reed
switch would close, signaling the logic board to stop the
welding procedure. The inch up switch, which is cou-
pled directly to the control board, dictates that the wire
drive motor reverse direction and back the electrode
wire away from the work piece.
Travel speed, direction and mode (either manual or
auto) are determined by the settings of the three con-
trols connected to the travel board. The travel board
then applies the correct voltage and polarity to the trav-
el motor to satisfy the control settings.
TRAVEL
MOTOR
TRAVEL
2CR
TRAVEL
RELAY
115VAC
GLP WELD CURRENT
SENSING REED
REED
SWITCH 3CR
SWITCH 4CR
LOGIC
BOARD
WIRE
SPEED
CONTROL
A-2
115VAC