ELECTRICAL DIAGRAMS G-8
LF-72/74

SCHEMATIC - ENTIRE MACHINE - CODE 11290, 11291, 11292,11293 (G4617-2) LF-72

A
D
C
B
E
554
556
TRIGGER
CONNECTOR
J13
559
515
558
COLD FEED
S1
FEED
PLATE
TRIGGER
INPUT
67
556
J1-4
J1-5 J1-11
J1-12
J1-15
559
1
4
3
2
6
5
P10
8
7
MOTOR /
GEARBOX
W
B
L5
515
558 589
587
554
A
550
551
550
576
577
575C
553
552
2
4KEY
580
552A 605
606
601
607
608
515A
THERMAL LED
1W
563
562
575B
562
1B
1W
1B
10K/2W
2
1
P7
4
3
REMOTE
CONTROL
VOLTAGE
POTENTIOMETER
(OPTIONAL)
75A
76A
77A
WIRE FEED
SPEED
CONTROL
POTENTIOMETER
10K/2W
589
TRIGGER
INTERLOCK
S2
587
-
+
580 42
552A
41
552B
TIMERKIT
(OPTIONAL)
SCHEMATIC=
M20336
J60-6
601
515A
605 607
608
606A
552
553
GAS
SOLENOID
OUTPUT
CONTROL
J12
2
C
4
D
77A
E
76A
F
75AG
41
I
J
42
K
L
M
67
N
REMOTE
VOLTAGE
CONTROL
SENSE
552B
2-STEP
GASPURGE
L1
577
576
575
75
76
77
L2
L3
575
575C
575B
24-42VAC
L4
562
563
15 VDCin
2STEP
position
5VDC
when lit
38VDC at
42VAC input
with control
board
disconnected.
60VDC with
control board
connected
1.6V @ 100IPM
30.6V @ 800IPM
Motoris located
behind
glasticpanel
Lightswhenmotor
current exceeds3.75Amps foran
extended time.
Off= 0 VDC
OCV = 59 VDC
On= 7.7 VDC
Locatedon
CaseFront
Locatedon
CaseFront
Locatedon
CaseFront
Locatedon
case back
Values forCV305. Others
may be different.
0VDC @ 0 = 5.8 Arc Volts
6.6 VDC @ 10 = 40 ArcVolts
0VDC MIN. WFS
5VDC MIN. WFS
Trigger Interlock does not
stopweldingwhen the
arc is broken. Pulland
release to end theweld.
15 VDC Open
0VDC Closed
15 VDC Open
0VDC Closed
Gearbox ratio is2:47
Motoris atelectrode
potential
Start-Up
On power-up, the LF-72 will light themotorthermal LED for 0.5 seconds.If the feederis powered-up with the triggerdepressed, welding will not start until thetrigger is released and then depressedagain.

Notes

TheWFS range of the LF-72 is 50-800ipm.To Power Source ElectrodeConnection
750ohm +15V
750ohm TRIGGER
OPEN = 0V
CLOSED = 8V
MOTOR
CURRENT
SENSE
SCALING
MOTOR
VOLTAGE
SENSE
BRAKE
FET
DRIVE
FET
0.1ohm
MOTOR
DRIVE
CIRCUIT
+POWER
J1-1
+5V
FILTER TACH
FEEDBACK
0-5V PULSE SIGNAL
FREQUENCY = SPEED
J1-9
J1-13J1-3
100K
ohm
WIRE
FEED
SPEED
0V = MIN SPEED
5V = MAX SPEED
+5V
J1-8
200 ohm GAS
SOLENOID
SOLENOID
FET
10K
ohm
0.25
ohm
J1-2 J1-6J1-16
+POWER
COM
COM
BOARD
POWER
SUPPLY
J14-1J14-9
MOV
20
ohm
MACHINE
OUTPUT
ENABLE
J14-8 J14-14 J14-2J14-5
+5V
BURNBACK
0V = 0.02 SECONDS
5V = 0.25 SECONDS
J14-4
EXTERNAL
GAS
SOLENOID
CONTROL
LOW = CONTROL AT CONTROL BOARD
HIGH = CONTROL ATTIMER BOARD
J14-12 J14-13
PROGRAM
DO NOT USE
NOT FIELD PROGRAMMABLE
J14-7
200ohm
THERMAL
LED
5V = OFF
4V OR LESS = ON
J14-10
COLD
FEED
LOW = DISABLE
HIGH = ENABLE
J14-16 J14-11J14-15 J14-3
GAS
PURGE
LOW = DISABLE
HIGH = ENABLE
+15V +15V
TRIGGER
INTERLOCK
LOW = DISABLE
HIGH = ENABLE
+15V
MICRO
CONTROLLER
COMMON ANALOG P.C. BOARD
SCHEMATIC= G4559
ControlBoard Summar
y
•Hason-board power supply.
•Receivesswitch signals fr om Trigger, Cold Feed, Gas Purge, Trigger
Interlock
•ReadsWFS potentiometer.
•Communicateswith optional timerkit tocontrol burnback, postflow.
•Controlsmotor speed withPWM.
•TurnsGas Solenoid on,off.
•Readsthe motortachometer.
•Monitorsmotor current,lights yellowthermal LEDif over 3.75 amps for an
extendedtime period. LED remains litfor 30 –60 seconds toallow motor
tocool.
•DoesNOT supportRun-in at thistime.
•Operateson 24-42 VAC. MaximumWFS and/or maximum pullforce may
be lesswhen operating at24 VAC.
•DoesNOT operate on 115VAC.
J60-5J60-8 J60-7 J60-1J60-3
+15V
COM
COM
BURNBACK
POT
PREFLOW &
POSTFLOWTIMER
LOGIC
POSTFLOW
POT.
Ab
PREFLOW
TIME FIXED
AT 30msec
cD
POSTFLOW
TIME RANGE
.25 - 10 SEC
FIXED
PULSE
WIDTH
GENERATOR
Ac
5VSIGNAL
GAS FLOW
ENABLE
LocatedonCase Front
INPUT
OUTPUT
b15V SIGNAL
100 msec PULSES
TOGGLE GAS FLOW ON/OFF
DTime
r
BoardSummar
y
•Haspotentiometers for burnbackand postflow.
•Preflowfixed at 30msec.
•Burnbackrange is 0to 0.25 sec.
•Postflowrange is0.25 to10 sec.
•Receives“Gas FlowEnable” signal.
•Outputs 100msec pulses toturn GasFlow On, Gas
FlowOff.
J2-1J2-2 J2-3 J2-4 J2-5 J2-6 J3-1 J3-2
NOT USED
NOT USED
Connectorlocated
by sheetpanel Motor resistance
is 1.5 ohms
Connectorlocated
behindcase front
LeadsPass through
toroid 2 times.
Coil
measures
21 ohms
INDEX
MOLEX
+5V +15V
R
U
B
4
3
2
14
32
1
4
32
1
A
B
521
522
P4
P11
P6
521
522
551B
L6
551
Locatedon
CaseFront
Locatedon
CaseFront
Locatedon
CaseFront
Locatedon
CaseBack
Locatedon
SheetPanelLeadsPass
through
toroid 2
times.
LeadsPass through
toroid 3 times.
LeadsPass
through
toroid 2 times.
551A
LeadsPass
through
toroid 2
times.
Connectorlocated
behindsheet panel
MotorConnecte
r
Summar
y
•P6not used – required for LF-74
only..
20 OHM = OUTPUT ENABLED
HIGH IMPEDANCE = OUTPUTDISABLED
LeadsPass
through
toroid 2
times.
563
Connectorlocated
on sheetpanel

G-8

NOTE: This diagram is for reference only.It may not be accurate for all machines covered by this manual.
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