Trigger And Shutdown Circuit - Lincoln Electric SVM138-A Service Manual

E-3
CIRCUIT
BREAKER
INPUT
CONNECTOR
TO
CONTROL
BOARD
T1
TO
VOLTAGE
BOARD
METER
10VAC
BOARD
VOLTS
SPEED
SWITCH
TRIGGER AND SHUTDOWN
CIRCUIT
When the gun trigger switch is activated (closed), the
trigger board completes the trigger signal path. This
energizes the CR1 relay located on the power board.
The CR1 relay activates the wire drive motor and the
#2 and #4 circuit, which then activates the Lincoln
welding power source. The CR1 relay is also used to
energize the gas solenoid.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
THEORY OF OPERATION
FIGURE E.3 – TRIGGER AND SHUTDOWN CIRCUIT
GEAR
BOX
WIRE
FEED
MOTOR
POWER SOURCE OUTPUT TRIGGER (#2 &#4)
TRIGGER
T2
BOARD
TRIGGER
CONNECTOR
24VAC
R1
28VAC
LN-9 GMA Wire Feeder
WORK VOLTAGE SENSING
ELECTRODE VOLTAGE SENSING
HALL EFFECT
DEVICE
WIRE SPEED CONTROL
+ 15VDC
GAS
SOLENOID
TRIGGER SIGNAL
F
U
S
E
+ 15VDC
P
B
O
O
W A
S
E R
H
D U
R
T
D
O
W
N
TRIGGER SIGNAL
The normally closed relay located on the voltage
board is in series with the trigger signal. If an out-of-
voltage-range signal or a ground fault condition
should occur, the CR501 (on voltage board) relay con-
tacts would "open," and the trigger signal path would
be interrupted. This would cause the wire feeder to
"shut down" until the gun trigger is released or the
ground fault protector is reset.
VOLTAGE CONTROL
POLARITY
SWITCH
WIRE
SPEED
CONTROL
C
O
B
O
N
A
T
R
R
D
O
L
R
V
E
O
F
L
E
T
R
A
E
G
N
C E
E
VOLTAGE
CONTROL
VOLTAGE
BOARD
GROUND
LEAD
PROTECTOR
E-3