Theory Of Operation; General Description; Power Input Circuits - Lincoln Electric SVM138-A Service Manual

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GENERAL DESCRIPTION

The LN-9 GMA is a semiautomatic wire feeder that allows
the user to preset the arc voltage and wire feed speed.
The wire feed speed is internally monitored and
regulated to the preset condition. When the LN-9 GMA is
coupled to an appropriate Lincoln constant voltage
POWER SOURCE OUTPUT TRIGGER (#2 &#4)
CIRCUIT
BREAKER
INPUT
CONNECTOR
TO
CONTROL
BOARD
T1
TO
VOLTAGE
BOARD
METER
10VAC
BOARD
VOLTS
SPEED
SWITCH

POWER INPUT CIRCUITS

The 115VAC is applied (usually from the welding power
source) via the input connector and through the circuit
breaker and R1 resistor to the power board, the T2 trig-
ger transformer, and the T1 transformer.
The 24VAC developed at the T2 trigger transformer is
applied to the trigger board. There it is rectified and
regulated to 20VDC and used to operate the wire feed-
er trigger circuitry.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

THEORY OF OPERATION

FIGURE E.2 – POWER INPUT CIRCUITS
GEAR
BOX
WIRE
FEED
MOTOR
TRIGGER
T2
BOARD
TRIGGER
CONNECTOR
24VAC
F
U
S
E
R1
28VAC
LN-9 GMA Wire Feeder
power source, the actual arc voltage is also regulated to
match the preset voltage. The LN-9 GMA models also
incorporate a factory installed gas solenoid valve, high
speed wire drive, adjustable run-in and acceleration
speeds, and a two-step/four-step trigger interlock system.
WORK VOLTAGE SENSING
ELECTRODE VOLTAGE SENSING
HALL EFFECT
DEVICE
WIRE SPEED CONTROL
+ 15VDC
GAS
SOLENOID
TRIGGER SIGNAL
+ 15VDC
P
B
O
O
W
A
S
R
E
H
U
D
R
T
D
O
W
N
R
E
F
E
R
E
N
C
E
TRIGGER SIGNAL
The 28VAC produced by the T1 transformer secondary
is applied to the power board. There it is rectified and
regulated to 15VDC. This 15VDC powers the electron-
ics on the power, control, and voltage boards. The
10VAC secondary voltage is rectified, regulated, and
utilized by the meter board.
VOLTAGE CONTROL
POLARITY
SWITCH
WIRE
SPEED
CONTROL
C
O
B
N O
A
T
R
R
D
O
L
V
O
L
T
A
G
E
VOLTAGE
CONTROL
VOLTAGE
BOARD
GROUND
LEAD
PROTECTOR
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