Lincoln Electric SVM138-A service manual Theory of Operation, Figure E.2 Power Input Circuits

E-2 E-2

THEORY OF OPERATION

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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, 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.

FIGURE E.2 – POWER INPUT CIRCUITS

VOLTAGE CONTROL

WORK VOLTAGE SENSING

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GEAR		ELECTRODE VOLTAGE SENSING
BOX
WIRE
FEED
MOTOR	HALL	EFFECT
	DEVICE

POWER SOURCE OUTPUT TRIGGER (#2 )

					WIRE SPEED CONTROL
					+ 15VDC
		TRIGGER	T2
	TRIGGER	BOARD			GAS
CIRCUIT
	CONNECTOR				SOLENOID
BREAKER		24VAC
INPUT					TRIGGER SIGNAL
			F
			U
CONNECTOR			S
			E
R1			P	B	+ 15VDC
			O	O
			W	A	S
			E	R
					H
			R	D	U
					T

TO		D
		O
CONTROL		W
BOARD		N
		T1
TO
VOLTAGE
BOARD
METER	10VAC	28VAC
BOARD
VOLTS
SPEED
SWITCH

POLARITY

SWITCH

WIRE

SPEED

CONTROL

C

OB

NO

TA

RR

D

O

L

RV E O F

E L R T E A N G C E

E

VOLTAGE

CONTROL

VOLTAGE

BOARD

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TRIGGER SIGNAL

GROUND

LEAD

PROTECTOR

POWER INPUT CIRCUITS

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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.

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.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

LN-9 GMA Wire Feeder