Lincoln Electric SVM127-A service manual Figure E.3 Trigger and Shutdown Circuit

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E-3 E-3

THEORY OF OPERATION

FIGURE E.3 – TRIGGER AND SHUTDOWN CIRCUIT

VOLTAGE CONTROL

							WORK VOLTAGE SENSING
					GEAR		ELECTRODE VOLTAGE SENSING		POLARITY
					BOX				SWITCH
									WIRE
					WIRE				SPEED
									CONTROL
					FEED
					MOTOR	TACH
						BOARD
	POWER SOURCE OUTPUT TRIGGER			(#2 )
							WIRE SPEED CONTROL
			TRIGGER		T2		+ 15VDC
	CIRCUIT	TRIGGER	BOARD
		CONNECTOR						C
	BREAKER			24VAC
								O	B
							TRIGGER SIGNAL
INPUT								N	O
					F
					U			T	A
CONNECTOR					S				R
					E			R
	R1						+ 15VDC		D
					P	B		O
					O
						O		L
					W	A
							S
					E	R
							H
					R	D	U
							T
TO							D
							O
CONTROL							W
BOARD							N
	T1						R	V
							E	O
							F
TO								L
							E
								T
VOLTAGE							R
							E	A
BOARD							N	G
							C	E
METER							E
	10VAC	28VAC
BOARD
					WIRE FEED				VOLTAGE
									CONTROL
					MOTOR
VOLTS					THERMOSTAT
SPEED
SWITCH								VOLTAGE
								BOARD

TRIGGER SIGNAL

GROUND

LEAD

PROTECTOR

TRIGGER AND SHUTDOWN

CIRCUIT

Return

Return

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 may also be used to energize a gas solenoid.

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 contacts would "open," and the trigger signal path would be interrupt- ed. This would cause the wire feeder to "shut down" until the gun trigger is released or the ground fault pro- tector is reset.

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

LN-9 Wire Feeder