Lincoln Electric SVM170-A service manual Output Rectification, Feedback Control

E-3 THEORY OF OPERATION E-3

TOC	TOC	FIGURE E.3 — OUTPUT RECTIFICATION AND FEEDBACK.
Section	Master		GAS	FAN	SPOOL
			SOLENOID	MOTOR			WIRE
						GUN
							DRIVE
		WIRE					MOTOR
to	to
		SPEED
Return	Return	ARC	CONTROL
		VOLTAGE	BOARD
		AUX					TACH
		115 VAC						GUN TRIGGER
			RECTIFIER
			DIODE	G				FEEDBACK
			BRIDGE
				A
		30 VAC		T
				E
		LINE	SNUBBER	S
			BOARD
		SWITCH		I
				G
				N
TOC				A
	TOC			L
Section	Master			POWER		C	F	OUTPUT	POSITIVE
		RECONNECT		ENHANCEMENT		A		CHOKE
									TERMINAL
		MAIN		CHOKE		P	E
		TRANSFORMER				A	E
			SCR			C	D
to	to						B
			RECTIFIER			I
						T	A
Return	Return
						O	C		NEGATIVE
						R	K
									TERMINAL
						S
						SHUNT

		OUTPUT RECTIFICATION AND	the commands of the ARC Voltage Control poten-
		FEEDBACK CONTROL	tiometer with the feedback signals. The appropriate
			gate firing pulses are generated by the control board
		The AC output from the main transformer secondary	and applied to the SCR rectifier assembly. The control
			board controls the firing of the SCRs, thus controlling
TOC	TOC	weld winding is rectified and controlled through the	the output of the machine. See SCR Operation. The
		SCR rectifier assembly. Output voltage and current are	control board also powers and commands the gas
SectiontoReturn	MastertoReturn	sensed at the shunt and output terminals and are fed	solenoid, fan motor, the wire drive motor, and spool
		back to the control board. The control board compares	gun receptacle.

Section TOC	Master TOC
to	to	NOTE: Unshaded areas of Block Logic
		Diagram are the subject of discussion
Return	Return
		POWER MIG 255C