Lincoln Electric DC-655 service manual Table of Contents Theory of Operation Section

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Section E-1Section E-1

TABLE OF CONTENTS

-THEORY OF OPERATION SECTION-

Theory of Operation	Section E
General Description	E-2
Input Line Voltage, Contactor, Reconnect,
Fault Protection, Main and Control Transformers	E-2
Control Board, Firing Board, Snubber/Fan
Board and Rectification	E-3
Protective Devices and Shutdown Circuits	E-4
Thermal Protection	E-4
Over Current Protection	E-4
Peak Current Protection	E-4
Remote Control Fault Protection	E-4
Shorted Output Rectifier Fault Protection	E-4
SCR Operation	E-5

FIGURE E.1 – DC-655 BLOCK LOGIC DIAGRAM

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CONTROL

TRANSFORMER

115VAC

CR2

R

E

C

O

N

N

E

C

T

CONTACTOR

CR1

42VAC

CONTROL

BOARD

TRANSFORMER

FAULT PROTECTION

							OUTPUT		ARC FORCE
							CONTROL
32VAC						OUTPUT			CONTROL
				FIRING		CONTROL SIGNAL
32VAC
32VAC				BOARD
				G	S
14-pin		115VAC	Fan	A	I
				T	G
Amphenol		Receptacle	Motor		N	Fan
				E	A	Thermal
					L	Sensor
T				SNUBBER			CONTROL
	S						BOARD		MODE
R				FAN
	T
E
M	R	115VAC		BOARD					SWITCH
I	I
N	P
A
L				GATE SIGNAL
							F
42VAC
							E
							E
MAIN							D
							B
TRANSFORMER							A
							C		POSITIVE
							K
									TERMINAL
							SHUNT	F
								E
								E
42VAC 10VAC10VAC							LATCHING	D
							RESISTOR	B
				SCR BRIDGE				A	HIGH
								C	NEGATIVE
						CHOKE		K	TERMINAL
TO OPTIONAL
METER BOARD
									LOW

IDEALARC DC-655