Lincoln Electric IDEALARC DC-655 Service Manual page 37

Section E-1
-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
CONTROL
TRANSFORMER
115VAC
CR2
R
E
C
O
N
N
E
C
T
CONTACTOR
CR1
TABLE OF CONTENTS
FIGURE E.1 – DC-655 BLOCK LOGIC DIAGRAM
42VAC
CONTROL
BOARD
TRANSFORMER
FAULT PROTECTION
32VAC
32VAC
32VAC
Fan
14-pin 115VAC
Amphenol Receptacle Motor
T
S
E
T
R
115VAC
R
M
I
I
P
N
A
L
42VAC
MAIN
TRANSFORMER
42VAC 10VAC10VAC
TO OPTIONAL
METER BOARD
IDEALARC DC-655
CONTROL
OUTPUT
CONTROL SIGNAL
FIRING
BOARD
S
G
I
A
G
T
Fan
N
E
Thermal
A
Sensor
L
CONTROL
SNUBBER
BOARD
FAN
BOARD
GATE SIGNAL
F
E
E
D
B
A
C
K
SHUNT
LATCHING
RESISTOR
SCR BRIDGE
CHOKE
Section E-1
OUTPUT
ARC FORCE
CONTROL
MODE
SWITCH
POSITIVE
TERMINAL
F
E
E
D
B
A
HIGH
C NEGATIVE
TERMINAL
K
LOW