Lincoln Electric SVM188-A Service Manual page 35

E-1 TABLE OF CONTENTS-THEORY OF OPERATION SECTION
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1
General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2
Input Circuit and Main Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2
Control Circuit, Firing Circuit and Rectifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-3
Protective Devices and Shutdown Circuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-4
SCR Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-5
POWER
CONTROL
TRANSFORMER
SWITCH
115VAC
•
Pilot
Light
w
CR2
•
Secondary
Thermostat
Primary
Theromstat
1CR Coil
R
E
C
O
N
N
E
C
T
CONTACTOR
CR1
FIGURE E.1 BLOCK LOGIC DIAGRAM
FAULT PROTECTION
32VAC
FIRING
32VAC
BOARD
32VAC
G
A
14-pin
Fan
115VAC
T
Amphenol Receptacle Motor
E
T • 115VAC
S
E
T
R
R
M
OUTPUT
I
I
P
N
TERMINAL
A
2
L
SWITCH
42VAC
115VAC
MAIN
TRANSFORMER
SCR BRIDGE
DC-600
TERMINAL
STRIP 1
OUTPUT
CONTROL
OUTPUT
CONTROL SIGNAL
S
I
G
N
A
L
CONTROL
BOARD
F
E
E
D
B
A
C
K
SHUNT
LATCHING
RESISTOR
CHOKE
E-1
OUTPUT
CONTROL
SWITCH
MODE
SWITCH
POSITIVE
TERMINAL
F
E
E
D
B
A
NEGATIVE
C
TERMINAL
K