Lincoln Electric MULTI-SOURCE SVM155-A Service Manual page 23

Section E-1
Theory of Operation Section ...............................................................................................Section E
General Description ..............................................................................................................E-2
Input Voltage, Filter, Contactor and Control Transformer ....................................................E-2
Main Transformer, Control Board, Cooling Fan Motor, Digital Meter & LED's .....................E-3
SCR Bridge, Resistor Bank, Firing Board, & Output Capacitor/Resistor ............................E-4
Protection Devices & Circuits...............................................................................................E-5
SCR Operation .....................................................................................................................E-6
SURGE
NOISE
FILTER
INPUT
CONTACTOR
T2
CONTROL
TRANSFORMER
THERMOSTAT SWITCH
TABLE OF CONTENTS
-THEORY OF OPERATION-
FIGURE E.1 – MULTI-SOURCE BLOCK LOGIC DIAGRAM
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
CONTROL
BOX
RECTIFIER
CONTROL
BOARD
FAN
G Y
DIGITAL
LED LED LED
METER
MULTI-SOURCE
T1
SCR OUTPUT RECTIFIER
SHUNT
TO CONTROL
BOARD
GATE SIGNALS
RESISTOR
BANK
CONTROL
THERMOSTAT SIGNAL
W
Section E-1
WORK
TERMINAL
FILTER
CAPACITOR
LIMITING
RESISTOR
ELECTRODE
TERMINAL
TO CONTROL
BOARD
FIRING
BOARD