Lincoln Electric SQUARE WAVE SVM118-A Service Manual page 42

Section E-1
-THEORY OF OPERATION SECTION-
Theory of Operation .............................................................................................................Section E
General Description ....................................................................................................................E-2
Input Power Circuit:
Input Voltage, Contactor, Reconnect Panel, Pilot Transformer, Control Transformer,
Power Factor Capacitors, and Main Transformer.......................................................................E-2
Output Rectification and Feedback Control ...............................................................................E-3
High Voltage/High Frequency Circuit..........................................................................................E-4
DC Welding Output .....................................................................................................................E-5
AC Welding Output .....................................................................................................................E-6
SCR Operation ............................................................................................................................E-7
Protective Circuits.......................................................................................................................E-8
Thermal Protection ...............................................................................................................E-8
Overload Protection..............................................................................................................E-8
FIGURE E.1 - SQUARE WAVE TIG BLOCK LOGIC DIAGRAM
HIGH VOLTAGE
115VAC
TRANSFORMER
REMOTE
CIRCUIT
RECEPTACLE
GAS/WATER
SOLENOIDS
115VAC
INTERLOCK
FANS
INPUT
CONTACTOR
START/
STOP
PILOT
TRANSFORMER
TABLE OF CONTENTS
HIGH FREQUENCY SPARK
ELECTRODE SENSE
UPPER LOWER
PANEL
CONTROL CONTROL
SWITCHES
PANEL PANEL
ELECTRODE
SENSE
FEED - THRU CONTROL
TRIGGER
BOARD BOARD
REMOTE
COMMANDS
INTERLOCK
HI-FREQ AND GAS/WATER
115VAC -
115VAC 115VAC
RECEPTACLE
CONTROL TRANSFORMER
115VAC
R
E
C
O
N
POWER
N
FACTOR
E
CAPACITORS
C
T
MAIN
TRANSFORMER
SQUARE WAVE TIG 355
DISPLAY STATUS
BOARD BOARD
SCR GATE COMMANDS
15VDC
POWER
BOARD
INTERLOCK
HI-FREQ/ WATER/GAS
COMMANDS
SNUBBER
BOARD
DC-
AC
C
H
AC
DC+
O
K
E
POLARITY
SWITCH
SHUNT
Section E-1
BY-PASS
BOARDS WORK
ELECTRODE
HI-FREQ
TRANSFORMER