Lincoln Electric Precision TIG 375, Service Manual, Page: 39 / 143

E-1 E-1
PRECISION TIG 375
Theory of Operation .............................................................................................................. Section E
General Description ....................................................................................................................E-2
Input Power Circuit ......................................................................................................................E-2
Output Rectification, Control Board and Feedback.....................................................................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
Fan As Needed (F.A.N.)........................................................................................................E-8
Thermal Protection ...............................................................................................................E-8
Overload Protection ..............................................................................................................E-8
TABLE OF CONTENTS
-THEORY OF OPERATION SECTION-
POWER
SWITCH
RECONNECT PANEL
OPTIONAL POWER
FACTOR
POLARITY
SWITCH
BYPASS BOARD
WORK
FRONT
ELECTRODE
REAR
ELECTRODE
78 VAC
X1
X2
AC
AC
DC
DC
SHUNT
CHOKE
HIGH FREQUENCY
TRANSFORMER
HIGH VOLTAGE
TRANSFORMER
THERMOSTAT
115 VAC
115 VAC
115 VAC
FANS
GATE LEADS
FEEDBACK
GAS
SOLENOID
115 VAC
115 VAC
LED's
THERMOSTATS
20 VAC
20 VAC
CONTROL BOARD
BACKGROUND
CIRCUIT
FROM
CONTROL
BOARD
63.5 VAC
CORRECTION
CAPACITORS
REAR GANG
SCR
BRIDGE
ADVANCED CONTROL
PANEL RECEPTACLE
MINIMUM
OUTPUT
CONTROL
MAXIMUM
OUTPUT
CONTROL
PROTECTION
BOARD
REMOTE
RECEPTACLE
METER
STICK
TIG
SWITCH
BALANCE
CONTROL
POST
FLOW
LOCAL/REMOTE
SWITCH
Precision Tig 375
FROM CONTROL BOARD
X3
STICK OCV BOOST
CIRCUIT
HIGH FREQUENCY
INTENSITY ADJUSTMENT
FIGURE E.1 – PRECISION TIG 375 BLOCK LOGIC DIAGRAM
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