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E-1E-1
PRECISION TIG 275
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
W
ORK
FRONT
ELECTRODE
REAR
ELECTRODE
78 VAC
X1
X
2
AC
AC
DC
DC
SHUNT
CHOKE
HIGH FREQUENCY
TRANSFORMER
HIGH VOLTAGE
TRANSFORMER
THERMOSTAT
115 VAC
115 VAC
115 VAC
FAN
GATE LEADS
FEEDBACK
GAS
SOLENOID
115 VAC
115 VAC
LED's
THERMOSTAT
20 VAC
20 VAC
CONTROL BOARD
BACKGROUND
CIRCUIT
FROM
C
ONTROL
BOARD
63.5 VAC
CORRECTION
CAPACITORS
R
EAR 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
FIGURE E.1 – PRECISION TIG 275 BLOCK LOGIC DIAGRAM