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Section E-1 Section E-1
Theory of Operation...............................................................................................Section E
General Description ......................................................................................................E-2
Input Power Circuit.......................................................................................................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
TABLE OF CONTENTS
- THEORY OF OPERATION SECTION -
FIGURE E.1 – PRECISION TIG 185 BLOCK LOGIC DIAGRAM
INPUT
POWER
SWITCH
MAIN
TRANSFORMER
POLARITY
SWITCH
SCR
BRIDGE
X1
X2
AC
AC
DC+
DC-
CONTROL
BOARD
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
H1
H2
H3
SHUNT
115VAC
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
BY-PASS
BOARD
HI-FREQUENCY
TRANSFORMER
C
H
O
K
E
WORK
ELECTRODE
THERMAL
LIGHT
GAS
VALVE
THERMO-
STATS
OUTPUT
CONTROL
MODE
SWITCH
POWER
"ON"
DIGITAL
DISPLAY
F
E
E
D
B
A
C
K
AUTO
BALANCE
LED
TIG
LED
STICK
LED
PULSE
FREQ.
LED
BYPASS
ASBLY
AC
BALANCE
CONTROL
PULSE
CONTROL
POSTFLOW
CONTROL