
E-6
E-6
PRECISION TIG 375
AC WELDING OUTPUT
Rotating the polarity switch to the AC position changes
the welding power circuit. One lead (X1) of the main
transformer secondary is connected to the machine’s
output work terminal. The other secondary lead (X2) is
connected to one of the AC connections of the SCR
bridge. The electrode terminal is connected to the
other AC side of the bridge. The choke is now
electrically across the negative and positive SCR
bridge connections. With the ability of the choke to
store energy and the SCRs to turn on at the appropri-
ate times, an AC square wave is developed and applied
to the output terminals. The bypass board protects the
internal circuitry from interference.
THEORY OF OPERATION
FIGURE E.7 – AC WELDING OUTPUT
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.8 DC WELDING CURRENT GENERATION
G
CHOKE
ELECTRODE
WORK
DC
PRIMARY
10
G
G
G
NOTE:
Unshaded areas of Block Logic Diagram are the subject of discussion.