Lincoln Electric Precision TIG 375, Service Manual, Page: 42 / 143

E-4 E-4
PRECISION TIG 375
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THEORY OF OPERATION
FIGURE E.4 – HIGH VOLTAGE / HIGH FREQUENCY CIRCUIT
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
HIGH VOLTAGE/HIGH FREQUENCY
CIRCUIT
The control board passes the 115 VAC voltage to the
primary of the high voltage transformer. The secondary
of the high voltage transformer is coupled to a spark
gap generator and also to the primary winding of the
high frequency transformer. The secondary of the high
frequency transformer is in series with the rear elec-
trode output terminal. The high frequency “spark” is
present at the electrode terminal and is transferred to
the Tig torch.
The Precision TIG 375 has a high frequency adjust-
ment that allows the operator to control the intensity of
the high frequency circuit.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.