Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 46

E-2
FIGURE E.2 - INPUT VOLTAGE, CONTACTOR, RECONNECT PANEL, PILOT TRANSFORMER,
CONTROL TRANSFORMER, POWER FACTOR CAPACITORS AND MAIN TRANSFORMER
HIGH FREQUENCY SPARK
ELECTRODE SENSE
PANEL
SWITCHES
HIGH VOLTAGE
115VAC
TRANSFORMER
REMOTE
CIRCUIT
FEED - THRU
RECEPTACLE
BOARD
GAS/WATER
SOLENOIDS
115VAC
INTERLOCK
FANS 115VAC
RECEPTACLE
INPUT
R
CONTACTOR
E
C
O
N
N
E
C
T
START/
STOP
PILOT
TRANSFORMER
GENERAL DESCRIPTION
The Square Wave TIG 355 is a constant current, single
range square wave AC/DC TIG (GTAW) arc welding
power source with built-in high frequency stabilization.
It also has stick (SMAW) capability. The Square Wave
TIG 355 gives the operator full control of the welding
current plus the ability to preset weld and start cur-
rents. Preflow and postflow timers are included for
shielding gas and cooling water control. Altogether the
many features of the machine allow part or all of a weld
cycle to be preset or "programmed," which simplifies
the TIG welding process.
INPUT POWER CIRCUIT
The desired single-phase input power is connected to
the TIG 355 through an input contactor located in the
rear of the machine. The input power is also con-
nected directly to the pilot transformer, which supplies
115VAC for the input contactor interlock and start/ stop
circuits.
THEORY OF OPERATION
UPPER LOWER
DISPLAY
CONTROL
CONTROL
BOARD
PANEL PANEL
SCR GATE COMMANDS
ELECTRODE
SENSE
15VDC
CONTROL
TRIGGER
BOARD
INTERLOCK
REMOTE
COMMANDS
HI-FREQ/ WATER/GAS
COMMANDS
INTERLOCK
115VAC - HI-FREQ AND GAS/WATER
115VAC
CONTROL TRANSFORMER
115VAC
AC
AC
POWER
FACTOR
CAPACITORS
POLARITY
MAIN
TRANSFORMER
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
SQUARE WAVE TIG 355
STATUS
BOARD
POWER
BOARD
SNUBBER
BOARD
DC-
C
H
DC+
O
K
E
BY-PASS
BOARDS
SWITCH
SHUNT
A reconnect panel allows the user to configure the pilot
transformer, the power factor capacitors, and the main
transformer for the desired input voltage.
input voltage is applied, through the input contactor, to
the primary of the main transformer. The power factor
correction capacitors are incorporated in the primary
circuit of the main transformer to help balance the
inductive nature of the TIG 355. The main transformer
changes the high voltage, low current input power to a
low voltage, high current output.
In addition, the main transformer also has an isolated
115VAC auxiliary winding that supplies power to oper-
ate the cooling fans and offers 15 amps of auxiliary
power at the 115VAC receptacle. This 115VAC is also
applied, through the feed-thru board, to the power
board for high voltage and gas/water solenoid opera-
tion.
The control transformer primary is also powered by the
115VAC winding in the main transformer. The sec-
ondary voltages that are developed in the control trans-
former supply power to the control and power boards.
E-2
WORK
ELECTRODE
HI-FREQ
TRANSFORMER
This AC