Lincoln Electric WIRE-MATIC 255 SVM 119-A Service Manual page 46

E-3
MAIN
LINE
TRANSFORMER
SWITCH
RECONNECT
FAN
MOTORS
CONSTANT VOLTAGE OUTPUT
The controlled DC output from the SCR rectifier
assembly is filtered by the capacitor bank resulting is a
constant voltage DC output. Since the output choke is
in series with the positive leg of the rectifier and also in
series with the gun and welding load, a filtered con-
stant voltage output is applied to the output terminals
of the machine.
THEORY OF OPERATION
CONSTANT VOLTAGE OUTPUT
WIRE GAS
SPEED SOLENOID
ARC
VOLTAGE
CONTROL BOARD
G
A
T
E
S
I
G
N
A
L
SCR
RECTIFIER
Figure E.4 - Constant Voltage Output.
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
WIRE-MATIC 255
WIRE
DRIVE
MOTOR
TACH
GUN TRIGGER AND THUMB SWITCH
FEEDBACK
POSITIVE
TERMINAL
CHOKE
C
A F
P E
A E
C D
I B
T A
O C
R K
NEGATIVE
S
TERMINAL
SHUNT
E-3