Lincoln Electric 11519 Service Manual page 43

E-5
AUX
115 VAC
LINE
SWITCH
RECONNECT
TRANSFORMER
WIRE DRIVE MOTOR
AND FEEDBACK
The wire drive motor is controlled by the control board.
A motor speed feedback signal is generated at the
motor tach and sent to the control board. The control
board compares this feedback signal with the com-
mands set forth by the Wire Speed Control poten-
tiometer and sends the appropriate armature voltage to
the wire drive motor. The drive motor speed is thus
controlled which in turn regulates the electrode wire
feed speed through the gun.
THEORY OF OPERATION
FIGURE E.5 — WIRE DRIVE MOTOR AND FEEDBACK
GAS
MOTOR
SOLENOID
WIRE
SPEED
CONTROL
ARC
BOARD
VOLTAGE
RECTIFIER
DIODE
G
BRIDGE
A
T
30 VAC
E
SNUBBER
S
BOARD
I
G
N
A
L
ENHANCEMENT
MAIN
SCR
RECTIFIER
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
Power MIG® 255XT
SPOOL
FAN
GUN
WIRE
DRIVE
MOTOR
TACH
TIMER ASSEMBLY
GUN TRIGGER
FEEDBACK
POWER
C OUTPUT
F
A CHOKE
TERMINAL
E
CHOKE
P
E
A
D
C
B
I
A
T
C
O
K
R
S
SHUNT
The control board also provides a 3-24 VDC operating
voltage for the optional spool gun. To achieve full WFS
control at the spool gun, the WFS knob on front of the
PM-255XT must be set at max.
POSITIVE
NEGATIVE
TERMINAL
E-5