Lincoln Electric POWER MIG SVM167-A Service Manual page 34

E-4
FAN
MOTOR
LINE
SWITCH
RECONNECT
PANEL
TRANSFORMER
CONTROL BOARD, GUN
TRIGGER AND WIRE DRIVE
MOTOR
When the control board receives an activation
command from the trigger circuit the control
board supplies 12VDC which activates the gas
solenoid and output contactor. It also supplies
2 to 29 VDC (depending on the wire speed
setting) to the wire drive motor. The control
board monitors 0-5VDC signal from the wire
speed potentiometer and adjusts the motor
speed accordingly. The proper armature voltage
is then applied to the wire drive motor. The drive
motor speed is thus controlled which in turn
regulates the electrode wire feed speed through
the gun.
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
THEORY OF OPERATION
FIGURE E.4 – OPTIONAL CIRCUITS.
GAS
SOLENOID
CONTROL BOARD
RECTIFIER
DIODE
BRIDGE
TAP SELECTOR
SWITCH
CONTACTOR
MAIN
POWER MIG® 215
WIRE
SPEED
CONTROL
WIRE
DRIVE
MOTOR
TRANSFORMER
TACH
THERMOSTAT
GUN TRIGGER
OUTPUT DIODE
BRIDGE
+
+
OUTPUT
POSITIVE
CHOKE
TERMINAL
OUTPUT
CAPACITORS
- -
NEGATIVE
TERMINAL
Two self re-setting thermostats are included in
the trigger circuitry.
thermostats would "open" due to excessive heat,
the trigger circuit would be interrupted and the
machine's output and the wire feed would be
disabled. The board also contains overload
protection circuitry which protects the drive
motor from excessive current draw.
E-4
OUTPUT BRIDGE
THERMOSTAT
GUN
ASSEMBLY
If either of these