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THEORY OF OPERATION
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PRINTED CIRCUIT BOARD
FUNCTIONS
POWER BOARD
The input power (115VAC) is applied to the power board, and from that the power board develops the DC field voltage for the wire drive motor. The SCR circuit- ry, used to control the motor armature voltage, is also contained on the power board.
The relay used to activate motor armature voltage, field voltage, auxiliary output on terminals
The rectified and regulated power supplies, used for the
The shut down, start response and trigger interlock cir- cuitry, in addition to the rectified and regulated power supplies used for the
CONTROL BOARD
The control board provides a reference voltage to the wire speed control and voltage control potentiometers, allowing SET signals to be produced.
The control board also powers and processes the feed- back signals from the tachometer board. It compares the actual speed information to the SET speed com- mand signal and develops firing pulses that drive the motor armature SCR circuitry, located on the power board.
Initial acceleration rates for wire feed speed are con- trolled by the control board as well as the SET speed and actual speed signals for the digital meter circuitry.
VOLTAGE BOARD
The voltage board compares the SET voltage values to the actual voltage values and makes any necessary correction by sending the appropriate signal to the Lincoln CV power source. If for any reason the arc voltage cannot be controlled to the SET voltage, the voltage board interrupts the
TRIGGER BOARD
The trigger transformer supplies 24VAC to the trigger board where it is rectified and regulated to 20VDC. This DC voltage is used in the gun trigger circuit to ini- tiate the welding operation.
TACHOMETER BOARD
A square wave frequency signal, proportional to motor speed, is generated by the tachometer board and sent to the control board.
METER BOARD
The meter board contains signal scaling and power supply circuitry for the digital meter.
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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.