ESAB LKA 150, Руководство по обслуживанию

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COMPONENT POSITIONS, CIRCUIT BOARD AP1
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DESCRIPTION OF OPERATION, CIRCUIT BOARD AP1
This description relates to the circuit diagram and the component positions diagram.
If the circuit board is faulty, it must be replaced.
1
CONTROL CIRCUIT
Pressing trigger switch SB1 on the welding torch energises relay RE1 from control
power transformer TR1. The contacts on the relay connect main transformer TM1 to
the mains power supply.
The power supply to RE1 is half − wave rectified by D1. Resistor R1 is connected in
series with the relay and drops the voltage to it. Capacitor C1 (220 µ F) smoothes the
voltage. It also delays the drop − off of relay RE1 by about 25 ms, to provide a
back − burn time.
2
THERMAL OVERLOAD CUTOUT
In the event of a thermal overload, thermal overload cutouts ST1 or ST2 interrupt the
secondary circuit from TR1, causing relay RE1 to drop off and de − energising the
welding circuit.
When not operated (i.e. with closed contacts), the cutouts short − circuit inputs
B6 and B7.
Operation of either of the cutouts is indicated by LED V1. Interruption of the cutout
circuit energises the LED via D2, R3 and D3. D2 is a half − wave rectifier, R3 limits
the current through the LED and D3 protects it against reverse voltage.