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cmek0de1
Sections 1--16 below refer to the /wiring diagrams on pages 5 and 6.
The circuit board is screened by a metal casing, connected to 0 V in the wire feed unit.
1
Power supply
cmek0e05
The wire feed unit receives 42 V from the control power supply transformer in the
welding power unit via connector XP01. LAW 400 and 500 welding power units
can supply a maximum of 6 A to the MEK 4. The wire feed unit’s own power
requirement at maximum load is 5 A.
42 V AC is supplied to the welding gun trigger switch, the gas valve and the
contactor. In addition, terminals G01 and G02 supply 42 V to a Miggytrac unit if
this is used together with the MEK 4.
DC power supplies
Diodes D30 -- D33 rectify the 42 V supply to 60 V. Capacitor C61 smooths the
supply, which is then used to power the wire feeder motor.
Transistor Q2 is a pre--regulator that drops the voltage from 60 V to 20 V. Q2 is
current--limited to about 200 mA.
VR1 and VR2 are voltage regulators, producing 5 V and 15 V respectively. The
circuit board’s microprocessor monitors the voltages. If the 15 V supply falls below
13 V, the wire feed unit is stopped.
2
Activation, contactor
cmek0e06
The welding power unit contactor is connected to the wire feed unit via pin F in
connector XP01. In the LAW 400/500 power units triac TC1 is loaded by a 1 k
Ω
resistor.
