ESAB LTR 160, Service Manual

Page: 30 / 46

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TRANSISTOR BOARD AP03
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Simpified circuit diagram for transistor board AP03 (negative)
The --880 variant is used in the LTR 160 and the --882 variant is used in the LTR 200..
Individual transistors must not be replaced: if the circuit board is faulty, it must be replaced
in its entirety. In addition, circuit board AP02 must also be replaced.
See page 37 for instructions for removing and fitting the circuit board.
A01, A02 Connections A01 -- A02 are for the gate pulses from circuit board AP01.
B01, B02
When the machine is loaded, pulses from a trigger pulse winding on main
transformer TC02 are supplied to connections B01 and B02, for use as gate
pulses in controlling thyristor TY1.
D1 -- D3 Transient voltage protection.
D5
Back--emf protection diode (squelch diode), for main transformer TC02
when the transistors turn off.
Q1 -- Q8 MOSFET transistors. These require a special instrument.
See MOS TESTER on page 32 for testing.
Due to a change to transistors with higher current rating, the circuit board
may have one transistor less than specified in the diagram above.