ESAB Aristotig 405 AC/DC, Service Manual

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9 TESTING OF A4, A5, A9, A10, A11, A12, A13, A14
Using a digital multimeter, you can test the gate connections of primary switch A4, A5, A11, A12
and inverter A9, A10, A13, A14.
If there are defects in power transistors, the gate source resistors usually change from >0.001
Ω
to levels of less than 100
Ω
. On all power boards A4, A5, A9, A10, A11, A12, A13, A14, 1 k
Ω
pro-
tective resistors are installed in parallel with the control inputs.
When power modules are connected in parallel, the resistance decreases to 500
Ω
.
If the resistor values are correct, the power section is in all probability OK.
For measuring, disconnect the control connecting leads to the power transistors from the power
boards or from the associated control boards.
• Control board connections:
A1: X11, X12
• A8: X6, X7
NOTES: