Re: [CAD_CAM_EDM_DRO] Re: How do I check the MOSFET's in my stepper driver

Mariss Freimanis wrote:

>1) Set your multimeter to Ohms.
>2) Disconnect the motor and power supply from the drive.
>3) Connect one meter lead to drive power supply ground.
>4) Measure the resistance at each of the 4 outputs.
>5) Move the lead from ground to drive + supply input.
>6) Repeat (4)
>
>Transistors invariably fail shorted. If one or more of the 8
>measurements you took show a short then the drive has 1 or more
>damaged power transistors.
>
>

I haven't seen this in 80 V stepper or servo drives, but in some 400 V
inverter drives I designed some years ago (very similar full-bridge switch
circuits, though) I have on a few occasions had blown transistors that were
in the open condition AFTER a fault. Of course, these transistors were open
in more than the electrical sense! They sounded like a pistol going
off, indoors,
and glowing pieces were embedded in the walls.

(Yes, Mariss is correct above, the transistors shorted first, then were
exploded
by shorting the energy in the filter caps.)

Jon