Thank you for the reply...

I believe that answers my question (that the 0.001 to 0.003 readings
are normal), and yes when the gate is discharged it is giving an
infinity reading.

I guess I will keep troubleshooting this UPS, my next guess is that the
LM324 that is driving the two MOSFETS isn't giving them the correct
waveform or isn't being told to give them the correct waveform.


Thanks again,

-Landon

John Musselman wrote:
Landon,

That's a cute procedure and may even work.

In the "diode test" position, your DVM is generating a small current and
reading what voltage is generated. So a diode will read out the voltage
across the junction (the "forward voltage" or Vf) with this current passing
through. In a diode, this tends to be 0.5 to 0.7 for a silicon diode, and
varies little with the current.

In a MOSFET, there isn't a diode junction. It's just like a resistor, so a
low reading is a low resistance. (A low voltage is generated by the test
current). The low number is OK, if you have, indeed, charged the gate. You
should get a high reading (or overload, or infinity) when the gate is
discharged or shorted to ground.

John


"Landon" wrote in message
...

Hi, thanks for replying.

I found a procedure online somewhere that basically said the following:

------------------------------------------------------------------------
-Set meter to check diodes.
-Put positive lead on the GATE, put negative lead on the SOURCE (this will
charge the gate, before doing this the DRAIN and SOURCE pins should give a
HIGH reading).
-Then move the positve lead to the DRAIN, it should give a LOW reading.
-Touch the GATE and SOURCE pins with finger tip, the gate should
discharge, then the DRAIN and SOURCE pins should again give a HIGH
reading.
------------------------------------------------------------------------

This is where I am stuck, the Mosfets are acting the way the test says
that they should but I am used to seeing diodes reading at 0.5xx to
0.7xx, these are reading at 0.001 and 0.003, I'm not sure if this is too
low or right where it should be.

-Landon