irf9540 mosfet test(p-channel) - diyAudio
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Old 1st February 2004, 08:16 AM   #1
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Default irf9540 mosfet test(p-channel)

i do all of the following...

"connect the meter negative to the MOSFET's source. This is arrowed in the drawing above which shows the most popular TO220 MOSFETs.

Hold the MOSFET by the case or the tab if you wish, it doesn't matter if you touch the metal body but be careful not to touch the leads until you need to.

First touch the meter positive on to the gate.

Now move the positive meter probe to the drain. You should get a low reading. The MOSFET's gate capacitance has been charged up by the meter and the device is turned on.

With the meter positive still connected to the drain, touch a finger between source and gate (and drain if you wish, it matters not). The gate will be discharged through your finger and the meter reading should go high, indicating a non-conducting device. "

...but when i try to discharge the gate,it doesn't discharge.do you think the mosfet is damaged or do i test the wrong way?

i tried the same for the irf540 and works!!!

p.s. the mosfets(irf540 and irf9540) are part of Rockford 451s amplifier output stage.the problems started when i connected invert polarity the power wires
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Old 2nd February 2004, 09:35 PM   #2
ukram is offline ukram  Finland
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Join Date: Jun 2003
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Try measuring the resistance between fet pins. I had some failed fets that had shorts between (all?) pins in my old Onkyo A-8067 amp. That amp was the reason for building my own amp, which has NOT had any problems, about 6 months old now. I still have a bunch of FETs that i bought for repairs. If you get about zero resistance from gate to some other pin, then the FET has certainly failed.
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