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Electronics => Repair => Topic started by: Bargainhunter on May 27, 2015, 01:12:20 pm

Title: Help with testing MOSFET
Post by: Bargainhunter on May 27, 2015, 01:12:20 pm

Hi,
I am troubleshooting a Panasonic PT-AE4000U power supply.  I tried testing the MOSFET K3561 with my DMM in diode setting and the mosfet didn't turn on.  I order a new 2sk3561 and it would not turn on either.  I tried three different DMM's.  What is going on?  Do my DMM's not have enought voltage to turn on the K3561 or what?
I have an old Heathkit IT-121 transistor tester that will test FET semiconductors.  Do you think that will test MOSFETs?

Any help would be greatly appreciated.

Title: Re: Help with testing MOSFET
Post by: Seekonk on May 27, 2015, 01:20:57 pm

Generally you need over three volts to turn on a FET, some even higher. Your DVM likely can't supply enough voltage.  A 9V battery connected to a 250K to 1M pot as a voltage divider would make a useful test device and then use a DVM to measure ohms.

Title: Re: Help with testing MOSFET
Post by: w2aew on May 27, 2015, 01:39:03 pm

You might want to look at my video on this.  The first 2.5 minutes describes the DMM method, the second half of the video shows a different method using a few simple components:

https://www.youtube.com/watch?v=gloikp9t2dA (https://www.youtube.com/watch?v=gloikp9t2dA)

Title: Re: Help with testing MOSFET
Post by: darkness_electro on May 27, 2015, 03:52:03 pm

You could build on a breadbord or something a circuit that supplies 5v on the gate and turns on an LED. Quite simple.