Test mosfet with digital and analog multimeter
A power component has high current , high wattage may be broken as shorted condition and open condition. Before other process testing , you may firstly check shorted condition and open condition. Testing mosfet has some detail and all steps of testing must be good so it is a good mosfet. If any of only testing step is fail , the mosfet is already broken.
N Channel MOSFET Symbol
P Channel MOSFET Symbol
Step to test mosfet with a digital multimeter
1. Discharge mosfet . short 3 terminals D-G-S together by using resistor legs or other metal wire. then remove resistor leg. After shorting 3 terminals , do not touch any mosfet terminal again. If you touch it by error , it must re-discharge. The area which can touch and hold is the black case of mosfet.
2. Test G and D terminal , read the measured value. Switch the test lead and read the measured value again. A good mosfet , meter will display "OL" 2 time.
Discharge mosfet . short 3 terminals D-G-S together , G D S is terminal arrangment.
Test G and D terminal. The first testing.
Test G and D terminal. The second testing ( switch the test lead)
3. Test G and S terminal , read the measured value. Switch the test lead and read the measured value again. A good mosfet , meter will display " OL" 2 time.
Test G and S terminal. The first testing.
Test G and D terminal. The second testing ( switch test lead)
4. Test D and S terminal. Use Ohm range to test D and S terminal and read the measured value. then switch the test lead and test again. A good mosfet will display " OL " 1 time and display high resistance 1 time. Some model of mosfet has internal diode connect across D and S terminal , this case you can use diode range to test it. Bad mosfet will display differnt ways that is , shored will display very low resistance 0 Ohm 2 time , open mosfet will display " OL" 2 time.
Test D and S terminal. Use Ohm range will display high resistance 1 time.
Test D and S terminal. Use Ohm range will display " OL " 1 time.
Please be careful after discharge mosfet ,don't touch any terminal. Always hold mosfet at insultated case.
Step to test mosfet with a digital multimeter
1. Discharge mosfet . short 3 terminals D-G-S together by using resistor legs or other metal wire. then remove resistor leg. After short 3 terminals , do not touch any mosfet terminal again. If you touch it by error , it must re-discharge. The area which can touch and hold is black case of mosfet.
2. Test G and D terminal. Set range to Rx10K and do zero ohm adjustment. Connect test lead with D and G terminal then read the measured value. Switch the test lead and read the measured value again.
Good mosfet , the pointer will point at ∞ 2 time.
3. Test G and S terminal. Set range to Rx10K and do zero ohm adjustment. Connect test lead with G and S terminal then read the measured value. Switch the test lead and read the measured value again.
Good mosfet ,the pointer will point at ∞ 2 time.
Test G and D terminal. Good mosfet , the pointer will point at ∞ 2 time.
Test G and S terminal. Good mosfet , the pointer will point at ∞ 2 time.
4. Test D and S terminal. Set range to Rx10 ( or Rx100 ) and do zero ohm adjustment. connect test lead with D and S terminal then read the measured value. Switch the test lead and read the measured value again.
Good mosfet ,the pointer will point at low resistance 1 time.
Good mosfet ,the pointer will point at ∞ (or high resistance ) 1 time.
( some model it will point at high resistance instead of ∞ )
Good mosfet ,the pointer will point at low resistance 1 time.
Good mosfet ,the pointer will point at ∞ (or high resistance ) 1 time.
Bad mosfet when test D and S terminal , shored condition will display 0 ohm 2 time.
Open condition will display ∞ 2 time.
Shored mosfet will display 0 ohm 2 time when test D and S terminal
Open mosfet will display ∞ 2 time when test D and S terminal
