TESTING A 40673 DUAL GATE MOSFET

[cobra149]

Hi,
please can any one tell me how to test if a 40673 mosfet is blown.
Can I test this with a digital multimeter, if so how do I go about it ?.

Pic attached.

Thank you.

[Hero999]

It's a depletion MOSFET.

It's normally on (low resistance between the drain and source) when the gate voltage is zero. When the voltage on the gates is negative with respect to the source, there will be a high resistance between the drain and source. The resistance between the gates and drain/source should always be infinite.

You can test it using the meter's resistance setting and bias the gate with a 6V battery or a small power supply, 5V will do.

http://www.angelfire.com/electronic2/index1/40673.pdf

[cobra149]

Hi,
thanks for the reply, though I should have mentioned that I am a complete novice in electronics.
I am not quite sure of what you mean, do I apply 5 volts directly to one of the gate legs ?.
And if I see a high resistance ....is the mosfet in good condition ?.

Sorry for my lack of knowledge on this matter , and thank you for your reply

[Hero999]

Firstly, measure the resistance between both gates (connect them together) and drain and source, the resistance should be near infinite, >100M.

Secondly connect both of the gates to the drain. Measure the resistance between the drain (meter positive) and the source meter negative), it should be under 1k.

Finally connect the 5V supply's positive to the source and negative to the gates. Measure the source - drain resistance, it should be much higher than the previous measurement >1M.

[cobra149]

@Hero999 Thank you so much.
I have tested the 40673 re your instructions and it is indeed faulty.

Thanks and regards