Electrical maintenance and repair EEC 226

Explain how to use an analogue multimeter to test Diode, PNP, NPN transistor, polarised and non-polarized capacitor

Explain how to use an analogue multimeter
(1) To test non-polarized capacitors.
(2) To test NPN transistor.
(3) to test Diode
(4) To test PNP transistor
(5) To test a polarised capacitor

(1) To test non-polarized capacitors: You can know when the resistance of the capacitor is less than about 1MΩ, and allows d.c to pass From the battery in the multimeter i.e it is leaking and faulty. (2 marks)

(2) To test NPN transistor: suppose your ohmmeter test shows high resistance with the negative ohmmeter connected to the base of the transistor and the other lead is switched from transistor lead
Continue testing as follows;
(I) Reverse the ohmmeter leads, connecting the positive lead to the base of the transistor.
(II) connect the negative lead from the ohmmeter first to the transistor lead, then to the other.
(III) if both reading, show low resistance you have an NPN transistor.

(3) Diode: The multimeter can be used to measure the goodness or otherwise of a diode. The ohmic section (Ω range) of the meter is used. After the zeroing adjustment, the forward resistance is measured this should read LOW, while the reversed resistance is also taken, this is to read HIGH ( i.e there should be high reading in one direction and low reading in the other direction) to indicate that the diode is healthy (good) one.


(4) To test PNP transistor: Supposed you have a transistor to install, but cannot tell whether it is PNP or NPN. First, make sure that you know which is the positive lead and which is the negative lead of your ohmmeter. If necessary, take off the back of the instrument and check the polarity of the battery against the lead connection (i.e positive-positive and negative-negative)
Steps to take;
(I) hook the positive lead from the ohmmeter to the base of the transistor.
(II) Connect the negative lead from the ohmmeter first to one transistor lead, then to the other.
(III) if both readings show high resistance, hook the negative ohmmeter leads to the base of the transistor.
(IV) connect the positive lead from the ohmmeter first to one transistor lead, then to the other one.
(V) if both readings show low resistance, you have a PNP transistor.


(5) To test a polarised capacitor: for the dielectric to form in this, a positive voltage must be applied to the positive lead of the capacitor (marked by a+) from the multimeter terminal of positive polarity.
When first connected, the resistance is low but rises as the dielectric forms.
What’s the main difference between NPN and PNP transistor. [4 marks]In NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to the emitter but in a PNP transistor positive voltage is given to the emitter to Collector.

Oluwamuyide Peter

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