How to check transistor

 To check a transistor (NPN or PNP type) using a digital multimeter, follow the steps below. This method checks if the transistor is functioning properly by using the diode test mode of the multimeter.

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🛠 Tools Needed:

Digital Multimeter with Diode Test Mode

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🔍 Step-by-Step Guide:

Step 1: Identify the Transistor Terminals

For NPN/PNP Bipolar Junction Transistors (BJTs):

B = Base

C = Collector

E = Emitter

You can find the pinout in the transistor's datasheet or search the part number online.

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Step 2: Set Multimeter to Diode Mode

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✅ For NPN Transistor Testing:

(a) Test Base to Emitter

Connect Red probe to Base, Black probe to Emitter.

A good NPN transistor will show a voltage drop (0.6V to 0.7V).

(b) Test Base to Collector

Red to Base, Black to Collector.

Again, it should show 0.6V to 0.7V.

(c) Reverse the probes

Put Black on Base, Red on Emitter/Collector.

The multimeter should show OL or no reading.

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✅ For PNP Transistor Testing:

(a) Test Base to Emitter

Connect Black probe to Base, Red probe to Emitter.

You should get a voltage drop (0.6V to 0.7V).

(b) Test Base to Collector

Black to Base, Red to Collector.

Again, it should show 0.6V to 0.7V.

(c) Reverse the probes

Put Red on Base, Black on Emitter/Collector.

It should show OL (no conduction).

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Step 3: Check C-E Junction

Measure between Collector and Emitter both ways:

Should read OL or no conduction in both directions (in a good transistor).

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🔴 Fault Indications:

Reading Possible Fault

0V both directions Shorted junction

OL both directions Open junction

Conduction in C-E Leaky or shorted transistor

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📘 Diagram (Text-based):

NPN:          PNP:

B --|>|-- E    E --|<|-- B

B --|>|-- C    C --|<|-- B