How to test Bipolar Transistors if you have an Analog Multimeter

Picture of How to test Bipolar Transistors if you have an Analog Multimeter
We know how transistor works but some of us doesn't really know how to test the component itself. Nowadays, most Digital Multimeters have sockets provided to test them, but what will you do if you have those old Analog/Needletype ones? This is a simple way to do it.
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Step 1: Basic Configuration

Picture of Basic Configuration
Bipolar transistors has 3 pins, The Emitter(E), Base (B) and the Collector (C) which is usually connected to the casing for most Power transistors (TO-3 casing). It can be categorized into two, NPN and PNP configuration, see figure 2. This test is based on the theory that a transistor is like two diodes connected together, see figure 1.

Step 2: For PNP Transistors

1. Set your Analog Multimeter to Ohmmeter X1 Ohm Scale.

2. Connect the Negative Probe (Black) to Emitter and the Positive Probe (Red) to the Base. The needle should deflect to the right side,reading less than 100 ohms.

3. Now invert the probe connections to the Emitter for the Red Probe and to the Base for Black. The Needle should not deflect.

  • If the results are the same as above, your Emitter-Base junction is OK.

4. Now we will be testing the Base-Collector junction. Connect the Red probe to the Base and the Black probe to the Collector. The Needle should deflect to the right, resistance usually is not less than 100 ohms.

5. Invert the probes again, Black to the Base and the Red probe to the Collector. The Needle should not move.

  • If results are the same as above, your Base-Collector junction is Ok.

6. Connect the probes to the Emitter and Collector (probes may be inverted), a reading above 1Kohms indicates a working transistor.
Tbus10 months ago

It's nice to see posts using analog meters. My instructor just posted an article on comparing using an analog vs digital multimeter when checking diodes if anybody is interested.

hchavez11 year ago
instruction #6 question... what if there is no reading from emitter and collector?

thank you sir..
baki226 years ago
hai all friend, I need capasitor tester, thanks
Phil B baki225 years ago
I once built a capacitor tester that used a 555 timer and various resistances for the different capacitance ranges. An LED lit up or not as an indicator. It worked pretty well. Do an Internet search for DIY capacitor tester and you will come up with a variety of ways to test capacitors.
here's hundreds of capacitor tester at eBay and Amazon; even tester that test the capacitor in the circuit, I will buy one of these because I fix electronics and I have to test capacitors and is a pain unsoldering capacitors just to test them. Is much better than to build your own;don't forget that if you build your own, what are you doing is gaining a lot of more experience on how a electronic device work,only experience,will never be the same as to buy one which is built by electronic companies with a up to date equipment very sophisticated equipment.
omnibot baki225 years ago
Buy a modern digital multimeter, they usually have it built in.
Wulf8 years ago
Good article to diagnose transistor issue, in fact I've replaced two burnt transistor in the 19" LCD monitor's (that I got for free) power supply. $1.15 worth of replacement transistors is all it took to get the $300 monitor's backlight working again.
omnibot Wulf6 years ago
That must be good for value as well as environment. Good job.
Talking Electronics (author)  Wulf8 years ago
Good for You, thats pure savings i should say
royalestel8 years ago
Hey thanks!--I was just wondering how to figure out if a transistor I had was NPN or PNP.
Talking Electronics (author)  royalestel8 years ago
Your Welcome