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How to Test an Unknown Transistor


This is an old question how to test an unknown transistor but its imported for electronic world. The first thing you can do is check for an unknown transistor collector, base and emitter. You also need to know if it is NPN or PNP.

You need a cheap multimeter called analog meter - Multimeter with the price and the pointer (arrow).
It will measure the resistance value (usually used for testing resistors) - (you can also check other components) and the voltage and current. We use the impedance setting. This may range, such as "x10" "x100" "X1K" "x10" Look at the scale of resistance per meter. This is the top scale.

The scale starts at zero and high values ​​of the right to the left. This is the opposite of all the other scales. .
When two probes are touched together, the needle swings full scale and reads "ZERO". Adjust the pot on the side of the counter to make the read pointer is exactly zero.

 How to read:  "x10"  "x100"   "x1k"   "x10"

Up-scale from the zero mark is "1"
When the needle swings to this position on the "x10" setting, the value is 10 ohms.
When the needle swings to "1" on the "x100" setting, the value is 100 ohms.
When the needle swings to "1" on the "x1k" setting, the value is 1,000 ohms = 1k.
When the needle swings to "1" on the "x10k" setting, the value is 10,000 ohms = 10k.
Use this to work out all the other values on the scale.

Resistance values get very close-together (and very inaccurate) at the high end of the scale. [This is just a point to note and does not affect testing a transistor.]

Step 1   - FINDING THE BASE  and determining NPN or PNP

Get an unknown transistor and test it with a multimeter set to "x10"
Try the 6 combinations and when you have the black probe on a pin and the red probe touches the other pins and the meter swings nearly full scale, you have an NPN transistor. The black probe is BASE
If the red probe touches a pin and the black probe produces a swing on the other two pins, you have a PNP transistor. The red probe is BASE If the needle swings FULL SCALE or if it swings for more than 2 readings, the transistor is FAULTY.

How to Test an Unknown Transistor


Step 2   - FINDING THE COLLECTOR and EMITTER

Set the meter to "x10k."
For an NPN transistor, place the leads on the transistor and when you press hard on the two leads shown in the diagram below, the needle will swing almost full scale.

How to Test an Unknown Transistor

How to Test an Unknown Transistor


For a PNP transistor, set the meter to "x10k"  place the leads on the transistor and when you press hard on the two leads shown in the diagram below, the needle will swing almost full scale.

How to Test an Unknown Transistor

How to Test an Unknown Transistor



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