How to Read Transistors on a Circuit Board

Transistors come in different styles, and all differ; the most common two types are PNP and NPN. The circuit board labels the emitter, collector and base; also known as the ECB. After you know how to read the transistors on the circuit board, then you will be able to test them using your electronic testing equipment.

Difficulty: Easy

Instructions

1. Look at the circuit board for the marking that is near the transistor. The marking may also be underneath the transistor.

2. 
    
   from http://www.elexp.com/t_test.htm

   Notice the arrows with a line at the point of the triangle and a line connecting them. You will also see a line coming out of the side of the connecting line.

3. Position the circuit board so that the line coming out is facing the left.

4. Look at the top triangle. If this triangle is pointing up, then it is the collector for a NPN transistor. If the triangle is pointing down, then it is the collector for a PNP.

5. Observe the bottom triangle. If the triangle is pointing down, then this is the emitter for a NPN transistor. If the triangle is pointing up, then it is the emitter for a PNP transistor.
   The line that is coming out to the left is always the base. If you lack this line and have a transistor with a metal housing, then the metal housing acts as the base.

References

• Testing diodes and transistors