How to test a transistor with DMM?

A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor’s terminals changes the current flowing through another pair of terminals.
Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.

All Type Transistor Base leads view & smd type

PNP-BC557-datasheet
NPN-BC547-datasheet
NPN Transistor TESTING By Digital multimeter.

SELECT DIODE MODE DIGITAL MULTIMETER.
Forward bias:

Step 1.

• Connect DMM (+) Test Red lead    to Base
• ………….DMM ( -) Test Black lead to Collector =display shows the reading = 0.615v
•  ………….DMM  (-) Test Black lead to Emitter  = 0.645v

Verification:  If the DMM reading is from 0.641v to 0.645v the condition is GOOD.

Reverse bias:

Step 2.

• Connect DMM (-) Test lead to BASE
•  ………….DMM (+)Test lead  to Collector reading shows = OL or ‘1’ or  OPEN
•  ………….DMM (+)Test lead  to Emitter     = OL or ‘1’ or open.

Verification:   If the DMM reading is OL the condition is GOOD CONDITION.

Step 3.

• DMM  (+) Test lead to collector
•  DMM  (-) Test  lead to Emitter.

DMM Reading shows = OL  or ‘1’ or open (overload) the condition is  GOOD

 Step 4.

• DMM  (-) Test lead to collector
• DMM  (+) Test  lead to Emitter

DMM Reading shows = OL  or ‘1’ or open (overload) the condition is  GOOD.
Verification: If you get reading in forward bias as 0000 or ‘OL’  or ‘1’ or open  and  in reverse bias as 0000 (or) low values the transistor can be FAULTY and needs replacement.

HOW TO TEST POWER TRANSISTOR?

Transistor BU 208 or 2N3055 Testing

Forward bias:   Connect DMM (+) Test Red lead  to Base
DMM (-) Test Black lead to Collector reading shows = 0.449v
DMM (-)  Test Lead to Emitter    = 0.502v
Verification: If the DMM reading is from 0.502v to 0.449v the condition is GOOD.

Reverse bias:

Connect DMM (-) Test lead to BASE
DMM (+ )Test lead  to Collector reading is = OL or 1 or open
DMM (+ )Test lead  to Emitter    = OL or 1 or open
DMM Reading shows = OL (over load) the condition is GOOD

Verification:  If you get reading in forward bias as 0000 or OL  or 1 or open and in reverse bias as 0000 (or) low values the the transistor can be FAULTY and needs replacement.

  TEST YOUR TRANSISTOR BY BELOW CIRCUIT (SL-100 TYPE)

Transistor Test Circuit:-

Required components are: R1k,Rl-470E, Tr SL-100, Toggle switch-1.,  Connect a LED in  series with collector RL (load resistor) the LED.

Step-1.
When the switch is open the LED condition is OFF.
Close switch sw1 to base now LED condition is ON.