TESTING A TRANSISTOR ON A DIGITAL METER

Testing a transistor with a Digital Meter must be done on the "DIODE" setting as a
digital meter does not deliver a current through the probes on some of the resistance
settings and will not produce an accurate reading.
The "DIODE" setting must be used for diodes and transistors. It should also be called a
"TRANSISTOR" setting.
TESTING AN unknown TRANSISTOR
The first thing you may want to do is test an unknown transistor for COLLECTOR, BASE
AND EMITTER. You also want to perform a test to find out if it is NPN or PNP.
That's what this test will provide.
You need a cheap multimeter called an ANALOGUE METER - a multimeter with a scale
and pointer (needle).
It will measure resistance values (normally used to test resistors) - (you can also test
other components) and Voltage and Current. We use the resistance settings. It may
have ranges such as "x10" "x100" "x1k" "x10"
Look at the resistance scale on the meter. It will be the top scale.
The scale starts at zero on the right and the high values are on the left. This is
opposite to all the other scales.
When the two probes are touched together, the needle swings FULL SCALE and reads
"ZERO." Adjust the pot on the side of the meter to make the pointer read 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.

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.

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.