Check of transistor

How do you measure whether a transistor are damaged/dead? What is it that
typically happens to a transistor, why does this happen and how do you
measure it?
I have read somewhere that shortcuts between some of the three pins could
occur, is this correct?

Best Regards
Don

 

There are three basic types of failures in electrioncs.
Open, shorted or leaky.
These are the most common problems in transistors
BUT are not the only ones, you can add the word "intermittantly" to the
front of each of those three
and still have others to learn.
The first thing to know when measuring is what to
expect as a measurement, that means knowing your
equipment and its use and knowing what is a good/bad measurement on what you
are measuring.
Not all transistors will check the same, not all
transistors that check good will be good, not all meters
read the same, in circuit tests are not perfect, out of
circuit tests are not perfect, sometimes leaky is OK.
The short answer to your first question is experience.
Jeff

 

Generally speaking though, a short circuit "Zero Ohms Resistance"
between any legs of a transistor
is a good indication that it has failed.

One has to know how to use the meter to do the test though, as
the results and method of doing so can vary for different meters and
give you a false impression of a good or bad transistor. Which is what
Jeff said.

Use a Multimeter with a diode checking function 'So that it can bias
the transistor". This will allow for reading the device in an active
state and should give rise to more accurate assessment of whether the
device is operational at all.
If it measures zero ohms in this test then it's a good chance that the
transistor is no good.
If it measures with some resistance "There may be a scale indicating
good or bad on the meter" showing a voltage potential of say .7volt
for a Silicon or Germanium type Transistor or .2 Volt for a FET,
shottky. These values can vary dramatically depending upon transistor
type. But it can give you a general idea of the transisitors
condition.
Swapping the + lead and - leads of the multimeter over will forward or
reverse bias the transistor under test "That's if the potential across
it is sufficient" and that's why I said to use a meter that has a
diode test function. Else it may indicate open circuit "High
resistance" in both directions, which can also give you an impression
that the transistor is faulty. Or it may infact be faulty.
Do these tests on a known good transistor first so that you know what
results to expect before checking other transistors that are unknown.

I hope this helps.