Velleman DCA55 - Manual (Page 14)

Atlas DCA User Guide October 2007 – Rev 7
Page 14
Faulty or Very Low Gain Transistors
Faulty transistors that exhibit very low gain
may cause the Atlas DCA to only identify one
or more diode junctions within the device. This
is because NPN transistors consist of a
structure of junctions that behave like a
common anode diode network. PNP transistors
can appear to be common cathode diode
networks. The common junction represents the base terminal. This is normal
for situations where the current gain is
so low that it is immeasurable at the test
currents used by the Atlas DCA.
Please note that the equivalent diode pattern may not be correctly
identified by the Atlas DCA if your transistor has additional diode(s)
in it’s package (such as a collector-emitter protection diode). This is
due to multiple pn junctions that cannot be uniquely analysed.
In some circumstances, the unit may not be able to deduce anything sensible
from the device at all, in which case you will see either of these messages:
B
C
E
Common anode
diode network
Unknown/Faulty
component
No component
detected