Atlas DCA User Guide September 2014 – Rev 11
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 is a darlington type or
has additional diode(s) in its 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
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