the FUNCTION switch to the XSTR-VIS mode.
IN-CIRCUIT TESTING. --When testing
The amber light should flash at about a l-second
diodes in-circuit, attach the emitter lead to the
rate. Insert the transistor under test in the proper
anode of the diode. Attach the collector lead to
socket.
the cathode. When testing transistors, attach the
In this mode, you perform two tests on the
leads to the right terminals as shown by the
transistor. The amber light shows the performance
schematic. If the operator happens to fasten the
of each test. When the amber light is out, this is
leads to the transistor in the wrong order, an
the EB-BC test mode. When the amber light is
erroneous display will result. However, if the
on, this is the emitter-collector test mode. The test
transistor is good, the instrument will give a good
shows good transistors by one pair of similarly
indication. The indication will be for the transistor
colored lights (green for NPN and red for PNP)
of the opposite type. A good NPN improperly
when the amber light is off. When the amber light
connected will give good PNP indications and vice
is on, no lights show good transistors. The left-
versa. If the device is bad, the instrument will give
hand lights show the condition of the emitter-base.
a bad indication. You cannot make a qualitative
The right-hand lights show the condition of the
analysis of the kind of failure unless you attach
base-collector. The absence of one or all lights in
the proper leads to the correct terminals.
the EB-BC test mode shows an open or opens.
To ensure the instrument will show the correct
The occurrence of both a red and a green light
type of transistor (PNP or NPN), you must
on either side in the EB-BC test mode shows a
identify the base lead. Use the following procedure
short.
to identify the base lead:
For more information about the Model 900
tracker, refer to Maintenance Manual, All Levels
1. Disconnect the lead to the emitter terminal
for Automatic Transistor Analyzer Model 900,
on the instrument. Only the light repre-
ST810-AD-0PI-010, for patterns other than those
senting the emitter junction should go out.
just discussed. There are 96 possible patterns
2. Reconnect the emitter lead.
listed.
3. Disconnect the lead to the collector
terminal of the instrument. Only the light
VIS MODE: DIODE. --You can not properly
representing the collector junction should
test diodes in the XSTER mode. To test a diode,
go out.
insert the diode in the proper socket and turn the
4. Should both lights go out during the tests,
FUNCTION switch to the DIODE/VIS mode. If
the connections are incorrect.
the diode is good, a pair of green lights will flash
5. Rearrange the leads on the transistor and
out of phase with the amber. If a pair of red lights
perform-the tests again. You should now
flash out of phase with the amber light, the
see the proper results.
diode is either installed improperly or marked
improperly. If the diode has a short, additional
There are six possible combinations for the
lights will flash out of phase with the amber. No
c o n n e c t i o n of these leads. Four of these
lights will flash in phase with the amber.
combinations are incorrect. These will cause the
You cannot properly test transistors in the
instrument to give an incorrect indication as to
DIODE mode. When testing transistors, only one
transistor type (PNP or NPN). The other two
transistor should be in the test socket at one time.
combinations will give proper indications, but you
Do not leave any diodes in the diode socket while
still may not know which leads are the emitter and
testing transistors. When testing diodes, do not
collector terminals. You will know whether the
leave transistors in the transistor sockets. If you
transistor is good, and whether it is an NPN or
do not observe these precautions and the devices
PNP transistor. If you must know which leads
left in the socket are defective, incorrect light
are the emitter and collector terminals, it is
indications will occur. These indications may
possible to find out after identifying the base lead
mislead the operator into believing the device
using the meter mode for Beta.
under test is defective.
SND Mode. --In either the XSTR/SND mode
WARNING
or DIODE/SND mode, light patterns showing
Unit being tested must be disconnected
good devices will have an accompanying beeping
sound from the Sonalert TM. The beeping will be
from ac outlet, and all capacitors capable
of storing electricity y should be discharged.
out of phase with the amber light.
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