Heathkit IT -3120 User Manual

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DIODE TESTING
NOTE: Some high voltage diodes, those that have more than
a 1.5 volt drop across the ju nction when the diode is
conducting, cannot be adequately tested.
Drawings G and H of Figure 3 show the schematic symbols
for diodes.
The following
diode tests measure the forward (conducting)
current and the reverse (leakage) current. Like transistors,
the leakage current depends on the diode type (silicon or
germanium). Silicon diodes have very little leakage, while
germanium
diodes may have as much as several
microamperes leakage
current.
A good signal diode will have a forward current greater than
0.8 mA, while a good power diode (rectifier) will have a
forward
current greater than 0.8 A.
The actual zener voltage of a zener diode cannot be tested.
However, if a zener diode tests good as a conventional diode,
you can assume that it is good. Always test zener diodes and
varactor diodes in the same manner as signal diodes. Some
temperature compensated zener diodes cannot be tested.
The following procedure pertains to both in-circuit and
out-of ·circuit testing. If you do not obtain the proper results
when a diode is tested in- circuit, remove it from the circu·it
and repeat the tests.
1.
Be sure the ON-OFF switch is in the OF F (out)
position.
2. Identify the diode leads.
3. Connect the cathode 'lead of the diode to the C
connector (brack) of the Tester.
4.
Connect the anode lead of the diode to the E
connector (red) of the Tester.
5.
Press the TRANS switch.
6.
Press the 100 JJA switch.
7.
Press the Iceo switch.
8. Be sure the NPN·PNP switch is in the NPN (out)
position.
9.
Press the ON-OFF switch to the ON (in) position .
Read
the leakage current directly from the leakage
scale. This leakage should be
fess than a few
microamperes.
10 . Press the NPN-PNP switch to the PNP (in) p osition.
CAUTION : In the following steps, do not select a current
range that exceeds the current rating of the diode.
11. If a signal diode is being tested, press the 1 mA switch.
If a power diode (rectifier) is being tested, press the
1 A switch. The meter indication should be greater
than 80 on the leakage scale for both types of diodes .
12. Release
the ON-OFF switch to the OFF (out)
position.
13 . Disconnect the diode from the Tester.
UJT TESTING
Drawings J and K of F igu re 3 show the schematic symbols
for both the N channel and the P channel (uncommon)
UJT's (unijunction transistors).
Three measurements (leb
2
s, Ib
2
b I s, and Ib
2
es) will be made
in the following steps.
Ieb
2
s is the measurement of leakage current ([) between the
emitter (e) and base 2 (b
2
)
with base 1 shorted (s) to base 2.
Ib
2
b I S is the measurement of forward current (I) through
base 2 (b
2
)
and base 1 (b I ) with the emitter shorted (s) to
base 1. This current can be converted to Rbb (the resistance
between base 1 and base 2) as follows :
1.5
V (battery voltage) = Rbb
Ib
2
b IS
Ib
2
es is the measurement of emitter current (I) between
base 2 (b
2
)
and the emitter (e) with base 1 shorted (s) to the
emitter.
Because only leakages are measured, unijunction trans i stors
must be tested out-of-circuit . This will eliminate erroneous
leakage indications caused by circuit resistances.
1.
Be sure the ON- OFF switch is in the OFF (out)
pos i tion.

Heathkit IT -3120 Specifications

General

Brand	Heathkit
Model	IT -3120
Category	Test Equipment
Language	English