Section VIII
TM 11-6625-2781-14&P-2
Table 8-3. Ohmmeters Used for Transistor Testing.
Table 8-2. Out-of-Circuit Transistor Testing.
Connect Ohmmeter
Open
Short
Lead
Measure
Ohmmeter
Range(s)
Circuit
Circuit
Color Pol
Transistor
Pos.
Neg.
Resistance
Voltage
Voltage
arity
Type
lead to
lead to
(ohms)
HP 412A
R x 1K
1.0V
1 mA
100A
Small
emitter
base*
200-250
HP 427A
R x 10K
1.0V
PNP
Signal
10A
R x 100K
1.0V
Red
+
Germ-
emitter
collector
10K-100K
1A
R x 1M
1.0V
Black
-
anium
emitter
base*
30-50
0.1,A
R x 10M
1.0V
Power
HP 410C
R x 1K
1.3V
0.57mA
emitter
collector
several
57 A
R x 10K
1.3V
hundred
5.7A
R x 100K
1.3V
Red
+
emitter
base*
10K-100K
0.5A
R x 1M
1.3V
Black
-
PNP
Small
0.05A
R x 10M
1.3V
Silicon
Signal
very high
HP 410B
R x 100
1.1V
1.1 mA
emitter
collector
(might
110A
R x 1K
1.1V
read open)
11A
Rx 10K
1.1V
Black
+
1.1,A
base
emitter
1K-3K
Rx 100K
1.1V
Red
-
Small
0.11 A
Rx 1M
1.1V
Signal
very high
Simpson
Rx 100
1.5V
1 mA
Red
+
collector
emitter
(might
260
read open)
Simpson
R x 1K
1.5V
0.82mA
Black
+
NPN
269
Red
-
Silicon
base
emitter
200-1000
Triplett
R x 100
1.5V
3.25mA
high, often
325A
630
Rx 1K
1.5V
Varies
Power
collector
emitter
greater
with
than 1M
Serial
750 A
Triplett
R x 10
1.5V
Number
*To test for transistor action, add collector-base short.
75A
310
Rx 100
1.5V
Measured resistance should decrease.
8-19. Transistor Out-of-Circuit Testing . Measuring
large collector-to-emitter current. Typical NPN transistor
the elements of a transistor will reveal the presence of
and PNP transistor operation is shown in Figure 8-3,
internal shorts or open circuits. See Table 8-2 for
part B; indicated current represents conventional flow of
measurement data and Figure 8-4 for examples of diode
positive charges external to the transistor and is not
and transistor marking methods.
intended to indicate flow of carriers inside the transistor
CAUTION
structure. Notice that the effect of emitter-base-collector
Most ohmmeters can supply enough
voltages is reversed between NPN and PNP transistors;
current or voltage to damage a
circuits which are arranged for an NPN transistor usually
transistor. Before using an ohmmeter
function normally for a PNP transistor if supply voltages
to measure transistor forward or
are reversed.
reverse resistance, check its open-
circuit voltage and short-circuit
amplifier configurations (Figure 8-3, part A). These
current output ON THE RANGE TO
amplifiers may be used alone or in combination to form
BE USED. Open-circuit voltage must
complex circuits.
not exceed 1.5 volts and short-circuit
current must be less than 3 mA. See
8-22. BASIC TRANSISTOR CIRCUITS
Table 8-3 for safe resistance ranges
8-23. Trigger Circuit. The trigger circuit (Figure 8-5,
for some common ohmmeters.
Schematic A) is a limiter or squaring circuit which
8-20. Transistor Biasing and Conduction . In a
transistor a small base-to-emitter current controls a
8-4
