Out-Of-Circuit Transistor Resistance Measurements; Ohmmeter Ranges For Transistor; Resistance Measurements - HP 415E Operating And Service Manual

Model 415Е
tion. Use the transistor symbol оп the schematic
diagram to determine the bias polarity required to
forward-bias the base-emitter junction. The A part
of Figure 5-4 shows transistor symbols withterminals
labelled. Notice that the emitter arrow points toward
the type N material. The other two columns of the
illustration compare the biasing required to cause con-
duction and cut-off in transistors and vacuum tubes.
If the transistor base-emmiter diode (junction) is
forward-biased the transistor conducts. Ifthe diode is
heavily forward-biased, the transistor saturates.
However, if the base-emitter diode is reverse-biased
the transistor is cut off (open). The voltage drop
асговв а forward-biased emitter-base diode varies
with transistor collector current. For example, а
germanium transistor has a typical forward-bias,
base-emitter voltage of 0.2-0.3 volts when collector
current is 1-10 ma, and 0.4-0.5 volts when collector
current is 10-100 ma. In contrast, forward-bias volt-
age for silicon transistors is about twice that for ger-
manium types: about 0.5-0.6 volts when collector eur-
rent is low, and about 0.8-0.9 volts when collector
current is high.
5-45. Figure 5-4, part B, shows simplified versions
ої the three basic transistor circuits and gives the
operating characteristics of each. When examining а
transistor stage, first determine if the emitter-base
diode is biased for conduction (forward-biased) by
measuring the voltage difference between emitter and
base. When using an electronic voltmeter, do not
measure directly between emitter andbase: there may
be sufficient loop current between the voltmeter leads
Table 5-4. Out-of-Circuit Transistor
Resistance Measurements
Section V
Paragraphs 5-38 to 5-47
to damage the transistor. Instead, measure each volt-
age separately with respect to a voltage common point
(e.g., chassis). If the emitter-base diode is forward-
biased, check for amplifier action by short-circuiting
base to emitter while observing collector voltage. Тһе
Short circuit eliminates base-emitter bias and should
cause the transistor to stop conducting (cut off). Col-
lector voltage should then. shift to near the supply volt-
age. Any difference is due to leakage current through
the transistor апа, ingeneral, the smaller this current,
the better the transistor. If collector voltage does not
change the transistor has either an emitter-collector
Short circuit or emitter-base open circuit.
5-46. OUT-OF-CIRCUIT TESTING.
5-47. The two common causes of transistor failure
are internal short- and open-circuits. Remove the
transistor from the circuit and use an ohmmeter to
measure internal resistance. See Table 5-4 for
measurement data.
CAUTION
Most ohmmeters сап supply enough current
or voltage to damage a transistor. Before
using an ohmmeter to measure transistor
forward or reverse resistance, check its
open-circuit voltage and short-circuit
current output ON THE RANGE TO BE
USED, Open-circuit voltage must not exceed
1.5 volts and short-circuit current. must be
less than 3 ma, See Table 5-5 for safe resis-
tance ranges for some common ohmmeters.
Table 5-5. Ohmmeter Ranges for Transistor
Resistance Measurements
02152-2
—
Safe Open | Short Lead
Connect Ohmmeter
Ohmmeter Range(s)
Ckt Ck СОР
Transistor Pos. Neg. Measure Voltage|Current| Color |Polarity
Type leadto | lead to ric ole hp 412A [R x 1K 1.0V | ima
(ohms) hp 427A |RX10K | LOV (100ра | вод
4 [ic exc P Ех 100К| 1.0У | 10ра +
emitter | base* 200-250 Rx1M 1.0V lua Black -
Small | Rx10M| 1.0V |0. Ipa
PNP Signal | emitter | collector | 10K-100K
Ger
hp 410C IR x ІК
1.3V |0.57 ma
де emitter | base* 30-50 Rx10K | 1.3У | 57џа
manium | power Rx 100K) 1.3V |5.Тра ШЕ *
emitter | collector | several Rx1M | L3V |0.5pa
hundred Rx 10M) 1.3V |0.05ua
hp 410B R x 100 1.1V 1.1 ma
base
emitter
iK-3K
R
Rx1K
1.1V |110ша
Small ; Black +
Ыы т Rx10K | 1.1V | Lipa
Signal very high Rx100K| L1V |1.1ра | 9) 7
collector | emitter | (might Rx1M 1.1V |0. Lipa
read open)
NPN Simpson |R x 100 1.5V lma | Red *
Silicon base emitter | 200-1000 260 Black| -
Simpson |R x 1K 1.5V |0.82 Black
Power
high,
often
269 Š
г
T Red
:
collector |ешійег | greater 7
than 1M Triplett |В x 100 1.59 |3.25 ma ү А
Varies with
630 R x IK 1.5V |325pa Serial
*To test for transistor action, add collector-base Triplett |R x 10 1.5V |750на Number
Short. Measured resistance should decrease. 310 Rx100 | 1.5У | Тбра
—L
5-11