HP 4328A Service Manual

F
I
!
~·
I
i
~·
Model 4328A
d.
ALL ranges should be checked with Standard
Resistors and adjusted if necessary. A4R101 *,
102*, 109*, 110*, 111*, and 117* through 122~'
are all factory selected.
e. Set the range to 1000 and measure an impedance
of (R + jwL) as shown in Figure 5-3, where R
should be calibrated by DC bridge and the re-
actance value twice that of R.
f. A~ust C202 as the error should come within
±1 •O relative to the calibrated value (Note: C202
takes value from 0. 015 - 0. 025 tJF).
g. Check again at 1mn range whether the error is
in the above specification.
5-39. ISOLATING TROUBLE IN TRANSISTOR
CIRCUITS
5-40. General. The following information should
help determine is a transistor works. There are tests
for both in-circuit and out-of-circuit transistors,
which help to determine If a particular trouble is due
to a faulty transistor or some other component. See
Figure 5-l.
5-41. In-Circuit Testing. Intransistor circuit test-
ing the most important consideration is the transistor
base-emitter junction. Like the control gndof a vac-
uum tube, this is the control point in the transistor.
5-42. To check atransistor, first seeif the emitter-
base dwde is forward-biased by measuring the voltage
difference between emitter and base. When usmg an
electronic voltmeter, do not measure directly between
emitter and base; there may be sufficient loop current
between the voltmeter lead to damage the transistor.
Instead, measure each voltage separately with respect
to a voltage common point (e. g. , chassis).
5-43. If the transistor base-emitter Junction is
forward-biased, the transistor conducts. If the diode
is heavily forward-biased, the transistor saturates.
However, if the base-emitter diode ts reverse-biased,
the transistor is cut off (open). The voltage drop ac-
ross a forward-biased emitter-base junction varies
with transistor collector current. A germanium tran-
sistor has a typical base -emitter voltage of 0. 2 - 0. 3
volt with 1 - lOrnA collector current, and 0. 4 - 0. 5
volt with 10 - 100mA collector current. In contrast,
base-emitter voltage for silicon transistors is about
twtce that for germamum types; about 0. 5 - 0. 6 volt
for low collector current, and about 0. 8 - 0. 9 for high
collector current.
5-44. If the emitter-base Junctions forward-biased,
check for amplifier action by short-circuiting base
to emitter while observing collector voltage. The
transistor should stop conduction (cut off, which
should shift the collector voltage close to the supply
voltage. Any difference is due to current leakage
through the transistor. In general, the smaller the
current, the better the transistor. If collector volt-
age does not change, the transistor has either an
emitter-collector short circuit or emitter-base open
circuit.
Section V
Paragraphs 5 -39 to 5-52
5-45. OUT-OF-CIRCUIT TESTING
5-46. 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 5-5 for meas-
urement data.
5-47. COMPONENT REPLACEMENT IN ETCHED
CIRCUITS
5-48. GeneraL Etched circuit boards are sensitive
to heat and to scratches with sharp objects. This is
because the conductors are plated on to the circuit
boards and the plating extends through the component
mounting holes. Whenever possible, avoid unneces-
sary component substitution; it can damage the circuit
board and adjacent components.. See Table 5-7 for
recommended tools and materials.
5-49. AXIAL-LEAD COMPONENTS
5-50, Resistors, tubular capacitors and other axial
lead components can be replaced without unsoldering.
Cutthe componentleads near the bodyof the defective
component, remove the component and straighten the
leads left in the board. Wrap leads of the replacement
component one turn around the original leads, solder
the connection, and clip off the excess lead.
5-51 .. OTHER COMPONENTS
5-52. Replace other components as follo'Ys:
a. Remove defective component from circuit board.
Use a low-power soldering ironbecause exces-
sive heat may lift a conductor or damage the
board.
b. Remove solder from mounting holes with a sue-
tion device or a wooden toothpick. DO NOT USE
A SHARP METAL OBJECT SUCH AS AN
AWLORTWIST DRlLL. SHARP OBJECTS MAY
DAMAGE THE PLATED-THROUGH CONDUC-
TOR.
c. Shape the leads of the replacement component to
match the mounting-hole spacing.
d. Insert the component leads in the mounting holes
and position it as the original was. DO NOT
FORCE LEADS OF REPLACEMENT COMPO-
NENT INTO MOUNTING HOLES. A sharp edge
on the lead rna y damage the plated -through con-
ductor.
e. Solder the component in place andre move excess
flux from the soldered areas. Apply a protective
coating to prevent contamination and corrosion.
See Table 5-7 for recommendations.
5-5

HP 4328A Specifications

General

Brand	HP
Model	4328A
Category	Measuring Instruments
Language	English