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Maintenance; Introduction; Test Equipment; Assembly Identification - HP AM-4380/U 5261A Technical Manual

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5-1.

INTRODUCTION.

5-2.
This section of the manual provides maintenance
and service information for the Model 5261A Video
Amplifier.
Included are troubleshooting procedures, a
table
of
recommended
information, and in-cabinet performance checks which
may be used to verify proper operation of the instrument.
5-3.

TEST EQUIPMENT.

5-4.
Recommended test equipment for checking
performance and troubleshooting is listed in Table 5-1.
Test instruments not listed that have specifications equal
to or better than the required characteristics listed may
be used.
5-5.

ASSEMBLY IDENTIFICATION.

5-6.
Throughout
this
assemblies are referred to by assembly number. For
example, the Video Amplifier Assembly is referred to as
A3. Connections to pins of the 50-pin plug on the rear of
the instrument are referred to by the plug number and pin
number; for example, pin 1 is referred to as P6(1).
5-7.

IN-CABINET PERFORMANCE CHECK.

5-8.
The performance
verify proper operation of circuits in the Video Amplifier
and may be used:
a. as part of an incoming inspection check of
instrument specifications;
b. periodically, for instruments in systems
where maximum reliability is of primary importance;
c. as part of a troubleshooting procedure to
locate malfunctioning circuits, and
d.
after any repairs or adjustments, before
returning instrument to regular service.
5-9.

ADJUSTMENTS.

5-10.
HIGH
FREQUENCY
ADJUSTMENTS A3C4, A3Cll.
5-11.
Trimmer capacitors A3C4 and A3Cll in video
amplifier assembly A3 provide the only adjustments for
frequency response. Adjust these capacitors only when
the bandwidth check (Table 5-2, In-Cabinet Performance
Checks)indicates the frequency response is outside the
±3 db limits. The access hole for tuning A3C4 is on the
bottom of the instrument and A3Cll access hole is on the
left side.
Use a plastic tuning wand for adjustments.
Adjust
A3C4
and
test
equipment,
repair
manual,
printed
circuit
checks listed in Table 5-2
RESPONSE

A3Cll

as
follows
SECTION V

MAINTENANCE

a.
counter by loosening lock screws and sliding unit out of
counter plug-in compartment.
b.
Video Amplifier rear plug to counter lack inside plug-ln
compartment.
c. Set counter controls as follows:
SAMPLE RATE............. slightly cw out oA POW'ER OFF
SENSITIVITY................ PLUG-IN
TIME BASE................... 1 MS
FUNCTION ................... FREQUENCY
d.
e.
through (hp)10100A feed through termination to 50 Ω
OUTPUT.
f.
(hp)10100A feedthrough termination to Video Amplifier
INPUT. Set frequency to 1000 kc and adjust output level
for 150 mv indication on voltmeter (use -3 db mark as
reference).
g.
500 kc to 60 Mc. If voltmeter indicates less than -6 db or
more than 0 db. adjust A3C11 to bring the voltmeter
indication within these limits.
h.
voltmeter indication is less than -6 db or more than 0db,
adjust A3C4.
i.
indication is within the limits for both steps.
j.
500 kc and 60 Mc. Observe that voltmeter indication
remains between -6 db and 0 db over this frequency
range.
5-12.

OUTPUT METER CALIBRATION.

5-13.
Meter Cal potentiometer A4R13 is located on
output amplifier assembly A4 and is accessible from the
top when the Video Amplifier is outside the counter plug-
in compartment. Adjust A4R13 as follows:
a.
5-11, steps a, b, and c.
b.
the Video Amplifier INPUT. Set oscillator frequency to
100 kc.
c.
Amplifier 50 Ω OUTPUT through ; 10100A feedthrough
termination.
5-1
Paragraphs 5-1 to 5-13
Remove
Video
Amplifier
Use ', 10506B extension cable and connect
Set Video Amplifier SENSITIVITY to 3 MV.
Connect Model 411A RF Millivoltmeter
Connect Model GOGA generator through
Slowly change generator frequency from
Set generator frequency to 30 Mc and it
Repeat steps g and h until the voltmeter
Slowly change generator frequency between
Perform operations indicated in Paragraph
Connect Model 200CD oscillator output to
Connect Model 403B voltmeter to the Video
Model 5261A
Section V
plug-in
from

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