HP AM-4380/U 5261A User manual

TM 11-6625-2906-1 4&P
TECHNICAL MANUAL
OPERATOR’S, ORGANIZATIONAL,
DIRECT SUPPORT AND GENERAL SUPPORT
MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS
AND SPECIAL TOOLS LIST)
FOR
VIDEO AMPLIFIER AM-4380/U
(HEWLETT-PACKARD MODEL 5261A)
(NSN 6625-00-269-4593)
HEADQUARTERS, DEPARTMENT OF THE ARMY
8 OCTOBER 1980

A

This manual Includes copyright material reproduced by permission of the HEWLETT-PACKARD Company
TM 11-6625-2906-14&P
TECHNICAL MANUAL HEADQUARTERS
DEPARTMENT OF THE ARMY
NO. 11-6625-2906-14&P}Washington, DC, 8 October 1980
OPERATOR’S, ORGANIZATIONAL, DIRECT SUPPORT AND
GENERAL SUPPORT MAINTENANCE MANUAL
(INCLUDING REPAIR PARTS AND SPECIAL TOOLS LISTS)
FOR
VIDEO MIPLIFIER ,MI-4380/U
(HEWLETT - PACKARD)
MODEL 5261A
(NSN 6625-00-269-4595)
REPORTING OF ERRORS
You can improve this manual by recommending improvements using DA Form 2028-2 located in the back
of the manual. Simply tear out the self-addressed form, fill it out as shown on the sample, fold it where shown,
and drop it in the mail.
If there are no blank DA Forms 2028-2 in the back of your manual, use the standard DA Form 2028
(Recommended Changes to Publications and Blank Forms) and forward to Commander, US Army
Communications and Electronics Materiel Readiness Command, ATTN: DRSEL-ME--MQ, Fort Monmouth, NJ
07,03. In either case a reply will be forwarded direct to you.
SERIAL PREFIX: 1124A
This manual applies directly to HP Model 5261A
Video Amplifiers having serial number prefix 1124A.
This manual Is an authentication of the manufacturer’s commercial literature which. through usage, has been found to
cover the data required to operate and maintain this equipment. Since the manual was not prepared In accordance with
military specifications and AR 310-3, the format TV not ban structured to consider levels of maintenance.
i

Model 5261 A
TABLE OF CONTENTS
Section Page
00-1. Scope............................................ 0-1
0-2. Indexes of Publications................. 0-1
0-3. Forms and Records....................... 0-1
0-4. Reporting Equipment Improve-
ment Recommendations (EIR)..... 0-1
0-5. Administrative Storage................. 0-1
0-6. Destruction of Army
Electronics Materiel..................... 0-1
IGENERAL INFORNIATION....................1-1
1-1.Introduction....................................1-1
1-2.Description.....................................1-1
1-4.Instrument Identification................1-1
1-6.Accessory Supplied.......................1-1
1-8.Accessories Available....................1-1
II INSTALLATION.......................................2-1
2-1.Initial Inspection.............................2-1
2-3 Storage and Reshipment...............2-1
2-6.Installation......................................2-1
2-8.Cooling..........................................2-1
2-10.Power Requirement.......................2-1
2-12.Electrical Connections...................2-1
III OPERATION..........................................3-1
3-1.Model 5261A Controls...................3-1
3-3.Operating Procedure.....................3-1
3-5.Operation with Pulse Input Signals3-1
3-7.Operation with High Impedance....3-1
Probe........................................3-1
3-9.Video Amplifier Input Impedance...3-1
Section Page
IV PRINCIPLES OF OPERATION..............4-1
4-1. Introduction................................4-1
4-3. Preamplifier Assembly Al1.........4-1
4-5. Attenuator Switch Assembly A2 4-1
4-7. Video Amplifier Assembly A3....4-1
4-10. Output Amplifier Assembly A4...4-1
VMAINTENANCE......................................5-1
5-1. Introduction................................5-1
5-3. Test Equipment.........................5-1
5-5. Assembly Identification..............5-1
5-7. In-Cabinet Performance Check.5-1
5-9. Adjustments...............................5-1
5-10. High Frequency Response
Adjustments A3C4. A3Cll.......5-1
5-12. Output Meter Calibration . .5-1
5-14. Troubleshooting and Repair......5-3
5-15. Troubleshooting.........................5-3
5-17. Printed Circuit Component
Replacement...........................5-3
VI REPLACEABLE PARTS.........................6-3
6-1.Introduction.....................................6-4
6-4. Ordering Information.......................6-5
ii

Model 5261A
APPENDIXES
Page
APPENDIX A. References .......................................................................... A-1
B. Components of End Item List........................................................B-1
C. Additional Authorization List .........................................................(N/A)
D. aintenance Allocation Chart
Section I. troduction ....................................................................................D-1
II. Maintenance Allocation Chart...........................................................D-3
III. Tools and Test Equipment
Requirements ................................................................D-4
E. Manual Change Information...........................................................E-1
LIST OF ILLUSTRATIONS
Figure Page
1-1.Model 5261A.............................................................................................1-0
3-1.Input Impedance vs. Input Frequency .......................................................3-1
3-2.Controls .............................................................................................3-2
3-3.Frequency Measurement with Model 5261A..............................................3-3
5-1.Schematic Diagram Notes..........................................................................5-5
5-2.Top View, Component Location .........................................................5-6
5-3.Bottom View, Component Location .........................................................5-7
5-4.Video Amplifier Schematic Diagram.........................................................5-7
A-1. Top View, Component Location.........................................................E-3
A-2. Bottom View, Component Location......................................................E-4
A-3. Video Amplifier Schematic...................................................................E-5
A-4. Al Preamplifier, Component Location...................................................E-6
A-5. Video Amplifier Schematic...................................................................E-7
LIST OF TABLES
Table Page
1-1.Specifications.............................................................................................1-1
1-2.Accessories Available ......................................................................1-1
3-1.Frequency Resolution.................................................................................3-1
5-1.Recommended Test Equipment.................................................................5-0
5-2.In-Cabinet Performance Check..................................................................5-2
5-3.Troubleshooting..........................................................................................5-4
6-1.Reference Designation Index.....................................................................6-3
6-2.Replaceable Parts.......................................................................................6-5
6-3.Manufacturer’s Code List............................................................................6-7
iii

TM 11-6625-2906-14 & P
SECTION 0
INTRODUCTION
0-1. SCOPE.
a. This manual describes Video Amplifier AM-
4380/U (fig. 1-1) and provides maintenance
instructions. Throughout this manual, AM-
4380/U is referred to as the Hewlett-Packard
(HP) Model 5261A Video Amplifier.
0-2. INDEXES OF PUBLICATIONS.
a. DA Pam 310-4. Refer to the latest issue of
DA Pam 310-4 to determine whether there are new
editions, changes, or additional publications pertaining to
the equipment.
b. DA Pam 310-7. Refer to DA Pam 310-7 to
determine whether there are modification work orders
(MWO’s) pertaining to the equipment.
0-3. FORMS AND RECORDS.
a. Reports of Maintenance and Unsatisfactory
Equipment.
Maintenance forms, records, and reports
which are to be used by maintenance personnel at all
maintenance levels are listed in and prescribed by TM
38-750.
b. Report of Packaging and Handling
Deficiencies.
Fill out and forward DD Form 6
(Packaging Improvement Report) as prescribed in AR
70058/NAVSUPINST 4030.29/AFR 71-13/MCO
P4030.29A and DLAR 4145.8.
c. Discrepancy in Shipment Report (DISREP)
(SF 361).
Fill out and forward Discrepancy in Shipment
Report (DISREP) (SF 361) as prescribed in AR 55-
38/NAVSUPINST 4610.33B/AFR 7518/MCO P4610.19C
and DLAR 4500.15.
0-4. REPORTING EQUIPMENT IMPROVEMENT
RECOMMENDATIONS (EIR).
EIR’s will be prepared using SF 368 (Quality Deficiency
Report). Instructions for preparing EIR’s are provided in
TN) 38-750, the Army Maintenance Management
System. ElR’s should be mailed direct to Commander,
US Army Communication and Electronics Materiel
Readiness Command, ATTN: DRSEL-NIE-NIQ, Fort
Monmouth, NJ 07703. A reply will be furnished direct to
you.
0-5. ADMINISTRATIVE STORAGE.
Administrative storage of equipment issued to and used
by Army activities shall be in accordance with T%, 740-
90-1 and paragraph 2-8.
0-6. DESTRUCTION OF ARMY ELECTRONICS
MATERIEL.
Destruction of Army electronics materiel to prevent
enemy use shall be in accordance with TM 750-244-2.
0-1

Model 5261A
Section I
Figure 1-1
FIGURE 1-1. Model 5261A
1-0

Model 5261A
Section I
Paragraphs 1-1 to 1-9
SECTION I
GENERAL INFORMATION
1-1. INTRODUCTION.
1-2. DESCRIPTION.
1-3. The Hewlett-Packard Model 5261A Video
Amplifier is a plug-in unit which increases the sensitivity
of the Model 52431,, 52451I, and 5: 345A Electronic
Counters. The Model 5261A provides for measurement
of signals as low as 1 millivolt over the frequencyrange
of 10 cps to 20 Me (52431) or 50) Mc (52451,). The
input impedance is I megohm and maybe increased to
1(0 megohmsbyusing a 10: 1 divider probe (HP stock
no. I000: 3A) An output signal is available at the
OUTPITT 50-ohm connector for monitoring the Video
Amplifier output or for activating external instruments.
This signal is identical in frequencyand amplitude to the
amplified signal supplied to the counter input circuit.
1-4. INSTRUMENT II)ENTIFICATION.
1-5. Hewlett-Packard uses a two-section serial
number mounted on the rear panel. Earlier instruments
use an eight-digit serial number (000-00000). The first
three digits are a serial prefix number; the last five digits
refer to the specific instrument. Later instruments use a
nine-digit serial number (0000A00000).The first four
digits are the serial instrument. If the serial prefix on your
instrument does not appear on the title page of this
manual, there maybe differences between the manual
and your instrument. If there are differences, theywill
be described in a change sheet included with the manual.
1-6. ACCESSORY SUPPLIED.
1-7. A 50 ohm, low microphonic cable HP
10507fi001, with BNC connectors is supplied in the
package with the Model 5261A.
1-8. ACCESSORIES AVAILABLE.
1-9. Table 1-2 lists the accessories available for the
Model 5261ilA Video Amplifier.
TABLE 1-2. Accessories Available
Description HP Stock No.
10:1 divider probe, 10 pf shunt 10003A
600V max., dc to 40 Mc
50-ohm feed-through termination 10100A
50-conductor extender cable 10506C
Plug-in adapter (for use with 5345A) 10509A
prefix and the last five digits refer to the specific TABLE 1-1. Specifications*
BANDWIDTH: 50 OHM OUTTPUT:
10 cps to 50 Mc with 5245I,; 10 cps to 20 Mc Separate BNC front panel output for oscillo-
with 5243I,. scope monitoring or for driving external equip-
INPUT SENSITIVITY: ment; 50-ohm source impedance. On ampli-
1 mV to 300 mV rms. fier’s most sensitive attenuator range, 1 mV
rms at input results in at least 100 mV rms at
INPUT IMPEDANCE: auxiliary output into 50-ohm load. Maximum
Approximately I megohm, 15 pf shunt; undistorted output is 300 mV rms into 50-ohm
HP 10003A Probe increases impedance to 10 load.
megohms, 10 pf shunt.
ATTENUATOR RANGES: ACCESSORY FURNISHED:
1, 3, 10, :30, and 100 mV rms. HP 100I 3A 10:1 Probe, 10 pf shunt, 600 volts
maximum; HP 10100A 50-ohm Feed-thru
MAXIMUM INPUT Termination, 10506B Extender Cable, 10590A
100 volts dc, 5 volts rms (ranges: 1, 3, 10, Plug-In Adapter.
30, 100 mV).
MONITOR: WEIGHT:
Meter shows when the signal level is accept- Net 2 lbs (0,90 kg); shipping 8 lbs (3,8 kg).
able to the counter.
ACCURACY: POWER:
Retains accuracy of 5243L, 5245L, or 5345A Supplied by 5243I,, 5245L, or 5345A Electronic
Electronic Counters. Counters.
*When installed in the HP Model 5243L, 5245L, or 5345A Electronic Counters.
1-1/1-2

Model 5261A
Section II
Paragraphs 2-1 to 2-13
SECTION II
INSTALLATION
2-1. INITIAL INSPECTION.
2-2 As soon as the Model 5261A is received, verify
that the instrument is intact and as ordered. Inspect the
plug-in for any physical damage such as scratched panel,
broken knob, or bent connectors. If damage is found,
refer to the warranty page at the rear of this manual and
Paragraph 2-5 for shipping and repackaging instructions.
2-3. STORAGE AND RESHIPMENT.
2-4. ENVIRONMENT. Conditions during storage
and shipment should be limited as follows:
a. Maximum temperature 167-F (75°C).
b. Minimum temperature -40-F (-40°C).
2-5. PACKAGING. To protect your instrument
during shipment or storage, use the best packaging
methods available. Your Hewlett-Packard field office
can provide materials similar to those used for original
factory packaging. Contract packaging companies can
provide dependable custom packaging on short notice.
a. If possible. use the original container
designed for the instrument. Otherwise, use a strong
carton (350 lb/sq inch bursting strength) or wooden box
to house the instrument.
b. Wrap the instrument in heavy paper or
plastic before placing it in the shipping container.
c. Use plenty of packing material around all
sides of the instrument and protect the front panel with
cardboard strips.
d. Seal the package with strong tape or metal
bands. Mark with "Delicate Instrument."
e. Refer to the warranty page at the rear of this
manual and check with your Hewlett-Packard field office
for shipping instructions. All correspondence
should refer to an instrument by model number and the
full, eight-digit serial number.
2-6. INSTALLATION.
2-7. To install the Video Amplifier in the compartment
provided at the right side of the counter front panel,
proceed as follows:
a. Remove AC power from the counter by
rotating the SAMPLE RATE control lull counter
clockwise to POWER OFF.
b. Loosen locking screws on either side of the
plug-in compartment (or single locking screw on left side
by turning fully counterclockwise.
c. Remove blank filler panel Or plug-in unit
installed.
d. Slide the Model 5261A into the
compartment. Make certain the plug-in is properly
aligned and tighten the locking screws.
2-8. COOLING
2-9. Tile Video Amplifier plug-in unit is cooled by the
ventilation of the (hp) counter in which it is installed.
Refer to the Operating and Service Manual of the
Counter for cooling system maintenance instructions.
2-10. POWER REOUIREMENTS
2-11. All voltages required to operate the Model
5261A are supplied by the circuits of the (hp) counter in
which the plug-in is installed.
2-12. ELECTRICAL CONNECTIONS.
2-13. The INPUT terminal on the front panel of the
plug-in (see Figure 3-2) provides the only connection for
the input signal. The front-panel OUTPUT 50 Ω
connector supplies the Video Amplifier output for
monitoring or external equipment. All connections to
the counter are completed through the 50-pin jack at the
rear of the plug-in unit.
2-1/2-2

Model 5261A
Section III
Paragraphs 3-1 to 3-10
SECTION III
OPERATION
3-1. MOLEL 5261A CONTROLS.
3-2. Figure 3-2 indicates the functions of the
connectors, meter, and SENSITIVITYcontrol on the
Model 5261A front panel.
3-3. OPERATING PROCEDURE.
3-4. The Video Amplifier plug-in unit is ac-coupled but
does not change anyfunctions of the counter in which it
is installed. Using the plug-in, period, multi-period,
frequency,totalizing, and ratio measurements can be
performed with input signals as low as one millivolt. Since
the measurements can be made with or without the
Video Amplifier installed, onlyfrequencymeasurement is
illustrated in Figure 3 3. For other measurement
procedures, see the Operating and Service Manual for
your Electronic Counter. Table 3-1 lists the frequency
resolution for all settings of the counter TIME BASE
control (Figure 3-3, item 3).
TABLE 3-1. Frequency Resolution
INPUT FREQUENCY = 11.1223344 Mc
TIME BASE Counter Display
Setting and Resolution
1 µsno display
1 µs11. Mc
10 µs11.1 Mc
.1 ms 11.12 Mc
1 ms 11122. kc
10 ms 11122.3 kc
.1 s 11122.33 kc
1 s 11122. 334 kc
10 s 11122. 3344 kc
3-5. OPERATION WITH PULSE INPUT SIGNALS.
3-6. The Video Amplifier is designed to amplify
sinusoidal input signals. However, pulse input signals
can be amplified if the output signal is monitored to
ensure a satisfactoryoutput to the counter. Monitor the
signal at the OUTPUT 50Q connector with an
oscilloscope and set the Video Amplifier SENSITIVITY
control for a level which results in satisfactorycounter
operation. Because the output level meter is an
average-responding device, it will read low with a pulse
input signal. Do not use the meter as an output level
indicator when amplifying pulses.
FIGURE 3-1. Input Impedance vs Input Frequency
3-7. OPERATION WITH HIGH IMPEDANCE PROBE
3-8. The (hp) 10003A 10:1 divider probe can be used
with the Video Amplifier. The 10:1 divider probe serves
to decrease the effects of resistive loading on the
external circuit at low frequencies. When using the
probe, Video Amplifier sensitivityis decreased by1 10.
As a result the maximum sensitivityof the Video Amplifier
is 10 mv.
3-9. VIDEO AMPLIFIER INPUT IMPEDANCE.
3-10. As illustrated in Figure 3-1, Video Amplifier input
impedance decreases at higher frequencies.
This decrease is due to the capacitive loading effect of
the amplifier input Thus when a signal source of fixed
impedance is connected to the Video Amplifier INPUT, a
meter at the signal source will not indicate the correct
input level at the Video Amplifier. To avoid this error,
monitor the input level at the Video Amplifier input with an
RF Voltmeter such as the (hp) Model 411A to ensure a
satisfactoryinput level. The Video Amplifier input can
also be terminated in the signal source characteristic
impedance but at frequencies near 50 Mc capacitive
loading reduces the input impedance, the signal source
is no longer terminated in its characteristic impedance,
and a meter at the signal source is incorrect. Thus, the
simplest method of ensuring a satisfactoryinput to the
Video Amplifier is to monitor the signal level at the Video
Amplifier input.
3-1

Model 5261A
Section III
Figure 3-2
CONTROLS
1. INPUT signal connector: apply a 1-100 mv AC signal
between 10 cps and 20 Mc (5243L) or 10 cps and 50
Mc (5245L).
2. SENSITIVITY control: calibrated in millivolts, this
control determines the sensitivity of the Video
Amplifier and is adjusted to keep the signal output to
the Counter within limits acceptable to the Counter
input circuits as indicated on the OUTPUT LEVEL
meter.
3. OUTPUT LEVEL meter: meter monitors the level of
the Video Amplifier output to the Counter. When
meter indicates in green portion of scale, Video
Amplifier output to Counter is satisfactory.
4. OUTPUT 50 Ωconnector: when terminated in 50
ohms, the signal at this connector is identical in
frequency and amplitude to the Video Amplifier
output to the Counter.
05261-A-6
FIGURE 3-2. Controls
3-2

Model 5261A
Section III
Figure 3-2
1. Apply power to Counter and Video Amplifier by 5. Set Video Amplifier SENSITIVITY to 100 MV.
turning SAMPLE RATE control slightly clock-
wise from POWER OFF position. 6. Connect signal to be measured to INPUT con-
2. Set Counter SENSITIVITY to PLUG IN. nector on Video Amplifier. DO NOT EXCEED
5 V rms.
3. Set TIME BASE to 10 ms.*
4. Set FUNCTION to FREQUENCY. 7. Vary SENSITIVITY control until OUTPUT
LEVEL meter reads in green portion of scale.
*TIME BASE setting may vary depending upon de-
sired resolution of INPUT signal frequency (Table 8. Observe frequency of INPUT signal as displayed
3-1). by Counter.
05261-A-3
FIGURE 3-3. Frequency Measurement with Model 5261A
3-3/3-4

Model 5261A
Section IV
Paragraphs 4-1 to 4-15
SECTION IV
PRINCIPLES OF OPERATION
4-1. INTRODUCTION.
4-2. The four functional sections of the Model 5261A
are illustrated in Figure 5-4. The preamplifier, attenuator,
video amplifier, and output amplifier circuits are
combined to amplify AC signals as small as 1 millivolt
and provide a usable output level to the counter input
circuit. All dc voltages to operate the Model 5261A are
supplied from the counter in which the unit is installed.
These dc voltages are filtered by components on
Amplifier assembly A4, which includes a series regulator
in the 15-volt line.
4-3. PREAMPLIFIER ASSEMBLY A1.
4-4. The preamplifier circuit consists of a nuvistor
cathode follower driving an emitter follower to provide a
high impedance input and a low impedance output.
Diodes A1CR1 and A1CR2 limit input signal peaks and
prevent damage to A1Q1. Resistor A1R4 limits A1Q1
gate current during overload. Capacitors A1C2, A1C3,
A1C4, and A1C5 filter variations from the dc voltage
lines.
4-5. ATTENUATOR SWITCH ASSEMBLY A2.
4-6. Resistive attenuator A2 reduces the input signal
and establishes the overall gain of the Video Amplifier.
The amount of attenuation inserted is controlled by the
Video Amplifier SENSITIVITY switch. RC networks
A2C2, A2R10, and A219, A2C1 are selected to improve
frequency response.
4-7. VIDEO AMPLIFIER ASSEMBLY A3.
4-8. The video amplifier consists of two amplifiers
with three transistors each and feedback and drift
compensation for gain stability Feedback is provided by
the RC combination of A3R5, A3C4, A3R13, A3C1 and
transistors A3Q3,A3Q6 in the feedback loops of the two
amplifiers. Drift compensation is also accomplished with
the addition of A3Q3 and A3Q6. Positive feedback to
amplifier No. 2 from output amplifier A4Q4 increases
amplifier No. 2 gain at higher frequencies.
4-9. The addition of A3Q3 and A3Q6 in the feedback
loops of the two amplifiers provides three functions: 1)
act as negative feedback amplifiers to reduce the gain
which reduces any drift caused by temperature changes
in the two-stage amplifiers; 2) maintain the amplifier gain
at low frequencies; and 3) filter ripple on the -14 volt line,
in conjunction with A3C6 and A3C13.
4-10. OUTPUT AMPLIFIER ASSEMBLY A4.
4-11. Output amplifier assembly A4 consists of: 1)
output amplifier circuit, 2) meter circuit: 3) plus 20volt
filter; and 4) series regulator. These four circuits are
discussed in Paragraphs 4-12 through 4-15.
4-12. OUTPUT AMPLIFIER. Emitter follower A4Q4
provides the amplified input signal to the counter via rear
panel plug P6, pin 1. This same signal is supplied to
OUTPUT 509 jack J2 for monitoring with an oscilloscope
or application to other equipment. Positive feedback
from A4Q4 emitter to amplifier No. 2 in the video
amplifier assembly increases the video amplifier gain at
higher frequencies. Capacitors A4C9 and A4C10 are
connected in parallel to improve the overall frequency
response.
4-13. METER CIRCUIT The signal atA4Q4 emitter is
rectified by A4C R2 and A4C R3 and filtered by A4C12.
This dc is supplied to OUTPUT LEVEL meter M1.
Capacitors A4C11 and A4C13 are connected in parallel
to improve the frequency response of the meter circuit.
Meter Cal potentiometer A4R13 provides an adjustment
for calibrating the OUTPUT LEVEL meter(Paragraph 5-
12). Minus 15 volts is supplied to the meter circuit and
establishes a bias on diodes A4CR2, 3. This prevents
the meter indicating for very small output signals and
permits a meter indication in the green scale for ml
output signal greater than 100 millivolts. Diode A4CR4
acts to protect the meter during input signals greater than
100 mv. A4CR4 anode is clamped at about -1.5 volts,
which corresponds to approximately full scale. When
the rectified signal output exceeds this value, A4CR4
conducts and protects the meter.
4-14. PLUS 20 VOLT FILTER. Transistors A4Q1,
A4Q2, and associated components filter variations and
noise from the t 20-ivolt line. A voltage change at A4Q1
collector causes a change at A4Q2 base and A4Q2
changes conduction to oppose the variation. The
emitter-collector voltage drop across A4Q2 is
approximately 1 volt and the ,20 volts becomes t 19 volts
at the drain of FET A1Q1. Resistors A4R2 and A4R3
form a dc voltage divider to establish the quiescent
voltage at A4Q1 base. Capacitor A4C2 bypasses to
ground ac variations at A4Q1 base.
4-15. SERIES REGULATOR. Series regulator A4Q3
provides regulated -14 volts for the Model 5261Acircuits.
Breakdown diode A4CRI establishes a reference voltage
at A4Q3 base. When the -15 volts changes, A4Q3
senses this change through A4R4 and increases
conduction to oppose the change. Inductor A4L1
reduces high-frequency transients in the -14 volt
regulated output.
4-1

Model 5261A
Section V
Table 5-1
TABLE 5-1. Recommended Test Equipment
Instrument Type Required Use Instrument
Characteristics Recommended
Electronic Counter Provide power (hp) Model 5243L or
(hp) Model 5245L
DC Voltmeter 0 v to ±25v; Troubleshooting (hp) Model 412A
10 M Ωinput impedance;
1% accuracy
AC Voltmeter 1 mv to 500 mv; Troubleshooting (hp) Model 403B
10 cps to 1 Mc; Circuit adjustment
2% accuracy
RF Millivoltmeter 1 mv to 500 mv; Troubleshooting; (hp) Model 411A with
500 kc to 50 Mc: Circuit adjustment (hp) 11025A Probe
3% accuracy (formerly (hp) 411A-21E)
Oscillator 10 cps to 100 kc; Troubleshooting; (hp) Model 200CD
1 mv to 500 mv Circuit adjustment
High Frequency 100 kc to 50 Mc: Troubleshooting; (hp) Model 606A
Signal Generator 1 mv- to 500 mv Circuit adjustment
Oscilloscope 10 cps to 10 Mc; Troubleshooting; (hp) Model 175A with
5 mv/cm (hp) Model 1752A
Coaxial Cable Low Microphonics Troubleshooting:; (hp) 10507A
Circuit adjustment;
Operation
Extender Cable 50-pin connectors; Permits operation (hp) 10506B
straight-through outside of counter
connections
Feed-through BNC to BNC; Troubleshooting: (hp) 10100A
Termination 50ΩCircuit adjustment (2 required)
DC Power Supply 100 vdc Performance Check (hp) 711A
5-0

Model 5261A
Section V
Paragraphs 5-1 to 5-13
SECTION V
MAINTENANCE
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 test equipment, repair
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 manual, printed circuit
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 checks listed in Table 5-2
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 RESPONSE
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 A3Cll as follows
a. Remove Video Amplifier plug-in from
counter by loosening lock screws and sliding unit out of
counter plug-in compartment.
b. Use ', 10506B extension cable and connect
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. Set Video Amplifier SENSITIVITY to 3 MV.
e. Connect Model 411A RF Millivoltmeter
through (hp)10100A feed through termination to 50 Ω
OUTPUT.
f. Connect Model GOGA generator through
(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. Slowly change generator frequency from
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. Set generator frequency to 30 Mc and it
voltmeter indication is less than -6 db or more than 0db,
adjust A3C4.
i. Repeat steps g and h until the voltmeter
indication is within the limits for both steps.
j. Slowly change generator frequency between
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. Perform operations indicated in Paragraph
5-11, steps a, b, and c.
b. Connect Model 200CD oscillator output to
the Video Amplifier INPUT. Set oscillator frequency to
100 kc. c. Connect Model 403B voltmeter to the Video
Amplifier 50 ΩOUTPUT through ; 10100A feedthrough
termination.
5-1

Model 5261A
Section V
Table 5-2
TABLE 5-2. In-Cabinet Performance Checks
1.BANDWIDTH: 10 cps to 50 Mc
a. Set counter controls as follows:
SAMPLE RATE slightly clockwise out of POWER OFF
SENSITIVITY to PLUG-IN
TIME BASE to .1 MS
FUNCTION to FREQUENCY
b. Set Video Amplifier SENSITIVITY to 3 MV. Connect (hp) 10100A 50-ohm feedthrough terminations to INPUT
and OUTPUT
c Connect Model 200CD Oscillator output to Video Amplifier INPUT and Model 403B Voltmeter to 50 Ω
OUTPUT.
d. Adjust Oscillator frequency to 100 kc and for indication of 120 mv on Voltmeter (use -4 db line as reference).
e. Slowly change Oscillator frequency from 100kc to 10cps. Video Amplifier output level should remain between
- 7 db and -1 db limits.
f. Disconnect Model 200CD and connect Model 606A to Video Amplifier INPUT through the (hp)10100A
feedthrough termination. Disconnect Model 403B from OUTPUT and connect Model 411A RF Voltmeter.
g Set generator to 1000 kc and adjust output level for -4 db reference as in step d. Remove Voltmeter from
OUTPUT and connect to INPUT. Record input level for reference level.
h. Connect Voltmeter to 50 ΩOUTPUT and slowly change generator frequency from 1000 kc to 100 kc. Repeat
above 100 kc to 50 Mc. Connect Voltmeter to INPUT periodically to check reference level. Video Amplifier
output should remain between -7 db and -1 db limits.
2. INPUT SENSITIVITY. 1 mv to 300 mv rms.
a. Set Counter controls as in 1 a.
b. Set Video Amplifier SENSITIVITY to 1 MV
c. Connect (hp) 10100A feedthrough terminations to Video Amplifier INPUT and 50 ΩOUTPUT
d. Connect 200CD to INPUT and Model 403B Voltmeter to 50 ΩOUTPUT. Adjust Oscillator frequency to 100
kc and for indication of 100 mv on Voltmeter
e. Disconnect Voltmeter from 50 ΩOUTPUT and connect Oscilloscope to 50 ΩOUTPUT. Oscilloscope display
should be a sine wave with no clipping.
f. Connect Voltmeter to Oscillator output. Voltmeter should indicate less than 1 mv.
g Connect Voltmeter to 50 ΩOUTPUT.
h. Set Video Amplifier SENSITIVITY to 100 mv.
i. Connect Oscillator to INPUT and set to 100 kc.
j. Adjust Oscillator output for 300 mv indication on Voltmeter.
k. Observe that Counter correctly counts input frequency.
3. MAXIMUM INPUT: 5 volts rms, 100 vdc
a. Set counter controls as in 1 a.
b. Connect BNC tee to Video Amplifier INPUT, set Model 711A DC Power Supply for 100volts, add 1 megohm
series resistor, and connect power supply to Video Amplifier.
c Use a 0.1 µf, 200 wvdc capacitor and connect Oscillator and Voltmeter to INPUT. Set Oscillator for 100 kc
and 5 volts rms as indicated on Voltmeter.
d.. Observe that counter correctly displays input frequency. (cont’d)
5-2

Model 5261A
Section V
Paragraphs 5-14 to 5-18
TABLE 5-2. In-Cabinet Performance Checks (cont’d)
4. MONITOR: OUTPUT METER indicates acceptable signal level to Counter
a. Set Counter controls as in 1 a and Video Amplifier SENSITIVITY to 3 ’MV.
b. Set Oscillator to 100 kc and connect to Video Amplifier INPUT with 50-ohm termination.
c. Connect Voltmeter to 50 19 OUTPUT with 50-ohm feedthrough termination.
d Adjust Oscillator output level for 420 mv on Voltmeter
e. Observe that OUTPUT LEVEL meter indicates at right edge of green portion of scale and Counter correctly
displays input frequency.
g Observe that OUTPUT LEVEL meter indicates at left edge of green portion of scale and Counter correctly
displays input frequency.
5. ACCURACY: retains accuracy of Model 5243L or Model 5245L Electronic Counter.
a. Set Counter controls as in 1 a.
b. Set Oscillator frequency to 100 kc and connect to Video Amplifier INPUT.
c. Set Video Amplifier SENSITIVITY to 100 MV.
d. Connect Voltmeter to Oscillator output and set signal level to 100 mv.
e. Observe and record Counter display.
f. Set Counter SENSITIVITY to .1V. Disconnect Oscillator output from Video Amplifier INPUT and connect to
Counter AC SIGNAL INPUT.
g. Observe that Counter display corresponds with value recorded in step e.
6. AUXILIARY OUTPUT’
a. 50 ΩOUTPUT on front panel lor monitoring amplified signal to Counter or for driving external equipment
checked in 1 under BANDWIDTH specification check.
b. 1 mv signal at Video Amplifier INPUT provides at least 100 mv at 50 ΩOUTPUT, checked in 2 under INPUT
SENSITIVITY specification check.
c. Maximum undistorted output is 300 my into 50-ohhm load, checked in 2 under INPUT SENSITIVITY
specification check.
d. Set Video Amplifier SENSITIVITY to 100
MV. Adjust Oscillator output for 420 mv on Voltmeter.
e. OUTPUT LEVEL meter should indicate at
right edge of green scale. If not, adjust A4R13 for this
indication.
f. Adjust Oscillator output for OUTPUT LEVEL
indication at left edge of green scale. Voltmeter should
indicate not less than 100 mv.
5-14. TROUBLESHOOTING AND REPAIR.
5-15. TROUBLESHOOTING.
5-16. When operation or performance checks indicate
an instrument malfunction, refer to Table 5-3
(Troubleshooting) for the more common indications of
trouble and checks to isolate the trouble. After the
trouble has been isolated to a particular assembly or
stage, voltage and resistance checks can be made to
determine the defective component.
5-17. PRINTED CIRCUIT COMPONENT
REPLACEMENT.
5-18. Component lead holes in the Mode I 5261A
printed circuit boards have plated walls to ensure good
electrical contact between conductors on opposite sides
of the board. To prevent damage to this plating and to
the replacement component, apply heat sparingly and
work carefully. The following replacement procedure is
recommended:
a. Remove defective component by applying
heat carefully to the component connection and lifting the
component from the board.
b. Melt solder in component lead holes. Use
clean dry soldering iron to remove excess solder. Clean
holes with toothpick or wooden splinter. Do not use
metal tool for cleaning. This may damage through-hole
plating.
c. Bend lead of replacement component to the
correct shape and insert component leads into
component lead holes. Using heat and solder sparingly,
solder
5-3

Model 5261A
Section V
Table 5-3
leads in place. Heat may be applied to either side of
board. A heat sink (longnose pliers, commercial heat-
sink tweezers, etc.) should be used when replacing
transistors and diodes to prevent conducting excessive
heat from the soldering iron to the component.
d. Through-hole plating breaks are indicated by
the separation from the board of the round conductor
pads against board and solder replacement component
lead to conductor pads on both sides of the board.
TABLE 5-3. Troubleshooting
Trouble Symptom Possible Cause
No output to Counter or 50 ΩOUTPUT DC voltages from Counter, FET A1Q1 dead,
jack A4Q4 shorted, P6(1) or J2 shorted
Low Video Amplifier gain AQ1 weak, A3Q1-A3Q6 weak, A4R5 increased
value
Output low at frequencies near 10 cps A4C6 open, A1C1, A3R18 increased value
Output Iow at frequencies above 100 kc A2C1 changed value, high frequency trimmers
A3C4 and A3C11 not correctly adjusted
Output noisy A1Q1 noisy poor ground connection at P6(3),
A3C5 ,or A3C12 changed value
5-4

Model 5261A
Section V
Figure 5-1
FIGURE 5-1. Schematic Diagram Notes.
5-5

Model 5261A
Section V
Figure 5-2
FIGURE 5-2. Top View, Component Location
5-6