Hp 654a Service manual

Fli;'

HEWLETT

.:e.

PACKARD

OPERATING

AND

SERVICE

MANUAL

MODEL

654A

TEST

OSCILLATOR

The

main

bod

y

of

this

manual

appli

es

to

Seria l Pre fix

0951

A

Any

changes

made

in

instruments

manufactured

after

this

printing

w i

ll

be

found

in

a

"Manual

Chan

g

es

"

supplem

e

nt

supplied

with

this

manual

. Be

su

re

to

ex

amine

this

s

upplement,

if

one

ex

ist

s

for

thi

s

manual,

fo

r

any

changes

which

apply

to

your

instrum

e

nt

and

record

these changes

in

the

manual.

Backdating

information

for

in

st

rum

e

n~s

ma

n

ufactured

before

thi

s

printing

will

be

found

in

Appendix

C

for

in s

trume

nt Serial

Numbers

0951

A02260

and b e

low

.

WARNING

I

To

help

minimize

the

possibility

of

electrical

fire

or

shock

hazards,

do

not

expose

this

instrument

to

rain

or

excess

moisture.

·hp- Part No. 00654-90003

Microfiche Part No. 00654-90053

Company

1969

P .O. Box

30),

Loveland ,

Colorado

80537

U.S.A.

Printed: October 1975

FliO'l

HEWLETT

~-------------------~~

PACKARO

CERTIFICA

TlON

Hewlett-Packard Company certifies that this product met its published specifications at the time

of

shipment

from

the

factory. Hewlett-Packard further certifies that its calibration measurements

are

traceable to the United States

Na-

tional Bureau

of

Standards, to the extent allowed by the Bureau's calibration facility, and to the calibration facilities

of

other International Standards Organization members.

WARRANTY

This Hewlett-Packard

product

is

warranted

against defects in material

and

workmanship

for a period

of

one

year

from

date

of

shipment [,except that in the case

of

certain

components

listed in Section I

of

this

manual,

the

warranty

shall be for the specified period) .

During

the

warranty

period,

Hewlett-Packard

Company

will, at its

option,

either

repair

or

replace

products

which prove to be defective.

For

warranty

service

or

repair, this

product

must be

returned

to

a service facility designated by -hp-. Buyer shall

prepay

shipping charges

to

-hp-

and

-hp- shall pay shipping charges

to

return

the

product

to

Buyer. However, Buyer

shall pay all shipping charges, duties,

and

taxes for

products

returned

to

-hp-

from

another

country.

Hewlett-Packard

warrants

that

its

software

and

firmware designated by -hp-

for

use with

an

instrument

will execute its

programming

instructions when properly installed

on

that

instrument.

Hewlett-Packard

does

not

warrant

that

the

operation

of

the

instrument,

or

software,

or

firmware will be

uninterrupted

or

error

free.

LIMITATION

OF

WARRANTY

The

foregoing

warranty

shaH not

apply

to

defects resulting

from

improper

or

inadequate

maintenance

by Buyer,

Buyer-supplied

software

or

interfacing,

unauthorized

modification

or

misuse,

operation

outside

of

the

environmental

specifications for

the

product,

or

improper

site

preparation

or

maintenance.

NO

OTHER

WARRANTY

IS

EXPRESSED

OR

IMPLIED.

HEWLETT-PACKARD

SPECIFICALLY

DISCLAIMS

THE

IMPLIED

WARRANTIES

OF

MERCHANTABILITY

AND

FITNESS

FOR

A

PARTICULAR

PURPOSE.

EXCLUSIVE

REMEDIES

THE

REMEDIES

PROVIDED

HEREIN

ARE

BUYER'S

SOLE

AND

EXCLUSIVE

REMEDIES.

HEWLETT-

PACKARD

SHALL

NOT

BE

LIABLE

FOR

ANY

DIRECT,

INDIRECT,

SPECIAL,

INCIDENTAL,

OR

CONSE-

QUENTIAL

DAMAGES,

WHETHER

BASED

ON

CONTRACT,

TORT,

OR

ANY

OTHER

LEGAL

THEORY

.

ASSISTANCE

Product

maintenance

agreements

and

other

customer

assistance

agreements

are available

for

Hewlett-Packard products.

For

any

assistance,

contact

your

nearest

Hewlett-Packard

Sales

and

Service

Office.

Addresses

are

provided

at

the back

of

this manual.

10/1/79

Model 654A

Table

of

Contents

TABLE

OF

CONTENTS

Section

Page

Section

Page

I. GENERAL INFORMATION

....

. . .

...

..

.

1-1

5-36. Hum and Noise Check

..

...

..

... ...

5-10

1-1.

Description......

...

....

.

.....

.

1-1

5-37 . Counter Output Check

..

. .

..

.

.....

5-11

1-7

. Supplied Accessories . . . . . . . . . . . .

..

1-1

5-38. Adjustment Procedure

...

..

.

.....

. . 5-12

1-8

. Recommended Accessories. . . . . . . . . . I-I

540.

Calibration Procedure

...

.. ..

. .

....

. 5 -12

1-9.

Instrument and Manual Identification

...

I-I

542.

Turn-On

..

.

.............

.

...

.5-13

545.

Power Supply Voltage Adjustments

...

5-13

Section

Page

546

. Power Supply Regulation and

11.

INSTALLATION 5-13

Zero Adju stment.

........

..

.. ..

3-1

5-88 . Trouble Isolation

in

the Remainder

Section

Page

5-95. Troubleshooting the Meter

.....

..

....

..

.....

. . .

2-1

Ripple Check

..

.

...

.

..

....

. .

2-1. Introduction 5-13

...

.

......

.

.........

2-1

547

. Frequency Calibration Procedures

..

2-3.

Initial Inspection

..............

.

..

2-1

5-58 . Meter Tracking and Amplitude

2-5. Power Requirements

...

.

..........

2-1

Control Adjustments .

...

.. ..

...

.5-16

2-9

. Ground i

ng

Requirements . .

....

. . .

..

2-1

5-61. Amplitude Accuracy Calibration .

..

5-17

2-11. Installation 5-18

...

... ...

...

....

..

.

..

2-1

5-62. Balance Adjustments

.......

.

.....

2-13. Rack/Bench Installation .

....

...

.. ..

2-1

5-65

.

Level

Flatness Adjustments .

...

.....

5-18

1-15. Repackaging for

Shipment.

. . . . . .

..

2-1

5-70. Troubleshooting the 654A

..

......

..

5-19

5-74. Front Panel Checks .

......

.

......

5-19

Section

Pa

ge 5-75. Troubleshooting Tree

..

.

.......

. . 5-19

Ill. OPERATING INSTRUCTIONS. . . . . . . . . .

3-1

5-78 . Troubleshooting the Power Supply

....

5-22

3-1. Introduction

5

-22

....................

3-1

5-81. Troubleshooting the Oscillator Circuit

.

3-3

. Control

s,

Indicators,

and

Connectors 5-23

....

3-1

5-84. Troubleshooting the Buffer Amplifier

..

3-5. Turn-On Proced ure . . . . . . . . . . . . . . .

3-

I 5-86. Troubleshooting the Balanced

3-6. Output Meter Mechanical Amplifier.

..

....... .......

...

5-23

3-8. Primary Power Application

..

...

.

...

3-1

of

the Leveling Loop

...

.

..

.

..

...

5-23

3-9. Operating Instructions

....

.

.....

...

3-1

5-91. Troubleshooting the Amplitude

3·

10.

Operating Check

.. ..

......

.

......

3-1

Control Integrator

..

...

......

...

5-24

5-93. Troubleshooting the A

LC

Loop

..

...

. 5

-24

IV.

THEORY OF OPERATION 5-24

......

.

.......

4-1

Differential Amplifier

..

.

.....

..

.

4-1. General Description

............

..

.

4-1

5-97. Troubleshooting the Attenuators

.....

5-24

4-6

. Circuit Description . . . .

...

. .

..

. . . .

4-1

5-99. Servicing Etched Circuit Boards

..

. .

..

5-24

4-7. Oscillator

Circuit.

. . . . . . . . . .

4-1

5-101. Servicing Rotary Switches .

.....

..

.5-25

4-11

. Buffer Amplifier

...

..

...........

4-2 5-103 . Servicing Tuner

Ass

embly . .

..

.

.....

5

-25

4-13. Counter Emitter Follower

..

.

......

4-2

4·15 . Balanced Amplifier

..............

4-2 Section

Pa

ge

4-19 . Amplitude Control and Automatic

VI

REPLACEABLE PARTS

....

... ...

..

....

6-1

Leveling Con trol

........

.

..

....

4-3 6-1. Introduction

..

....

...

.

...

.

...

6-1

4-29. Meter Circuits . . . . . . . . .

44

64.

Ordering Information

...

.

...

.

....

..

6-1

4-33. Attenuators

..

. . . . .

..

.

..

.

.. ..

4-4 6-6. Non-Listed Parts

....

..

...

.

.......

6- 1

4-35. Impedance

Se

lec tor. . . . . . . . .

44

4-37. Regulated Power Supply . . . . . . . .

4-4

Section Page

VII

CIRCUIT DIAGRAMS

..

.

......

...

......

7-1

7-1. Introduction

.....

.

..

.

...........

7-1

Section Page

V.

MAINTENANCE

..

...

......

.....

.

.....

5-1

5-1. Introduction .

...

.

...

..

......

.. ..

5-1

54

. Performance Checks. . . . . . . . . . . . .

5-1

5-6. Frequen

cy

Checks

..

...

..

. .

.....

.

5-1

5-7

. Frequency Range Check

...

....

.

....

5-1

5-8. Frequency Accuracy Check .

...

..

.

5-1

5-9. Amplitude Accuracy Checks. .

5-1

5-15.

Level

Flatness Checks

..

.

.........

54

APPENDICES

5-21. Meter Tracking Accuracy Check

.....

5-6

5-22. Attenuator Accuracy Checks

........

5-7

A.

CODE LIST OF MANUFACTURERS

5-28. Balance Checks. . . .

...

. .

..

5-

8

B.

SALES

AND

SERVICE OFFICES

5-35. Distortion Clleck . . . . . . . . . .

5-9

C.

BACKDATING

tii

Table

of

Contents Model 654A

LIST

OF

TABLES

Number

Page

Number

Page

]-1. Specifications

......

..

...........

.

1-2

5-2. Frequency Accuracy Check. .

............

5-3

1-2

. General Information

........

.

1-2

5-3. Thermal Converters for

Level

Flatness Checks

...

5-5

3-1. dBm/Voltage Conversion Chart

.....

.

3·1

54.

Frequency

Adjustments.

. . . . .

..

.

.......

5-13

5-1. Required Test Equipment

..

.

....

. 5·2 5-5. Front Panel Troubleshooting . . . _

..........

5-21

6-1. Replaceable Parts

...........

.

...

6-2

thru 6-12

LIST

OF

ILLUSTRATIONS

Number

Page

Number

Page

I-I.

Model

654A Test Oscillator.

1-2

5-11. Hum and Noise Check

..

5-1

I

2-1.

3-1.

Power Cords . .

Location

of

Con trois, Indicators

and Connectors

2-1

3-2

5-12 Logarithmic Additon

of

Harmonic Components

..

5-1

I

4-1.

RC

Network Characteristics

.....

.

4-1

5-13.

10MHz

Low

Pass

Filter . . .

..

5-11

4-2. Regulated Power Supply Output

5-\4.

Lo

ca

tion

of

Internal Adjustments. .

..

5-12

Voltage

vs

Current

4-5

5·15.

Fr

equency Calibration T

es

t

Setup..

.5-14

4·)

. Simplified Scllematic

of

Current 5-16. Meter Tracklllg Adjustment. . . . .5·17

Limiting Circuitry.

4-5

5-17. Alignment Access Covers for

5-1. Amplitude Accuracy Checks -UNBAL

5-3

Mod

e

ls

65 I

B,

2A, 3A, 4A. .

..

5-25

5·2. Amplitude Accuracy Checks -BAL.

54

5-

j

8.

Troubleshoot ing Tree. . . . 5-27/5-28

5-3.

Level

Fla1ness Checks.

54

6-1. Frequency Tuning

Me

chanis

m.

6-9

54.

Ref

ere

nce

Supply.

. . .

.. ..

. 5·5 6-2. Chassis Mechanical Parts. .

..

.

.....

. .

...

6-10

5-5. Meter Tracking Accuracy Check

..

5·6 7 -I. Block Diagram . .

7-3

5-6

. Attenua'tor Accuracy Checks

...

5·7 7-2. Oscillator and Buffer Ampl if

ier

....

.

7-5

5-7

. Impedance Converter

..

5·8 7-3.

Balan

ce

d Amplifier,

Met

er and

5-8. Balance Checks.

5-9

Levelin g .

..

7-7/7-8

5-9. Balance

Box

..

5·9

74.

Attenuato

rs

and Impedan

ce

Selector

...

.

..

7-9/7-10

5·]0. Distortion Check

........

. . . .5-10 7-5. Power Supplies,

AI

.....

7-11

iv

~

- 7

t-

--.'

~

" t _

l-

+----A..-

_ I •

.-

,

I~.'.

- . -

,I

"-'-~~.J.:o.l\..

_ 1.L.._

A

~

e

;·3

;·5

13

21

12

.

ge

II

·

11

·1

2

·1

4

·17

·25

·28

6·

9

·1

0

7·3

7·5

7·8

·10

·11

Fli;-

HEWLETT

&!e.I

PACKARD

SAFETY

SUMMARY

Thl

following

glnlrlillfity prlclutionl

mUlt

bl

obHrvld

during

III

phllel

of

operltion,

IlrvicI,

Ind

rlplir

of

thil

inltrumlnt.

Flilure

to

comply

with

thell

preclutionl

or

with

Ipecific

wlrningl

ellewhere

in

thil

mlnull viollt

..

Ilflty Itlndlrdl

of

delign,

mlnuflcturl,

Ind

intended

ule

of

the

inltrument.

Hewlett'Plcklrd

Complny

Illumel

no

Iilbility

for

the

cUltomlr'1

flilure

to

comply

with

theSl

requirementl.

Thil

il I Sifety

CII

..

1

inltrument.

GROUND

THE

INSTRUMENT

To minimize shock hazard,

the

instrument

chassis and

cabinet

must

be

connected

to

an elec-

trical

ground.

The

instrument

is equipped

with

a

three-conductor

ac

power

cable. The

power

cable

must

either

be plugged

into

an

approved

three-contact

electrical

outlet

or

used

with

a

three-contact

to

two-contact

adapter

with

the

grounding

wire

(green)

firmly

connected

to

an

electrical

ground

(safety

ground)

at

the

power

outlet.

The

power

jack

and

mating

plug

of

the

power

cable

meet

International

Electrotechnical

Commission

(IEC)

safety

standards.

DO

NOT

OPERATE

IN

AN

EXPLOSIVE

ATMOSPHERE

Do

not

operate the

instrument

in

the

presence

of

flammable

gases

or

fumes.

Operation

of

any

electrical

instrument

in such an

environment

constitutes

a

definite

safety

hazard.

KEEP

AWAY

FROM

LIVE

CIRCUITS

Operating personnel

must

not

remove

instrument

covers.

Component

replacement

and internal

adjustments

must

be made

by

qualified

maintenance

personnel. Do

not

replace

components

with

power

cable

connected.

Under certain

conditions,

dangerous

voltages

may

exist

even

with

the

power

cable removed.

To

avoid injuries,

always

disconnect

power

and

discharge

circuits

before

touching

them.

DO

NOT

SERVICE

OR

ADJUST

ALONE

Do

not

attempt

internal service

or

adjustment

unless

another

person, capable

of

rendering

first

aid and resuscitation, is present.

DO

NOT

SUBSTITUTE

PARTS

OR

MODIFY

INSTRUMENT

Because

of

the danger

of

introducing

additional

hazards,

do

not

install

substitute

parts

or

per-

form

any

unauthorized

modification

to

the

instrument.

Return

the

instrument

to

a

Hewlett

-

Packard Sales and Service

Office

for

service and repair

to

ensure

that

safety

features are main-

tained.

DANGEROUS

PROCEDURE

WARNINGS

Warnings, such as

the

example

below,

precede

potentially

dangerous

procedures

throughout

this manual.

Instructions

contained

in

the

warnings

must

be

followed.

I

WARNING

I

Dingeroul

voltagll, clplble

of

cluling

delth,

Irl

prelent

in

thil

inltrument.

Ule

ex·

treml

clution

whl"

hlndling,

tilting,

Ind

Idjulting.

A

SAFETY

SYMBOLS

General

Definitions

of

Safety

Symbols

Used

On

Equipment

or

In

Manuals.

Instruction manual symbol: the product will be marked with this

symbol when

it

is necessary for the user to refer to the instruction

manual

in

order to protect against damage to the

in

strument.

Indicates dangerous voltage (terminals

fed

from the interior

by

voltage exceeding 1000 volt s must

be

so marked).

Protective conductor terminal. For protection against electrical

OR

~

shock

in

case

of

a fault. Used with field wiring terminals to in-

'0

dicate the terminal which must

be

connected to ground before

operating equipment.

Low-noise or noisele

ss

, clean ground (earth) terminal. Used for a

signal common, as well as providing protection again st electrical

shock

in

case

of

a fault. A terminal marked with this symbol must

be connected to ground

in

the manner described

in

the

in

stallation

(operating) manual , and before operating the equipment.

Frame or chass

is

terminal. A connection to the frame (chassis)

of

rh

OR

..L

the equipment which normally includes all expos

ed

metal struc-

tures.

Alternating current (power line).

Direct current (power line) .

Alternating or direct current (power line).

I The

WARNING

sign denotes a hazard.

It

calls attention to a pro-

WARNING

cedure, practice, condition

or

the like, which, if not correctly per-

"'------

••

formed

or

adhered to, could result

in

injury

or

death to personnel.

The

CAUTION

sign denotes a hazard .

It

calls attention to an

operating procedure, practice, condition or the like , which,if not

correctly performed or adhered to, could result

in

damage to or

destruction

of

part or all

of

the product.

The NOTE sign

denote

s important information .

It

calls attention

NOT

E : to procedure, practice, condition

or

the like, which

is

essential to

highlight.

.-

~

-

.1-

_

.

-~.:..

Model

654A

Section I

SECTION

GENERAL

INFORMATION

1-1_

DESCRIPTlON_

1-2

. The Hewlett-Packard Model

654A

Test Oscillator

is

an

ideal

general purpose signal source whenever a flat balanced

or

unbalanced test signal

is

required . Balanced outputs

of

135

ohms, 150 ohms and 600 ohms have many uses

in

the

communications industry. Automatic leveling, together

with the expanded meter, make the

654A

ideally suited to

voltmeter calibration or to test frequency response

of

components during manufacture. The instrument

is

shown

in

Figure I-I and the specifications are listed

in

Table I-I.

General information relating to the instrument

is

listed

in

Table

1-2.

The information

in

Table

1-2

should not be

considered specifications.

1-3. The Model

654A

is

a stable,

low

distortion sine-wave

signal

source with a flat frequency response

of

+/-0.5% over

the frequency range

of

10Hz

to 10

MHz.

The attenuators

allow the signal to be adjusted

in

I

dB

and

10

dB

steps

from +10

dBm

to

-89

dBm, and the front panel

AMPLITUDE control allows a continuous adjustment

in

level

of

+/-1

dB

from the settings shown on the OUfPUT

LEVEL attenuators. The flat frequency response

is

achieved by automatic leveling circuits within the

654A.

1-4.

Five

output impedances are available, selected by a

front panel push-button control: these are 50 and 75 ohms

unbalanced and 135, 150 and 600 ohms balanced. Balance

is

greater than 50

dB

up to I

MHz

and greater than

40

dB

up to 5

MHz

.

1-5.

The meter scale

is

expanded to indicate 0 dBm at

center scale, with a total range

of

+/-1

dBm. The metering

circuit monitors the signal

level

before the attenuators

so

that the meter indication

is

independent

of

the attenuator

settings; the meter indicates the signal level set by the front

panel AMPLITUDE control. The

output

signal

level

into

the load

is

the algebraic sum

of

the meter indication and

the OUTPUT LEVEL attenuator settings.

1-6.

An

additional feature

is

the COUNTER OUTPUT rear

panel

BNC

connector. This allows the Model

654A

frequency to be continuously monitored by

an

electronic

counter without interrupting measurements or affecting

terminal balance .

1-7.

SUPPLIED

ACCESSORIES.

Rack mount kit: -hp- Part

No.

5060-0775.

1-8.

RECOMMENDED

ACCESSORIES.

-hp-

II

048C 50 ohm Feedthrough Termination

-hp-

II

094A

75 ohm Feedthrough Termination

-hp- 11095A

600

ohm Feedthrough Tennination

-hp-11l43A

Balanced

BNC

to Alligator clip cable

1-9.

INSTRUMENT

AND

MANUAL

IDENTIFICATION.

1-10.

Hewlett-Packard uses a two-section serial number.

The first section (prefix) identifies a series

of

instruments.

The last section (suffix) identifies a particular instrument

within the series. If a letter

is

included with the serial

number, it identifies the country

in

which the instrument

was

manufactured.

If

the serial prefix

of

your instrument

differs from the one

on

the title page

of

this manual, a

change sheet

will

be supplied to make this manual

compatible with newer instruments or the backdating

information

in

Appendix C

will

adapt this manual to earlier

instruments.

All

correspondence with Hewlett-Packard

should include the complete serial number.

1-1

Section 1 Model

654A

I

-

B l

floO

S }

r

Figure 1-1. Model

654

A Test Oscillator

Table

I-I.

Specifications

frequency

range: 10

Hz

to

10 MHz in 6 bands.

Frequency

accuracy:

100

Hz

(on

Xl

00

RANGE)

to

5 MHz: +/-2%

10

Hz

to 100 Hz: +/-3 %

5

MHz

to

10

MHz: +/-4%

Level flatness(+IO dBm and 0

dBm):

+/-0.5% referenced

to level

at

I kHz from

10Hz

to 10 MHz for un-

balanced

outputs,

10

Hz

to

5

MHz

for 135

ohm

and

150

ohm

outputs,

and 10

Hz

to I

MHz

for

600

ohm

output.

Attenuator

Range: 99 dB in 10 dB and I dB steps.

Accuracy: +/-1.5%

(0

.

15

dB)

except +/-10%

(I

dB)

at

output

levels below

60

dBm

at

frequencies greater

than

300

kHz.

Amplitude

control:

greater

than

2 dB.

Amplitude

accuracy:

+/-1

% for

90

days (at I kHz,

+ I 0 dBm level with

meter

centered).

Meter tracking: +/-0.05 dB.

Balance

(on

balanced impedances) when measured by the

procedure

given in Paragraph 5-28 : greater

than

50 dB

for frequencies from

10Hz

to I MHz, greater than

40

dB

to

5 MHz .

Distortion

(THD)

10Hz

to

I MHz : greater

than

40

dB below

fu

nda-

mental.

I

MHz

to

10

MHz: greater

than

34

dB below funda-

mental.

Hum

and

noise: greater than

70

dB

down

at

full

output.

Table 1-2. General

Information

Output

impedance:

50

ohm

unbalanced, 75

ohm

un-

balanced, 135

ohm

balanced, 150

ohm

balanced and

600

ohm

balanced.

Output

level:

+11

dBm to -90 dBm, 10 dB and I dB

steps

with adjustable

+/-1

dB

meter

range; calibrated for

each

impedance

.

Meter resolution:

0.02

dB.

1·2

Output

connectors:

BNC . Maximum voltage which can

be

applied

to

the

output:

less

than

+/-3 V peak.

Counter

output:

greater

than

0 .1 V rms

into

50

ohm

,

BNC

connector.

Operating

temperature:

OOC

to

+550 C

(32°F

to

130°F).

Power: 115 V

or

230

V +/ . 10%, 48

Hz

to

66

Hz,

30

W .

1/

1

nominal, 35 W max.

~

I

554A

Model

654A Section

II

SECTION

II

INSTALLATION

2-1.

INTRODUCTION.

2-2.

This section contains information and instructions

necessary for installing and shipping the Model 654A Test

Oscillator. Included are initial inspection procedures, power

and grounding requirements, environmental information,

installation instructions and instructions for repackaging for

shipment.

2·3.

INITIAL

INSPECTION.

2-4.

This instrument

was

carefully inspected both

mechanically and electrically before shipment. It should be

physically free

of

mars or scratches and

in

perfect electrical

order upon receipt. To confirm this, the instrument should

be

inspected for physical damage

in

transi t. Also. check for

supplied accessories, and test the electrical performance

of

the instrument using the proced

ure

outlined

in

Section

Vof

this manual. If there

is

damage or deficiency, see the

warranty on

Page

ii

of

this manual.

2·5.

POWER

REQUIREMENTS.

kHz, 2·6. This instrument

will

operate from either 115 or

230 V ac,

48

Hz

to 66

Hz.

The instrument can easily be

the position

of

the slide switch located

on

the rear panel, so

that the designation appearing on the switch matches the

nominal voltage

of

the power source.

the

o

dB

than

Be/ore applying primary power to the 654A

be slire it is set for the proper

fine

voltage

as

olltlined

in

Paragraph

3-8.

Inda-

2-7.

Power

Cords.

Inda-

2-8.

Figure

2-J

illustrates the standard power plug config-

urations that are

used

throughout the United States and

in

tput. other countries. The

-hp-

part number directly below each

drawing

is

the part number for a 654A power cord

equipped with a power plug

of

1hat configuration. If the

appropriate power cord

is

not included with the instru-

ment , notify the nearest -hp- Sales and Service Office and a

replacement cord will be provided.

2-9.

GROUNDING

REQUIREMENTS.

2-10.

To protect operating personnel, the National Electri-

cal

Manufacturer's Association (NEMA) recommends that

the instrument panel and cabinet

be

grounded. The Model

654A

is

equipped with a three-conductor power cord

which , when plugged into an appropriate receptacle,

grounds the instrument. The offset pin

on

the power plug

is

the ground connection.

8120-1351

8120-1369

8120-1689

STO·8-419~

'UL

LISTED FOR

USE

IN THE UNITED STATES

OF

AMERICA

Figure 2-1.

Power

Cords.

2-11.

INSTALLATION.

2-12. This instrument

is

fully transistorized: therefore no

special cooling

is

required. However, the instrument should

not

be

operated where the ambient temperature

is

outside

the limits specifed

in

Table 1·2.

2-13.

RACK/BENCH

INSTALLATION.

2-14. This instrument

is

initially shipped

as

a bench-type

instrument (unless ordered specifically

as

a rack-type) with

plastic feet and tilt stand

in

place. Conversion

to

a rack-

mounted inst rument can

be

accomplished

by

using the

rack-mounting kit and instruction furnished with

YOUl

inst rumen t.

2-15_

REPACKAGING

FOR

SHIPMENT.

2-16. The following

is

a general guide for repackaging for

shipment. If you have any question, contact your local

-hp-

Sales and Service Office_(See Appendix

at

the back

of

this

manual for office location.)

NOTE

If

the instrument is

to

be shipped to Hewlett-

Packard

for

service or repair, attach a

tag

to

the instrument identifying the owner and

indicating the service

or

repair to be accom-

plished; include the model number and full

serial

number

of

the instrument. In any corre-

spondence, identify the instrument

by

model

number

and serial number.

a.

Place instrument

in

original container if avail-

able. If original container

is

not available, a suit-

able one can

be

purchased from your nearest -hp-

Sales and Service Office.

2-1

Section II Model 654A

If

original conlainer

is

nol used.

b.

Wrap

insirllineni

in

heavy paper or plaslic before

placing

in

In

inner conlainer.

c.

Use

plenly

of

packing malerial

aroLind

all

sides

of

insirLimenl and proieci panel

faces

wilh cardboard

sl

rips.

d.

e.

Place inslrumenl and inner container

in

a heavy

carlon or wooden box

a'nd

seal

will] slrong lape or

i1lel~1

bands. .H I

Mark

shipping conlainer wilh

"DELICATE

INSTRUMENT,"

"FRAGILE"

ele.

2-2

-

11Jj

I L -.

,1,1..

!."

()54A

Model

654A Section Il[

heavy

.a

pe

or

SECTION

III

CATE

OPERATING

INSTRUCTIONS

3-1.

INTRODUCTION.

e.

Adjust the OUTPUT LEVEL attenuators and the

AMPLITUDE control for the desired signal output

3-2

. This section contains instructions and information level. The algebraic sum

of

the meter indication

necessary

for

the operation

of

the 654A Test Oscillator. and the attenuator setting

gives

the power level,

in

[ncluded

in

this section are identification

of

controls, dBm, into a load equal to the impedance selected

indicators and connectors, turn-on procedure, meter by the [MPEDANCE pushbutton. [n Table 3-1, the

mechanical zero adjustment and operating instructions. o dBm and +

10

dBm levels are converted to

voltage

for

each impedance.

3-3.

CONTROlS,lNDICATORS,

AND

CONNECTORS.

3-4

.

All

operating controls, indicators and connectors of

the 654A are identified and described

in

Figure

3-1

.

SWITCH

THE

10

DBM

STEP

ATTENUATOR

DOWN

BEFORE

3-5.

TURN-ON

PROCEDURE.

CONNECT[NG

TO

SENS[T[VE

EQUIPMENT, SUCH

AS

THERMAL

3-6.

OUTPUT METER MECHANICAL

ZERO

CONVERTERS,

SO

AS

TO

PREVENT

ADJUSTMENT

. DAMAGE

FROM

OVERLOAD[NG.

3 -7. The

Model

654A output meter

is

properly Table 3-1. dBm/Voltage Conversion Chart

mechanically zero-set when the meter pointer rests over the

-I

dBm

mark. Zero-set the output meter to obtain

maximum accuracy and mechanical stability

in

the

following manner.

With

LIN

E switch turned off, insert

pOinted object (such

as

tip

of

bal

.1 point pen) into recess on

adjustment wheel, and rotate wheel until meter pointer

rests exactly over

-I

dBm

mark.

3-8.

PRIMARY

POWER

APPLICATION

.

a. Before applying primary power to instrument, set

I

15

or 230

volt

slide switch (S3) to position which

indica tes primary voltage to be used.

f.

Connect the load to the output connectors.

Use

o

dBm

= I m watt into rated load.

Impedance odBm +10 dBm

50

ohm

75 ohm

135

ohm

150 ohm

600 ohm

0.224 V rms

0 .274 V rms

0.367 V

rms

0.387Vrms

0.775 V rms

0.707 V

rms

0.866 V rms

1.162Vrms

1.225 V rms

2.449 V

rms

the UNBAL connector for 50 ohm and

75

ohm

b.

Connect primary power to connector J

I.

Switch loads and both connectors (BAL)

for

135

ohm,

LINE switch

(S

I) to

ON

position : pilot lamp 150 ohm and 600 ohm loads .

(DSI)

will

glow .

3-10.

OPERATING

CHECK.

3-9.

OPERATING

INSTRUCTIONS.

3-11. Before making measurements using the 654A,

a.

Zero

-

set

meter (Paragraph 3-7) and turn perform the following front panel checks to ensure that

instrument on (Paragraph 3-8). your instrument

is

operating correctly.

b.

Set

the FREQUENCY RANGE switch and

a.

Turn AMPLITUDE control until white arrow on

FREQUENCY dial (with VERN[ER) to the knob

is

pointing up; meter should indicate

desired frequency. (Dial reading multiplied by approximately 0 dBm.

range

setting

gives

the frequency

in

Hz_)

b.

Turn

AMPLITUDE

control

extreme

c.

Connect a frequency counter to the rear panel counterclockwise; meter should indicate

-I

dBm or

COUNTER OUTPUT, if desired . less .

d. Select the required output impedance by pressing

c.

Turn AMPLITUDE control extreme clockwise;

the appropriate [MPEDANCE pushbutton. meter should indicate +I

dBm

or greater.

3-\

Section

III

Model 654A

~

'

~4A

fES

T

OSCILlATOR'j;;ffi:;t:t-

-

@

o

rt==f)1

AMF'LI

ruOE

o

FREQUENCY

dial (Cl A/B/C): Varies test

frequency continuously within each frequency

range. Dial reading multiplied by range setting

gives

the out put frequency

in

Hz

of

the 654A.

FREQUENCY RANGE switch (52): Selects one

of

six

frequency multipliers from

Xl

0 to X

1M.

Output Meter

(M

I): Monitors amplitude

of

654A

output prior to OUTPUT LEVEL attenuators.

Algebraic sum

of

meter indication and OUTPUT

LEVEL attenuator setting

gives

output power into

rated load.

Mechanical Zero Adjust: Allows meter to

be

mechanically zeroed, when instrument

is

off.

CD

OUTPUT LEVEL (54): Attenuates 654A output

signal

in

nine steps

of

I dBm each .

o OUTPUT LEVEL (54): Attenuates 654A output

signal

in

nine steps

of

10

dBm each.

CD

UNBAL

out put (14):

BNC

connector provides

an

unbalanced output signal. at impedances

of

50

ohms and

75

ohms.

BAL output (J3 and 14):

BNC

connectors provide

a balanced output signal

at

impedances

of

135

ohms, 150 ohms and 600 ohms.

IMPEDANCE switch (A4S J): Selects required

output impedance

of

instrument; pushbuttons are

interlocked

so

that when one

is

pressed the others

spring out.

@ AMPLITUDE control (R3): Allows adjustment

of

+/-1

dBm

of

output signal amplitude.

®

FREQUENCY

VERNIER: Provides a fine

frequency adjustment for FREQUENCY dial.

@ LINE

ON

switch (51) and Pilot Lamp (DSI):

Switch applies primary power to instrument; pilot

lamp glows to indicate application

of

primary

power.

115

Vor

230 V Slide Switch (53): Sets instrument

® to operate from a primary power source

of

either

I

15

V

ac

or 230 V ac, 48

Hz

to 66

Hz.

FUSE

(FI):

0.4 amp slow blow fuse protects

® instrument from overloads.

COUNTER OUTPUT (12):

BNC

connector

® provides signal output

of

greater than

0.1

V

rms

into a 50 ohm load , at same frequency

as

front

panel out puts.

® Primary Power Connector

(1

I): Connects primary

power to instrument.

Figure 3·1. Location

of

Controls, Indicators and Connectors

3·2

:1654A

uired

IS

are

thers

nt

of

fine

lSI):

pilot

mary

nent

ither

tects

~ctor

rms

'ront

THEORY

OF

4-1.

GENERAL

DESCRIPTION.

4-2. The Model 654A Test Oscillator (see Block Diagram,

Figure 7-1) contains a

Wien

Bridge Frequency Adjustable

Oscillator

(10Hz

to

10

MHz)

followed by a Buffer

Amplifier and a Balanced Amplifier with a single ended

input and balanced output. The output

of

the Balanced

Amplifier

is

a leveled, sinusoidal signal; this signal passes

through Balanced Attenuators and a Balance and Unbalance

Impedance Switch (output impedance switching network)

to

the front panel output connectors.

4-3

. An

Average

Responding Detector monitors the

output

from

the Balanced Amplifier to provide two

dc

currents

(proportional to the

signal

level); one current flows to the

meter circuits and the other to the Amplitude Control

Integrator.

Au

tomatic leveling

of

the 654A

signal

is

achieved by means

of

the Amplitude Control Integrator

which compares the current from the

Average

Detector

with the current

from

an Amplitude Current Reference to

regulate the current through the lamp

of

a photosensitive

control device (A2DSVI). The lamp controls the imped-

ance

of

a resistive divider at the inpu t

of

the Buffer

Amplifier

so

as

to maintain a constant

output

level

from

the Balanced Amplifier. The

output

level

attenuators

provide attenuation

in

10

dB

and I

dB

steps

at

the output

connectors and a front panel AMPLITUDE control gives

2

dB

of

continuous output

level

adjustment by varying the

current from the Amplitude Current Reference.

4-4. The current from the Average Detector which flows

to

the meter circuits

is

divided into two parts : a fixed amount

of

current (approximately 1.25 rna)

flows

into the Meter

Offset Current Reference and the remainder

flows

to the

meter.

In

this way the meter

is

offset

so

that

it

indicates

only over the range

of

-I

dBm to +I dBm. The current

flowing into the Meter Offset Current Reference

is

held

con~tan't

by

the Meter Differential Amplifier which clamps

the Input of the current reference to a virtual ground.

4-5.

A Counter Emitter Follower provides isolation

between

th

e oscillator circuit and the rear panel COUNTER

OUTPUT.

Regulated Power Suppli

es

provide the +

31

V

and -

26

V reqUired to operate the 654A.

4-6.

CIRCUIT

DESCRIPTION_

4-7.

OSCILLATOR

CIRCUIT

(Schematic

No

.

1,

Figure

7-2)

4-

8.

The frequency adjustable Oscillator drives the Buffer

Model

654A Section

IV

SECTION

IV

OPERATION

Amplifier with a stable sine

wave

at a frequency determined

by the setting

of

the FREQUENCY RANGE switch and the

FREQUENCY dial. The circuit

is

a

Wien

Bridge Oscillator

which

has

a standard, frequency selective,

RC

leg

and a

resistance

leg

modified by the addition

of

a variable

impedance (A2CR I and A2CR2). A2Q26 and

A2Q

I

through A2Q6 comprises the amplifier section and

A2Q7

is

a peak detector which provides negative feedback to the

bridge

for

leveling. Two types

of

feedback are used; positive

feedback from the frequency selective network drives the

base

of

A2Q3 through the source follower A2QI, and

negative feedback from the resistive side

of

the bridge

drives the base

of

A2Q2. A2Q2 and A2Q3 form a

differential amplifier. Only

at

the selected frequency does

the positive feedback overcome the negative feedback to

sustain oscillations.

4-9. The six frequency ranges are selected by means

of

the

RC

networks mounted on the FREQUENCY RANGE

switch (S2); continuous adjustment

of

the frequency on

each range

is

accomplished by rotating the FREQUENCY

dial, which controls the setting

of

the tuner capacitors

CI

A,

CI

Band

CI

C.

The signal from the amplifier out put (from

A2Q5 and A2Q6)

is

developed across the

RC

network

of

the bridge; at the selected frequency, where Xc = R (Figure

4-1), the positive feedback to the base

of

A2Q3

has

the

correct phase and sufficient amplitude to sustain

oscillations. The high input impedance

of

the

field

effect

transistor

(A2QI)

prevents the amplifier from loading the

frequency determining

leg

of

the bridge; the feedback

prOVided

by A2Q26 prevents any changes

in

the parameters

of

A2QI from affecting the frequency response

of

the

amplifier. The difference between the positive and negative

FREQUENCY

0.5

/

'\

/

/ \ ////

/

////

\

/

/'

"

7/

/

//

",,/

~

LAG

0.4

0.3

_F_

p_

PHASE

F

0.1

LEAD

F

p;

POSITIVE

FEEDBACK

TO

AMPLIFIER

RATIO--

PHASE

-----

F ;

FEEDBACK

TO

RC

NETWORK

6!54A-A-187

9

Figure

4-1

.

RC

Network Characteristics

4-1

4-2

Section

IV

feedback signals

is

amplified by the differential amplifier

(A2Q2 and A2Q3) and applied, through emitter follower

A2Q4, to the complementary symmetry pair A2QS and

A2 Q

6.

The very

low

output impedance

of

the

complementary pair acts

as

a constant voltage source

for

the Buffer Amplifier and

also

allows feedback to

be

applied

to the bridge without loading the output

of

the oscillator.

A2QS

and A2Q6 are forward biased through A2CR7 and

A2CRS

so

as

to conduct slightly when

no

signal

is

applied;

this eliminates crossover distortion

of

the output signal.

4-10 . A2Q7 acts

as

a peak detector. Part

of

the oscillator

signal

is

superimposed on a negative bias at the base

of

A2Q7; A2Q7 conducts only when the positive peaks

of

the

signal overcome the negative bias. The negative dc output

of

A2Q7

is

filtered by A2C2, A2C3 and A2C4 and used to

bias

the diodes A2CRI and A2CR2

so

as

to vary the

impedance of the negative feedback side

of

the bridge to

control the amplitude

of

oscillations.

A2RS

is

switched into

the circuit on the

XI

00 through

XI

M ranges and

A2CS

on

the

XIO

through

XI

K ranges

for

extra filtering. A2CR3

limits any reverse voltage transients across the polarized

capacitors

A2C3

, A2C4 and A2CS. A2R9*

is

selected to

draw current from the bridge

so

as

to balance the current

through A2CR I and A2CR2 and improve distortion

in

the

output signal.

4·11.

BUFFER

AMPLIFIER.

(Schematic

1)

4·12 . The BtJffer Amplifier (A2QS through A2Q I0)

provides isolation between the oscillator and the Balanced

Amplifier and

is

also

used

as

the point at which the 6S4A

signal

is

leveled.

A2QS

and A2Q9 form a differential

amplifier whose output, from the

co

llector

of

A2Q9,

is

amplified by A2QlO and

fed

to the Balanced Amplifier.

Part

of

the signal output from

A2Q

lOis applied

as

negative

feedback through A2R39 to the base

of

A2QS

to stabilize

the amplifier gain over its

10Hz

to

10

MHz

frequency

range. The signal from the oscillator

is

divided down at the

input to the Buffer Amplifier by a resistive divider

consisting

of

A2R33 and the

resi

stive element

of

the

photosensitive resistor (A2DSV

I).

The resistance

of

the

resistive element

is

determined by the current through the

lamp, which

is

controlled by the Automatic Leveling

Circuits (Paragraph 4-19 and following) . The signal

level

at

the input of the Buffer Amplifier varies with changes

in

the

resistance of the photosensitive resistor to control the

level

of

the 6S4A output signal.

4·13.

COUNTER

EMITTER

FOLLOWER.

(Schematic

1)

4-14. The Counter Emitter Follower

(A3Ql)

serves

as

isolation between the Oscillator circuit, and the rear panel

COUNTER OUTPUT (12). The output frequency

is

the

same

as

the Variable Test Oscillator frequency .

Signal

amplitude at the COUNTER OUTPUT

is

approximately

0.1

V

rms

into a

50

ohm load .

4-15.

BALANCEO

AMPLIFIER.

(Schematic

2,

Figure

7-3)

Model6S4A

4-16. The single-ended sinusoidal output from the Buffer

Amplifier

is

amplified and converted into a balanced

signal

\\

in

the Balanced Amplifier. The Amplifier consists

of

three'll

cascaded differen tial amplifiers (A2Q II through

A2Q

16)

and two complementary symmetry pairs (A2Q IS, A2QI9

and A2Q20, A2Q21). The balanced

output

signal from the

complementary symmetry pairs

is

developed across

summing resistors A2R74 and A2R7S and then applied

through A2R76 and C9, and through A2R77 and

CIO

to

the attenuators (S4). The input sinusoidal signal at the base

of

A2QII

is

converted into two signals

of

equal amplitude,

but

ISOo

out

of

phase, taken from the collectors of A2QII

and

A2Q

12. The two signals then follow parallel paths,

while maintaining the

ISO

o phase relationship, through the

Balanced Amplifier. One signal path

is

through

A2QII,

A2Q

13

and A2Q

15

to the complementary symmetry pair

A2QIS and A2Q19 ; the other signal path is through

A2Q12, A2QI4 and A2QI6 to complementary symmetry

pair A2Q20 and A2Q21. The complementary pairs are

biased through diodes A2CRIS, A2CRI6 and A2CRI7,

A2CRIS

so

that the transistors conduct slightly when

no

signal

is

applied; this eliminates crossover distortion

of

the

signal at the

output

of

the Balanced Amplifier.

4-17. The gain

of

the Balanced Amplifier

is

stabilized by

means

of

negative feedback. A2RSI couples the output

signal from the top

of

A2

R74 back to the base

of

A2Q

II

and A2RS3 couples the opposite signal from the bottom

end

of

A2R7S back to the base

of

A2Q12. Note that the

~

r

application

of

feedback together with the

high

gain

of

th

e

~

.

Amplifier and the very low signal source impedance (from '

the Buffer Amplifier) causes the Balanced Amplifier

to

function

as

an operational amplifier with differential input

and output;

as

a result , the overall gain

of

the Balanced

Amplifier

is

determined by the ratio

of

A2RSI to A2R44

and A2RS3 to A2RS4. Capacitors

A2C1S

and

A2C1S

improve the

high

frequency r

es

ponse

of

the feedback paths.

4-IS. To maintain proper balance

of

the output signal, the

junction

of

summing resistors A2R74 and

A2

R7S

is

held at

virtual ground by means

of

negative feedback to the third

differential amplifier (A2QIS, A2QI6). The differential

pair A2Q22 and A2Q23 compares the voltage at the

junction of A2R74 and A2R7S with ground (the base of

A2Q23

is

connected directly to ground). Any signal

unbalance or common mode signal across the two resistors

moves their junction away from ground; this voltage at the

junction

is

amplified by A2Q22 and A2Q23 and applied to

the base

of

A2Q

17

to change its coll

ec

tor current.

A2Q

17

is

the source

of

current

for

A2Q

15

and

A2Q

16

so

that the

change

in

current through them

will

be

such

as

to

re

store

the balance between the two sinusoidal signals and return

the junction

of

A2R74 and A2R7S back to ground. A2C32

is

adjusted for equal signal voltage across A2R74 and

A2R7S. A2R47, A2C16, A2C23, A2C26 , A2C27,

A2C2S

and A2C29

all

serve

as

frequency shaping elements

to

improve the frequency response and to insure stability of

the Balanced Amplifier over its frequency range

of

10Hz

to

10

MHz.

lei

654A

e Buffer

ed

signal

of

three I

A2Q16)

. A2QI9

~

rom

the

across

applied

I

CIO

to

the base

Iplitude,

, A2QIl

!I

paths,

)ugh the

A2QII,

!try pair

through

'mmetry

lairs

are

l2CR17,

...,hen

no

n

of

the

lized

by

output

. A2QII

bottom

that the

n

of

the

:e (from

lifier to

ial

input

lalanced

A2R44

A2C18

k paths.

~al,

the

;

held

at

he

third

ferential

at the

base

of

f

signal

resistors

~e

at

the

'plied

to

A2QI7

that the

restore

i return

A2C32

74 and

A2C28

lents to

lility

of

o

Hz

to

Model

654A

4-19.

AMPLITUDE

CONTROL

AND

AUTOIVlATIC

LEVELING

CONTROL.

4-20. The amplitude

of

the balanced sine

wave

Signal

from

the Balanced Amplifter

is

independent

of

the Attenuator

settings but can be varied over a 2

dB

range by the front

panel AMPLITUDE control (Schematic 2). The Automatic

Leveling Circuit (ALC) consists

of

the Average Detector,

the Amplitude Control Integrator, and the Amplitude

Current Reference (varied by the AMPLITUDE control).

The

Average

Detector monitors the output

of

the Balanced

Amplifier and produces a dc current proportional to the

amplitude

of

the Balanced Amplifier signal. The Amplitude

Control Integrator compares this dc current with a current

of

opposite polarity from the Amplitude Current

Reference; any difference

in

magnitude between the

current from the Average Detector and the reference

current

is

used

to apply negative feedback to the

photosensitive resistor at the input

of

the Buffer Amplifier

until the output

of

the Balanced Amplifier

is

at the level

where the two currents are equal. The output

of

the

Balanced Amplifier

is

at the required

level

when the current

from the Average Detector

is

equal to the reference current.

4-21. AVERAGE DETECTOR. (Schematic 2)

4-22. The detector monitors the output

of

the Balanced

Amplifier. A2Q24 and A2Q25 form a high

gain

amplifier

which

is

a current source for the detector (A2CR21 and

A2CR22).

A2CR21

supplies the metering circuits with a

positive dc current and A2CR22 supplies the

ALC

circuits

with a negative dc current. These currents are equal

in

ampl.itude to each other and proportional to the amplitude

of

the Balanced Amplifier output signal. A2Q24 and

A2Q25

(together with the components connected to the

base

of

A2Q25) form essentially one transistor with high

gain, high output impedance and very

low

output

capacitance; these factors together with the 'bootstrap'

capacitor A2C42 account for the amplifier's effectiveness

as

a current source over a wide frequency and temperature

range.

A2C43 (Freq. Response)

is

adjusted

for

flat

frequency response

of

the detector circuit.

4-23

. AMPLITUDE CURRENT REFERENCE.

(Schematic 2)

4-24. Zener Diode A I CR8 maintains a constant voltage

across

R3

(front-panel AMPLITUDE control) and A2R91

in

series, the Amplitude Control Integrator ma.intains

essentially 0 Vdc at the output

of

the current reference (at

the

base

of

A3Q6): thus, for any

given

setting

of

R3, there

IS

a

fixed

voltage drop across

A3Rl9

and

A3

R20 and a

fixed

amount

of

current flows from the Amplitude Current

Reference.

When

the setting

of

the AMPLITUDE control

~R3)

is

changed , the voltage drop across

A3

R

19

and A3R20

IS

changed ; this sets a new fixed value

of

current

flOWing

towards the base

of

A3Q6 .

4-25. AMPLITUDE CONTROL INTEGRA TOR.

(Schematic 2)

4-26. The

ci

rcuit consis

ts

of

A3Q6 through A3Q9 and

Section

IV

associated circuitry, including the lamp

of

the photo-

sensitive resistor A2DSV I (Schematic

I)

.

A3Q6

and A3Q7

form a differential amplifier; any change

in

output from the

collector

of

A3Q7

is

amplified by A3Q8 and applied to the

base

of

A3Q9 to change the current through the lamp

of

the photosensitive resistor (A2DSVI). Changes

in

lamp

current change the impedance

of

the voltage divider at the

input

of

the Buffer Amplifier (paragraph 4-12), thus

changing the sine wave signal

level

through the Buffer

Amplifier and the Balanced Amplifier. The

dc

current from

the Average Detector

is

compared,

at

the base

of

A3Q6,

with the current from the Amplitude Current Reference.

In

the differential pair (A3Q6, A3Q7) the base

of

A3Q7

is

connected directly to ground; therefore, as long

as

the base

of A3Q6

is

held at 0 Vdc, there will

be

no

change

in

output

from the collector

of

A3Q7. The amplitude

of

the positive

current flowing from the Amplitude Current Reference

is

ftxed; the amplitude

of

the negative current flowing from

the Average Detector depends

on

the level

of

signal at the

output

of

the Balanced Amplifier. These currents are

summed

at

the base

of

A3Q6 . The difference current flows

into the base

of

A3Q6. The amplitude

of

the base current

is

set

by

the AMPLITUDE CAL. adjustment and the

AMPLI-

TUDE control.

As

long as this current

level

is

not changed

by a variation

in

the Average Detector output, there will be

no

change

in

current through the lamp

of

the photo-

sensitive resistor; thus the

ac

signal level at the

ou

tput

of

the Balanced Amplifier will be constant.

In

this condition,

the

ALC

loop

is

in

the "quiescent" state and the output

of

the 654A

is

at the required level.

4-27. Suppose that the output

level

of

the Balanced

Amplifier

now

changes for some reason (e.

g.

the frequency

of

the

Wien

Bridge Oscillator

is

changed); then the

Amplitude Control Integrator

will

act to return the signal

back to

it

s original level

in

the

follOWing

manner:

a.

The negative current from the Average Detector

(A2CR22)

will

change proportionally with the

change

in

ac

signal level. This current flowing into

the summing node at the base

of

A3Q6

diminishes

the positive current amplitude thus decreasing the

base current to A3Q6. TIlls,

in

turn, begins to shut

off

the transistor.

b.

The output

of

the Amplitude Control Integrator

changes

in

response to the new input

so

as to

change the

ac

signal

level

into the Buffer Ampli-

fier.

TIlls

will

be

in

such a direction

as

to

return

the Balanced Amplifier

ac

ou

tput back to the

level

where the

nega

live

dc

current from the Average

Detector

is

again equal to its quiescent value.

In

this way the 654A

ou

tput signal

is

maintained at a

constant level.

4-28. To manually control the 654A output

level

over the

2

dBm

range, the AMPLITUDE control setting

is

changed;

this changes the current from the Amplitude Current

Reference thus changing the base current to A3Q6. The

Amplitude Control Integrator now acts

as

before to change

the Balanced Amplfier

ac

output

level

until the current

4-3

4-4

Section

IV

differential at the base

of

A3Q6

is

equal to its quiscent

value. The

ALC

circuit contains an integrator for fast

response without overshoot and without sacrificing the

ability to reject ripple superimposed

on

the curr.ent from

the Average Detector. S2C14

is

switched

in

parallel with

A3Cl0

on

the XIO RANGE for required response

of

the

Amplitude Control Integrator

at

low frequencies.

4·29

.

METER

CIRCUITS.

(Schematic

2)

4·30. The meter circuits consist

of

the Meter Differential

Amplifier, the Meter Offset Current Reference and the

Meter.

As

explained

in

Paragraph 4·22, the Average

Detector (A2CR2] and A2CR22) monitors the Balanced

Amplifier output and produces two

dc

currents, equal

in

amplitude but opposite in polarity, proportional to the

Balanced Amplifier

output.

The positive output

of

the

Average Detector (from

A2CR2l)

flows to the meter

circuits. A fixed part

of

this curren t flows into the Meter

Offset Current Reference and the remainder flows through

the Meter and

its

shunt resistors

A3Rl7

and A3RIS. The

Meter

(M])

is

calibrated to indicate center scale when the

654A output into rated load (the attenuators set

at

0 dBm)

is

0 dBm. The total range

of

the meter scale

is

+/·1

dBm so

that when the Meter indicates·] dBm, no current

is

flowing

through the Meter and

all

of

the current from the Average

Detector

is

flowing through the Meter Offset Current

Reference circuit.

4·3 I. The action

of

the Meter Offset Current Reference

and

the Meter Differential Amplifier

is

very similar to the

action

of

the Amplitude Current Reference and the

Amplitude Control Integrator (described

in

Paragraphs 4·22

through 4-25) . Apart from a

few

minor differences the

circuits are identical.

4-32. The Meter Offset Current Reference consists

of

A3R6, A3R7, A3RS, A3R9 and A3CR2. A3CR2

is

a

special temperature compensated Zener diode which

maintains a constant voltage across A3R7 and A3RS

in

series. Thus. the current flowing into the circuit

is

determined essentially by the voltage across A3R9 . This

current must always

be

a fixed amount

so

as

to offset the

Meter scale correctly ; therefore, the voltage across

A3

R9

must always

be

fixed; this

is

achieved by means

of

the

Meter Differential Amplifier. The Meter Differential

Amplifier consists

of

A3Q2 through A3Q5. A3Q2 and

A3Q3 form a differential pair; since the base

of

A3Q3

is

connected directly to ground, the base

of

A3Q2

will

be

held at a virtual ground. Any difference between the two

bases causes

an

output change from the collector

of

A3Q3

which

is

amplified by A3Q4 and applied to A3Q5 so

as

to

return the base

of

A3Q2 back to virtual ground. One side

of

A3R9

is

connected

to

the base

of

A3Q2, which

is

clamped

to a virtual ground; the other side

of

A3R9

is

connected to

a constant voltage point (set by A3R7); thus the voltage

across A3R9

is

held constant

as

required, and the Meter

Offset Current Reference always takes a fixed amount

of

the current from the Average Detector to offset the Meter.

A3C5 serves to improve the frequency stability

of

the

Model 654A

Meter Differential Amplifier. A3C6

is

connected across the

Meter to damp the meter movement, and A3C7

is

switched

in paraUel with A3C6 on the XIO RANGE so

as

to

further

improve damping

of

the Meter at very low frequencies.

1\

4·33.

ATTENUATO

RS.

(Schematic

3)

4·34. The balanced sine wave signal, developed across

A2R74 and A2R75

in

the Balanced Amplifier,

is

fed

through A2R76 and C9, and through A2R77 and

CIO

to

the Attenuators (S4). The attenuator assembly (S4) consists

of

four attenuators; a ]

dB

step and a

10

dB

step attenuator

connected

in

series

for

each

of

the two

halves

of

the

balanced signal. Each attenuator consists

of

four resistive

networks which are switched

in

various combinations to

give

the required attenuation. The front panel controls

consist

of

two concentric rotary knobs labelled OUTPUT

LEVEL dBm; the outer control, marked

in

10

dB steps,

controls

both

of

the

10

dB

step attenuators simultaneously;

the inner control, marked

in

]

dB

steps, controls both

of

the 1

dB

step attenuators simultaneously.

4·35

.

IMPEDANCE

SELECTOR.

(Schematic

3)

4-36. The front panel IMPEDANCE switch

(A4S])

selects

the reqUired

output

impedance

of

the 654A. The

impedance networks and the switching connect ions are

shown on schematic 3; the switch connections are shown

with the 50 ohm UNBAL

button

pushed.

In

the

BAL

mode, both front panel

output

connectors,

13

and 14,are

used;

in

the UNBAL mode, only 14

is

used. ,r

4·37.

REGULATED

POWER

SUPPLY.

4-38 . The regulated power supply provides

all

dc

voltaged

required

by

the 654A Test Oscillator circuits. The power

supply consists

of

a

+31

V

and·

26

V series regulated

supply. Each power supply is protected

by

current limiting

and foldback current limiting .

4·39 . Tile +3] V and -26 V power supplies are functially

identical. Both

use

operational amplifiers for output voltage

error amplification . AI R40 adjusts the

+3

I V supply

voltage

and

A I

R41

adjusts the .

26

V supply voltage .

4-40. Conventional current limiting

is

used

in

both supplies

to

limit the

output

curren I

to

approximately 300

mA

o

Foldback current limiting further limits the

output

current

if the

output

voltage

is

pulled below approximately

16

V

by a malfunction

in

the 654A circuitry. A direct short to

ground

of

either supply

will

result

in

an

output current

of

approximately

10

mA

as

shown

in

Figure 4-2.

441.

Figure 4·3

is

a simplified schematic

of

the current

limiting circuitry used

in

the 654A power supplies.

The

Current Limiting Transistor A I Q4(

+)

or AI Q7( - )

is

a

variable shunt to the series regulator drive current.

It

is

first

switched on

by

the voltage drop across tile Currellt

LimIt

Sensing Resistor when the power supply output current

reaches approximately 300

mAo

The power supply

will

remain

in

this Conventional Current Limit condition until

the output current decreases allowing the supply to return "

to normal operation,

Of

until the power supply output

~J

voltage drops below the Foldback Reference (]6.2V).

llo4ITEA

----

--,

I

SEAlES

REGULAT~

~

'I

OKJO(

SWrTCH

I

FOLDBACI(

L

__

~~tfE

SHUNT

CUAAENT

DAIVE CURRENT

L.

___

____

.....

__

el654A

Model

654A

:ross

the

witched

, further

.es.

~V~

_______

R~E~~~~~TE~D~~~T.~G~E

________

~

I across

,

is

fed

cia to

consists

:enuator

of

the

resistive

tions

to

controls

IUTPUT

B steps, IOOmA

200mA

300m

A

~

f-

3

10V

OUTPUT CURRENT

leously;

both

of

Figure

4-2.

Regulated

Power

Supply

Output

Voltage

vs

Current.

) selects

A.

The

ions are

~

shown

he

BAL

j J4, are

voltaged

e power

ogulated

limiting

JIlctially

. voltage

supply

voltage.

supplies

00

rnA.

curren t

Iy

16

V

short to

Hent

of

current

ies. The

- )

is

a

I t

is

first

It

Limit

current

ply

will

on until

J return

output

16.2V).

OONvENnCIIIAL

CURRENT

LIMIT

i552A-B-4314

Sectiull

II

If the latter occurs, the Diode Switch

is

effectively closed

and the power supply goes into a Foldback Current Limit

condition.

In

this condition the Current Limiting Transistor

is

controlled

by

tile power supply

outpu

t Voltage.

As

tile

output voltage decreases, the shunt current

is

increased.

UNA£OULATEO

DC

~~~f~

==;;-'

OONVENTlONAl

CUARENT

LIMITER

1-

-iii~T~~i~\~-----

1

'

I'

\ :

f"

R(

:j,L!L

A

T"[C

f--

i

---.-wY-..---

-+--

-""""

~

WJl

~

J

T

i 32<

I ,

L

__

____

_ _

_____

...J

r-----

I

Figure

4-3.

Simplified

Schematic

of

Current

Limiting

Circuitry

4-5

WARNING

I

Maintenance

described

herein

is

performed

with

power

supplied

to

the

instrument,

and

pro

-

tective

covers

removed.

Such

maintenance

should

be

performed

only

by

service-trained

personnel

who

are

aware

of

the

hazards

in-

volved

(for

example,

fire

and

electrical

shock).

Where

maintenance

can

be

performed

without

power

applied,

the

power

should

be

removed.

Model

654A Section V

SECTION

V

MAINTENANCE

5-1.

INTRODUCTION.

5-2.

This section contains maintenance and service

information for the

-hp-

Model

654A Test Oscillator.

Included are performance checks and adjustment and

calibration procedures.

5-3.

Tabl

e

5-1

lists the equipment required to properly

maintain the

Model

654A. If the recommended model

is

not available. any instrument that has specifications equal

to, or better than . the required specifications may

be

used.

5-4.

PERFORMANCE

CHECKS.

5-5

The performance checks are in-cabinet tests (except

where noted) to cOlllpare the performance

of

the

Mod

el

654A with the specifications

given

in

Table I-I. These

checks

Illay

be

used

for incoming inspection. periodic

maintenance and

for

performance checks after a repair. The

Performance Check Test card

at

the end

of

Section V may

be

cut

out,

and used

as

a permanent record of the

instrument's performance during incoming inspection.

It

is

recommended t hat performance checks and, if necessary.

calibration

be

performed every 90 days.

5·

6.

FREOUE'NCY

CHECKS.

5-7.

FREQUENCY RANGE CHECK.

a.

Connect

all

electronic counter to the 654A rear

panel COUNTER OUTPUT.

b. Set the 654A controls

as

follows :

FREQUENCY RANGE

......

. .

...

XIO

FREQUENCY

dial.

. . .

...

Extreme clockwise

c. The counter should indicate a period average

of

lOOms

or

greater. verifying a frequency

of

10Hz,

or less, at the lower end

of

the frequency range.

d.

Set the FREQUENCY RANGE switch to XIM and

FREQUENCY

dial

to

its

extreme

counter-clockwise postiton. The counter should

indicate a frequency

of

10MHz, or greater,

verifying a frequency of at least 10MHz at the

upper end

of

the frequency range.

e. Perform the Frequency Adjustments (Paragraphs

5-47 through 5-57) if the tolerances are not met.

5-8. FREQUENCY ACCURACY CHECK.

a.

Connect

an

electronic counter to the 654A rear

panel COUNTER OUTPUT.

b.

Set the 654A controls

as

follows:

FREQUENCY RANGE

..

...

. .

..........

XIO

FREQUENCY dial

........................

1

c. Verify frequency accuracy using the settings and

tolerances

given

in

Table 5

-2.

Use

t

he

period

average setting on the counter for frequencies

below I k

Hz

and

use

the frequency setting for

frequencies above I kHz .

d. Perform the frequency adjustments (Paragraphs

547

through 5-57) if the tolerances are not met.

5·9.

AMPLITUDE

ACCURACY

CHECKS.

(See also Table 3-1, Page 3-1).

5-10 .

SO

UNBAL AMPLITUDE ACCURACY.

a.

Connect the equipment

as

shown

in

Figure 5-1.

Use

the 50 ohm Feedthrough termination which

should

be

connected directly to the 654A output

connector.

b.

Set the 654A controls

as

follows:

FREQUENCY

dial..

..

....

..

I

FREQUENCY RANGE . , . , .

XI

K

OUTPUT LEVEL dBm

........

. .

".

. + I 0,0

IMPEDANCE

.....

....

..

.......

50 UNBAL

AMPLITUDE

..

. .

...

..

.. .. ..

Adjust

for

OdBm

on 654A meter.

c.

The ilC voltmcter iIHJication should

be

betwecn

.7000 V

rms

allLl

7

1.:11

V

rnl

S verifying

an

abso-

lute

level

of+

10

dBnl. +/

-1'

,"

d.

If the tolerances are not met perform

th

e Meter

Tracking and Amplitude Control Adjustments

of

Pmagraphs 5-58 through 5-60.

5-11. 75 UNBAL AMPLITUDE ACCURACY.

a.

Perform the procedure

of

Paragraph 5-10 except:

instep

a.

Use

the

75

ohm feedthrough

termination;

5-1

5-

2

Section V

Model

654A

Table 5-1. Required Test Equipment

INSTRUMENT

TYPE REQUIRED CHARACTERISTICS RECOMMENDED MODEL

Frequency

10

.00Hz to 1000MHz

El

ec

tronic -hp- Mude l 5245L

Countcr P

er

iod : 1.000 ms tu 100

.Oms

.

El

ec

tron

ic

Counter.

Ran

ge:

.9999V

rill

s and 9.999V

rms

full sca

le

.

-lIp-

,"Iudel J

--lS

OB

Vllllillcicr

AC

Di

gil

al

Mulli/\lI1cli

l)

n

Mel

cr

wil

li

OPT

00

I

A

cc

ur acy:

al

least . I 'If

of

reading

at

I kHz .

Wav

e

Fr

eq

uency Range I

MHz

III

22MHz.

-hr

· Model H05-31

2A

Analy

zc

r

Mu

st

be

cu mpatib

le

w

it

h Tr

ack

in

g O

sc

illat or.

Wa

ve

Analyzer.

(N

ute: the

H0

5-3

I

2A

is

required on

ly

for

di

stortion checks,

otherwise a standard -hp- 3 I

2A

can

be

used .)

Must

be

cap

abl

e

of

ex

pandi ng wave analyzer

Tr

ac

kin g

-hp-

Model 3

13A

Os

cillator metcr indi

ca

tion to resolve 0.05dB. T racki

ng

O

sc

illat o

r.

Distortion Sen

si

tivit

y:

gr

eater than 46dB.

-hp-

Modcl 333A

Analyzer

Di

sturti un

Fr

eq

uency range · 10Hz to 600kHz.

Di

stortion Analyzer.

-hp- Model 46 I A Gene

ral

F requcncy range : I kHz to 10MHz.

Amplifier Gain: 40dB .

Purpose Amplifi er.

-hp- Model

400E

Voltage ra

nge

I .00

mV

rm

s to I .

OOV

rms

Frequ

en

cy

ra

ng

e:

10Hz to

10MH

z.

AC

Vo

ll

nlcter

AC

Vo ltmcle

r.

(dB

sca

le

s referenced

to

I

mW

int o

600

o

hm

s).

Ran

ge:

IOuV to 10mV .

-hp-

Mod

el 4 I

9A

V

ul

t meter

DC

Null

DC

Null

Vo ltmetcr.

A

cc

uracy : +/-2

'7<

of

full

sc

al

e.

-

hp-

Model 4

27

A

Input Impedan

ce

10

mego hms.

Range 0. 1

V to 100V .

DC

Voltmete r

Multi-F unc tion Mete

r.

Oscill

os

cope

Sen

si

ti

vity : 5mV!cm. -hp-

Model

180 A

Bandwidt h :

dc

to 50MH

z.

Oscilloscope with 1

80

I A

and I 820A plug-ins.

Fe

ed

thruu

gh

Feed-Thru

Termina

ti

ng

Resi

stan c

e:

(a) -hp- Model 1I04SC

(3

) 50 u

hm

s +

/-25'

i[

Re

s

i

s

t

~

lnc

e

(b)

75

ohms

+/

-.25

(;

~

(b) -

hr

-

Mod

el 1I094A

All

cn

uat ors

Fr

equ e

ncy

r

an

gl'

:

10H

z to

10Mf-I

z (with known

acc urac y

at

10kHz_

300kJlz and 10MHz)

Al

te nuation

rall

gc:

VHF

Altenu ators

(a)

-hp-

Mod

el

35

5C

(a) 9dB

in

IdB steps .

(b) -hp- Model

35

5D

(b) 90dB

in

I

OdB

steps

Thef1l1al

Fr

equency range :

10H

z

to

1

0MH

z.

Cunvert e

rs

Input

at

least +IOdBm into rat

ed

input impedan ce.

Inp

ut

impedance :

(a) 50 o hms_ unbalanced.

(b)

75

o

hm

s, unbalanced .

( c)

13

5 ohm

s,

bal

an

ce

d.

(d) 150 ohms, balanced .

(

e)

60

0 ohm

s,

balan

ce

d.

Thermal Convert e

rs

(a) -hp Model

1I0

50A

(b) -hp - Mo

del

HOI

-I 1050A

(c) -

hp-

Model

HI

I

-I

1050A

(d)

-hp-

Model H

12-1

1050A

(

e)

-hp- Model HIO-11050A

Bl"C

to

Bin

ding

P

os

t Adap(er

-hp-

Mod

el 10110A

(2

required)

R

es

istors . l iS

W,

metal

film

.

(a)

75

o hm

s_

.25

% (t

wo

requ

ire

d) .

(b)

13

5 ohms , . I 'It

(f

o

ur

required).

(d

300 oh m

s,

. I r

ic

(two required) .

-hp-

Part

No:

0698-6262

0698-7364

0698 -6295

Not

e.

Th e fu

ll

ow

in

g items

ar

e not com m

erC

ially a

va

ilable

bUI

ca

n be easily co

nsl

ruclcu . Icfe r to the figures

hsted

fo

r schemalics and part, lis

ts

.

DC

Refere

nc

e

Su

ppl

y

Fi

gu

re

54

No t

e:

The foll ow

in

g a

re

useful optional item

s.

1)

.Jumper

ca

bl

e,

8

in,

-hp -Part No. 10502-600 1

(2 required,

se

e Para gra

ph

5-30a)

75 uhm

[()

50

oh

m Illlpcu a

ncc

Co

nvcnCf

B

ala

n

ce

B

ox

Fi

gure 5-7

Fi

g

ur

e

5-9

2 )Sin e

-Wa

ve

Signal Generator : may

be

r

eq

uir

ed

for

troubt

es

hoo tln g

(Refer to

Par

ag

raph s 5

-7

9 and 5

-8

3.)

10MHz Low-

Pass

Filtcr

ligureS-12

HP 654A Service manual

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