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D

SECTION 1

FEATURES

AND

SPECIFICATIONS

•

1-1.

Physical

and

electrical

specifications

1-

2.

Control

features

and

facilities

1-3.

Specifications

1-4.

Controls

and

input

terminals

1-5.

Notes

on

controls

and

terminals

SECTION 2

OPERATION

SECTION 3

APPLICATION

3-1.

General

3-2.

Waveform

investigation

3-3

.

Waveform

display

3-4.

Lissajous

patterns

3-5.

Servicing

TV

receivers

SECTION 4 MAINTENANCE

4-1.

General

4-2.

Access

to

chassis

4-3.

Vertical

amplifier

adjustments

4-4.

Horizontal

amplifier

adjustments

4-5

.

Frequency

compensation

Vertical

channel

Horizontal

channel

4-6.

Calibration

voltage

adjustment

4-7

.

Horizontal

TV

sweep

trimmer

adjustment

4-

8.

Troubleshooting

4-9

.

Tube

Replacement

4-10.

Fuse

Replacement

1 COPYRIGHT ©

1969

EICO

ELECTR

ON

IC

INST

RUMENT

COMPANY,

I

nc

.

-

SECTION

1

FEATURES

AND

SPECIFICATIONS

1-1. PHYSICAL AND

ELECTRICAL

SPECIFICATIONS

a.

DC

to

8 MHz (+l,

-5

dB) o

f.

the

vertical

amplifier

is

more

than

enough

needed

for

both

color

and

monochrome

TV

service.

The

horizontal

amplifier

frequency

response

is

from

DC

to

1 MHz

(+l, - 3 dB).

Both

amplifiers

feature

push-pull

amplification

throughout

for

minimum

distortion,

while

the

direct-coupled

design

eliminates

low-frequency

phase

shift

or

response

fall

off.

This

DC

design

also

permits

making

true

voltage

measurements

of

any

waveform.

b.

A

pair

of

zener-controlled

voltage

reference

sources,

and

their

associated

adjustment

poten-

tiometers

provide

an

accurate

source

of

calibration

voltages

for

both

the

horizontal

and

vertical

channels.

c.

Using

a

1500-volt

accelerating

potential

provides

a

sharp,

bright,

trace

free

from

blooming.

A

mu-metal

CRT

neck

shield

minimizes

the

effects

of

external

magnetic

fields.

d.

Distortionless

vertical

and

horizontal

gain

and

drift-free

V & H

positioning

up to

many

times

the

actual

viewing

screen

diameter.

e.

Automatic

sync

limiter

and

amplifier

provides

rock-steady

sync

signals

for

the

sweep

circuits.

f.

Full

retrace

blanking

is

provided

to

remove

objectionable

background

clutter.

g.

Edge-lit

calibration

grid

on a

green

filter

screen

has

its

illumination

level

controlled

by

front

-

panel

control.

h.

Human-engineered

front

panel

features

all

controls

in

logical

order

and

grouped

for

easiest

use.

i.

Front-panel

switches

enable

switching

either

vertical

or

horizontal

channel

to

either

AC

or

DC

response.

j.

Heavy-duty

power

supply

reduces

generated

heat

and

makes

for

a

long

component

life.

k.

Each

channel

is

provided

with

its

own

internal

voltage

calibrator.

1-2.

CONTROL

FEATURES

&

FACILITIES

a.

Both

the

vertical

and

horizontal

channels

use

a

four-position,

frequency

compensated

input

decade

attenuator,

plus

a

calibration

position.

A

concentric

gain

control

is

effective

in

all

positions,

including

the

calibration

position.

A

slide-switch

is

provided

for

each

channel

to

select

either

direct

coupling

(DC)

or

capacitive

coupling

(AC).

b.

Both

amplifiers

can

be

balanced

at

any

time

via

a

pair

of

balance

controls

that

can

be

adjusted

through

a

pair

of

small

holes

on

the

front

panel.

c.

The

horizontal

sync

selector

permits

selection

of

either

internal

positive

or

negative,

external,

60

Hz,

or

provides

a

60-Hz

sweep.

A

sixth

position

passes

an

external

signal

into

the

horizontal

amplifier.

d.

Sweep-range

selection

from

10

Hz to

100

kHz

in

four

overlapping

ranges,

plus

a

preset

TV

vertical

and

horizontal

sweep

positions

(30

and

7875 Hz

respectively).

A

concentric

sweep

vernier

permits

adjustment

within

any

range.

e.

Scale

illumination,

and

CRT

intensity,

focus,

and

astigmatism

are

all

controlled

by

front

panel

controls.

f. An

intensity

modulation

input

is

provided

on

the

rear

panel.

2

.L-

"·

or

.D'-'.l.l'

.l\.,i-1

.

.l

lVl~.:>

a.

Vertical

amplifier:

Frequency

response:

DC

to

8 MHz (+l, - 5 dB)

Sensitivity:

12

mV

per

cm

r.

m.

s.

Input

impedance:

1

megohm

shunted

by

35

pF

Calibration

voltage:

z

ener-controlled

200

mV

peak-to-peak,

±1%

Input

scale

attenuation:

. 05, .

5, 5,

and

50

volts/cm

b.

Horizontal

amplifier:

Frequency

response:

DC

to 1 MHz,

1-l,

-3

dB

Sensitivity:

17

mV

per

cm

r.

m.

s.

Input

Impedance:

1

megohm

shunted

by

35

pF

Ollibration

voltage:

zener-controlled

500

mV

peak-to-peak,

±

1%

Input

scale

attenuation:

. 05, . 5,

5,

and

50

volts/cm

c.

Sweep

r

anges

:

10-100 Hz,

100

Hz-

1 kHz, 1-10

kHz,

10-100 kHz,

plus

fixed

TV

vertica1(30

Hz),

and

horizontal

(7875 Hz).

d.

Intensity

modulation:

3

volts

r.

m.

s.

blanking

Input

impedance

2. 2

megohms

e.

Tube

complement:

l-12AZ7, l-12AU7, 2-6AU8, 2-12BY7,

3-6B

L 8; 3

silicon

rectifiers,

1

silicon

HV

rectifier,

2

zener

diodes,

5DEP1

CRT.

f.

Power

supply:

ll7

-

volts

AC,

approximately

140

watts

g.

Size:

12

1/2

high x 8 1/ 2

wide

x

17

1/2

deep

h.

Wei

ght:

27

lb

s.

1-

4.

CONTROLS AND

INPUT

TERMINALS

The

Model 465

has

its

controls

and

input

terminals

grouped

in

logical

arrangement

as

for

use.

All

controls

for

either

channel

are

vertically

grouped

on

each

side

of

the

front

panel,

th

e

sync

and

sweep

controls

are

in

the

middle

segment,

while

the

CRT

controls

are

grouped

alongside

the

CRT

screen.

a.

The

AC

pow

er

on/off

switch

is

located

on

the

SCALE

ILLUMination

control

and

is

operated

by

rotating

this

control

clockwise

from

the

OFF

position

.

This

also

turns

up

the

scale

illumination.

3

b.

The

INTENSITY, FOCUS,

and

ASTIGmatism

controls

determine

the

brightness

and

sharpness

of

the

visible

trace.

The

INTENSITY

control

determines

the

brightness,

while

both

FOCUS

and

ASTIGMATISM

determine

the

sharpness.

These

three

controls

interact

to

a

slight

extent,

therefore,

a

change

in

any

control

setting

may

require

a

change

in

all.

c.

In

both

amplifier

groupings,

the

topmost

control

(V

/CM)

selects

the

amount

of

input

attenuation

,

in

conjunction

with

its

concentric

gain

control.

In

both

cases,

the

calibration

voltage

position

is

indicated

in

red.

Both POSITION

controls

adjust

the

location

of

the

trace

on

the

screen.

The

HORIZ

position

control

moves

the

trace

to

the

right

or

left,

while

the

VERTICAL

control

adjusts

the

trace

up

and

down.

Each

input

attenuator

provides

four

degrees

of

attenuation;

resulting

in

either

. 05, . 5, 5,

or

50

volts-per-cm

deflection.

Each

input

is

obtainable

with

either

AC

or

DC

coupling

by

operation

of

either

AC-DC

switch

located

near

the

bottom

of

each

channel

section

.

The

use

of

direct

coupling

(UC)

prevent

phase

shifts

and

amplitude

distortions

of

low-frequency

waveforms

and

also

provides

a DC

reference

line

to

be

established

for

accurate

amplitude

measurement.

AC

coupling

is

used

when

observing

a

small

a.

c.

signal

superimposed

on

a

relatively

large

d.

c.

voltage

.

At

the

CAL

position,

the

square-wave

calibration

voltage

is

fed

directly

to

the

amplifier,

bypassing

the

decade

attenuator

switch,

but

not

the

GAIN

control.

By

setting

the

vertical

GAIN

control

for

a

vertical

trace

size

of

four

major

divisions

(4

cm),

the

basic

50 mV

/cm

sensitivity

is

obtained

when

setting

the

VERT

AMPLIFIER

V/cm

switch

to

the.

05

position

and

sensitivities

of.

5, 5,

and

50

volts/cm

at

the

other

three

positions

provided

that

the

VERT

AMPLIFIER

V

/CM

GAIN

control

is

not

changed.

By

setting

the

HORIZ

AMPLIFIER

V

/CM

switch

to

the

CAL

position,

and

setting

the

GAIN

control

for

a

trace

of

10

divisions

long

(10

cm),

the

basic

50 mV

/cm

sensitivity

is

obtained

for

the

horizontal

channel

when

resetting

the

HORIZ

AMPLIFIER

V/ CM

switch

to

the

.

05

position,

and

sensitivities

of . 5, 5,

and

50

volts/cm

at

the

other

three

positions

provided

that

the

HORIZ

AMPLI-

FIER

V/ CM GAIN

control

is

not

changed.

d.

Both

vertical

and

horizontal

channels

GAIN

controls

can

be

adjusted

for

any

desired

signal

height,

or

trace

length,

if

accurate

calibration

is

not

needed.

e.

Both

VERT

AMPLIFIER

and

HORIZ

AMPLIFIER

lNPUT

and

GND

terminals

will

accept

standard

scope

connectors,

probe

leads,

or

plain

wires.

f.

The

SYNC

SELECTOR

switch

has

four

sync

positions

to

permit

sync

selection

for

the

sweep

generator.

At

the

60Q

position,

an

a.

c.

signal

of

power-line

frequency

is

taken

from

the

power

supply

and

applied

to

the

sweep

generator

to

synchronize

it

at

power-line

frequency.

At

the

EXT

position,

an

external

signal

applied

to

the

HORIZ

AMPLIFIER

INPUT

binding

post

syncs

the

sweep

generator.

At

both

"+-"

and

"-"

positions,

the

synchronizing

signal

is

derived

internally

from

the

vertical

(signal)

amplifier.

At"+-",

synchronization

occurs

on

the

positive-going

edge

of

the

applied

input

signal.

At"-",

from

the

negative-going

portion

of

the

applied

vertical

channel

signal.

At

the

60Q HORIZ

position,

an

a.

c.

voltage

is

taken

from

the

power

supply

and

used

as

the

input

to

the

horizontal

amplifier

to

form

the

sweep.

In

the

EXT

HORIZ

position,

the

signal

applied

to

the

HORIZ

AMPLIFIER

INPUT

binding

post

forms

the

sweep.

g.

The

SWEEP

RANGE

switch

selects

the

frequency

band

over

which

the

concentric

vernier

(VERN)

control

can

be

varied

for

frequency

adjustment

of

the

internal

linear

sweep,

or

the

preset

VERT

TV

or

HORIZ

TV

positions,

designed

to

eliminate

the

need

for

repeated

adjustment

of

the

SWEEP

RANGE

switch

when

working

on

TV

sets

that

use

two

widely

spaced

frequencies

for

vertical

and

horizontal

circuits.

In

the

four

numbered

positions,

the

numbers

above

the

positions

markers

indicate

the

upper

and

lower

frequency

limits

of

the

band

(approximately),

for

that

particular

position.

The

convenience

provide

by

the

VERT

TV

and

HORIZ

TV

positions

is

as

follows:

if

at

the

VERT

TV

position,

the

SWEEP

RANGE

VERNier

is

set

to

display

two full

cycles

of

a

60

Hz

signal

to

obtain

a

sweep

frequency

of

30 Hz,

placing

the

SWEEP

RANGE

switch

in

the

HORIZ

TV

position

will

result

in

an

automatic

7875

Hz

display

without

any

adjustment

of

the

VERNier

.

4

11.

rtu

externa1

vonage

tor

the

purpose

of

int

ensity

(Z

axis)

modulation

may

be

applied

between

tbe

rear-panel

intensity

modulation

pin

jack

and

chassis

ground.

Do

not

apply

more

than

3

volts

peak

to

this

input

or

the

life

of

the

CRT

may

be

greatl

y

shortened.

Do

not

allow

the

CRT

grid

to

swing

positive

(indicated

by

a

noticeable

defocussing

of

the

trace).

1-5. NOTES ON CONTROLS AND TERMINALS

a.

Proper

trace

definition

will

be

obtained

only

if

the

FOCUS

and

ASTIG

controls

are

correctly

adjusted,

and

the

scope

is

not

operated

in

strong

magnetic

fields

such

as

those

found

near

large

power

transformers,

radio

transmitters,

and

power-generating

equipment.

These

strong

magnetic

fields

may

distort

the

electron

beam

that

produces

the

trace.

b.

A

sharply

focussed

line,

or

a

small

dot

of

high

intensity,

should

not

be

permitted

to

remain

stationary

on

the

screen

for

any

period

of

time

(more

than

a

1/2

minute

or

so)

or

the

screen

may

be

burned.

A

trace

of

excessively

high

intensity

will

burn

the

screen

in

3 to 5

minutes,

therefore,

do

not

keep

the

INTENSITY

control

turned

up

for

extended

periods

of

time.

Burned

portions

of

the

screen

will

no

longer

fluoresce

and

are

useless

for

observation.

If

it

is

required

to

have

a

fixed

trace

on

the

screen

for

a

long

period

of

time,

reduce

the

intensity

of

the

trace

to

minimum.

c. When

either

AC-DC

switch

is

placed

in

the

DC

position,

the

d. c.

component

of

any

signal

fed to

U:e

amplifier

w

ill

be

amplified

along

with

the

a.

c.

component

of

the

signal.

The

direction

of

trace

movement

is

UP

for

a

positive

voltage

and

DOWN

for

a

negative

voltage.

Therefore,

when

going

from

observation

of a

pure

a.

c.

signal

to

one

containing

d.

c.

(or

vice

versa),

it

may

be

necessary

to

use

the

POSITION

control

to

bring

the

trace

back

on

the

screen.

Any d. G·

component

has

no

effect

when

the

AC-DC

switch

is

in

the

AC

position.

d. A

trace

can

be

expanded

horizontally

and

/

or

vertically

to

several

times

full

screeh

without

dis-

tortion

by

using

the

amplifier

V

/CM

switch

and

concentric

GAIN

control.

Likewise,

'

trace

positioning

is

several

times

screen

diameter

to

permit

examination

of

any

portion

of

the

expanded

trace.

e. An

independent

DC

BALance

control

is

provided

for

each

channel.

These

are

accessible

through

small

holes

on

the

front

panel.

When

they

are

properly

adjusted,

there

should

be

no

shifting

of

the

trace

(no

signal

applied)

when

the

GAIN

control

is

rotated

from

minimum

to

maximum.

Detailed

alignment

will

be

given

in

the

MAINTENANCE

section.

f.

The

vertical

channel

voltage

calibration

developes

a

negative-going

signal.

This

means

that

if

the

top

of

the

calibration

square

wave

is

set

to

the

horizontal

center

line

of

the

calibration

grid,

(using

the

vertical

channel

POSITION

control),

the

horizontal

center

line

becomes

the

"zero

center"

for

the

calibration

grid

(assuming

that

the

DC

balance

is

correct).

Under

these

circumstances,

direct

read-

ing of AC, DC,

or

AC

superimposed

on

DC

voltages

can

be

made.

The

horizontal

center

line

is

zero

voltage,

while

trace

points

above

the

center

line

are

positive,

and

below

the

center

line

are

negative.

Once

calibration

has

been

made,

then

operation

of

the

V

/CM

control

can

be

used

to

determine

the

signal

voltage

level.

Pure

DC

voltages

are

determined

by

noting

the

distance

above

the

horizontal

center

line

(for

positive

signals)

or

below

the

center

line

for

negative

levels,

and

multiplying

the

displacement

in

cm

(smallest

grid

division

is

2

mm,

major

division

is

1

cm),

by

the

sensitivity

of

the

particular

V

/CM

switch

position.

For

example

-

an

unknown

DC

voltage

applied

to

the

VERT

AMPLIFIER

INPUT

and

GND

binding

posts

at

the

.

05

position

of

the

V

/CM

switch

causes

a

downward

trace

displacement

of 2

1/2

small

grid

division

(4

1/2

mm).

Since

the

deflection

is

downward,

the

voltage

is

negative.

As

the

sensitivity

is

50

mV

/

cm

in

the

.

05

position,

the

DC

voltage

is

25

mV.

AC

waveforms

with

or

without

a

DC

component

can

be

read

as

to

absolute

voltages

at

any

point,

and

including

the

value

of

any

DC

component.

For

example

-

an

unknown

voltage

applied

to

the

vertical

channel

at

the

. 5

position,

displays

a

waveform

having a

positive

peak

4

major

divisions

above

the

horizontal

center

line

and

a

negative

peak

2

major

divisions

below

the

horizontal

center

line.

As

the

sensitivity

at

the . 5

position

is

500

mV

/cm,

the

positive

peak

is

2

volts

and

the

negative

peak

is

1

volt

(3

volts

peak-to-peak).

When

the

AC-DC

switch

is

in

the

AC

position,

the

positive

peak

moves

1

1/2

major

divisions

(7

1/2

minor

divisions)

downward

so

that

the

positive

peak

is

now

only

2

1/2

major

divisions

(12

1/2

minor

divisions)

above

tre

horizontal

center

line.

Since

1

major

division

is

500

mV

at

the

. 5

position,

the

DC

component

of

the

voltage

is

11/2

cm

x 500

mV

/cm

or

750

mV

and

positive.

If

the

signal

under

observation

is

a

sine-wave

only,

the

r.

m.

s.

value

may

be

calculated

by

dividing

the

peak-to-peak

value

by

2. 8.

5

SECTION

2

OPERATION

To

obtain

the

best

r es

ults

with

your

scope,

it

is

advisable

to

beco

me

acquainte

d

with

the

functions

and

correct

usa

ge of the

panel

controls

and

terminals

,

by

mak

i

ng

some

si

mple

t

ests

.

These

tests

will

also

assure

you

that

the

instrument

is

in

perfect

wor

ki

ng or

der.

Do

not

a

tt

em

pt

this

procedure

with

kits

before

all

fina

l

checks

have

been

completed

and

all

initial

adjustments

have

been

completed

as

explained

in

the MAINTENANCE

section.

a.

Set

the

SC

ALE ILLUM

control

to

OFF,

INTENSITY, FOCUS,

and

ASTIG to

the

center

of

their

range

.

b. On

the

VERT

AM

PLIFIER

section,

set

the V

/CM

s

wit

ch

to 50 and

the

GA

IN

cont

r

ol

fully

counter-

clockwise

.

Set

POSITION

near

the

center

of

its

range

.

c. On

the

HORIZ A

MPLIFIER

section

,

set

the

V

/CM

switch

to .

05

and

the

GAIN

cont

rol

fully

counterclockwi

se.

The

POSITION

control

should

also

be

set

about

half

way

.

d.

Set

the

S

YN

C

SELECTOR

control

to

EXT

. HORIZ.

Set

the

SWEEP

RANGE

and

VERN

control

to

any

position.

e.

Insert

the

power

cord

into

a

nominal

ll7-volt,

60

-H

z

outlet.

WARNING

This

instrument

will

not

operate,

and

will

be

seriously

damaged,

if

connected

to

an

y

ot

her

type of

power

sou

r

ce

(such

as

d.

c.,

25-Hz,

200/240

-

volts

a. c. ),

unless

fitted

wi

th

spe

ciali

zed

power

supply

components.

f.

Rota

te

the

SCALE

ILLUM

off

the

OFF

position

and

note

the

click

as

the

associated

switch

is

operated.

The

small

pilot

lamp

at

the

bottom

of

the

fron

t

panel

should

glow.

The

two

scale

illum

i-

natfon

lamps

will

start

to

glow

and

this

glow

can

be

increased

by r

otating

the

SCALE

ILLUM

control

more

clockwise.

Set

the

scale

illumination

at

a low

le

v

el.

g. As

the

unit

warms

up, a

bright

spot

should

appear.

If

the

spot

does

not

appear,

it

may

be

necessary

to

rotate

the

INTENSITY

control

slightly

more

clockwise,

and

possibly

make

some

ad-

justment

to

both

POSITION

controls.

h.

Using

the

POSITION

controls,

center

the

spot

on

the

screen.

i.

Adjust

the

FOCUS

and

ASTIG

controls

for

the

sharpest

image

. Note

that

there

is

some

inter

-

action

between

the

INTENSITY, FOCUS,

and

ASTIG

controls

,

therefore,

all

three

will

have

to

be

ad-

justed

for

the

sharpest

results.

j.

Set

the

SYNC

SELECTOR

switch

to

either"+"

or

"- ".

Advancing

the

HORIZ

AMPLIFIER

GAIN

control

clockwise

should

cause

the

dot

to

extend

into

a

horizontal

line.

This

is

the

horizontal

linear

sweep.

Reset

the

SYNC

SELECTOR

to

EXT

HORIZ

and

note

that

the

trace

drops

back

to

a dot. Any

signal,

even

touching

the

HORIZ

AMPLIFIER

INPUT

terminal

,

will

cause

a

trace

to

appear

whose

length

is

a

function

of

the

HORIZ .

AMPLIFIER

V

/CM

switch

and

GAIN

control.

k.

Set

the

SYNC

SELECTOR

back

to

60n

HORIZ.

The

length

of

the

horizontal

line

seen

on

the

screen

is

also

a

function

of

the

setting

of

the

HORIZ

AMPLIFIER

V

/CM

switch

and

its

associated

GAIN

control.

This

trace

is

a

60-Hz

sine

sweep

and

is

used

for

certain

set

alignments.

1.

Set

the

SYNC

SELECTOR

to "+-",

and

HORIZ

AMPLIFIER

V/ CM

and

GAIN

controls

for

a

useful

long tr

ace.

Place

the

SWEEP

RANGE

switch

in

the

10

-

100

position,

and

the

associated

VERN

control

fully

counterclockwise.

m.

Set

the

VERT

AMPLIFIER

V

/CM

switch

to

the

CAL

position.

Adjust

the

VERT

and

HORIZ

AMPLIFIER

GAIN

control

until

the

square-wave

pattern

covers

about

two

thirds

of

the

screen.

Center

the

pattern

using

the

POSITION

controls.

Lock

the

pattern

on

the

trace

by

adjustment

of

the

SWEEP

RANGE VERN

control

until

a

single

square-wave

is

displayed

on

the

screen,

and

remains

stationary

.

6

NOTE:

In

rotating

the

SWEEP

RANGE VERN

control,

the

pattern

slows

down

as

certain

critical

frequencies

are

approached,

and

then

it

appears

to

reverse

direction

when a

critical

frequency

is

passed.

At

these

critical

frequencies,

a

clear

square-wave

pattern

can

be

discerned.

These

criti-

cal

sweep

frequencies

are

sub-multiples

of

the

signal

frequency,

or

the

signal

frequency

itself

(when

only

one

cycle

is

displayed).

The

pattern

may

be

locked

in

at

any

sub-multiple

of

the

signal

frequency

when

it

is

desired

to view

more

than

one

cycle

of

the

applied

signal.

The

sweep

frequency

is

equal

to

the

signal

frequency

divided

by

tl

ie

number

of

complete

cycles

displayed

on

the

screen.

For

example

-

if

two

complete

cycles

of

the

60-Hz

signal

are

displayed,

the

sweep

frequency

is

30

Hz.

At

very

low

sweep

frequencies,

flickering

of

the

trace

is

normal

due to

the

slow

writing

speed

of

the

electron

beam,

and

the

persistence

of the

screen.

Taken

together,

these

may

be

insufficient

to

cause

the

beam

motion

to

blend

into a

clear

fixed

image.

n.

Adjust

the

SWEEP

RANGE VERN

until

the

single

square

wave

pattern

locks

on

the

positive-going

leading

edge,

which

should

not

be

visible.

Placing

the

SYNC

SELECTOR

in

the

"-"position

should

cause

the

pattern

to

move

over

until

sync

takes

place

on

the

negative

transition.

o.

If

it

is

desired

to

observe

the

operation

of

the

intensity

modulation

facility,

connect

the

output

of

an

audio

generator

to

the

rear

panel

intensity

jack

and

front

panel

GND.

Be

sure

that

the

INTENSITY

control

is

set

no

higher

than

is

necessary.

Set

the

audio

generator

to

600 Hz

and

bring

up

the

generator

o

utput

until

the

displayed

single

pattern

breaks

up into

segments.

Do

not

increase

the

generator's

ou

tput

above

the

level

required

to do

this.

Fine

adjust

the

generator

frequency

carefully

until

the

seg-

me

nt

s

become

stationary.

If

the

segm,ents

are

counted,

it

will

be

found

that

there

are

10.

This

indi-'

cat

es

that

the

ratio

between

the

frequency

of

the

intensity

modulation

(audio

generator)

and

the

vertical

ampl

ifier

input

(in

this

case

60 Hz)

is

600/60

or

10.

Therefore,

the

intensity

modulation

can

be

used

for

introducing

timing

markers

on

the

trace,

or

for

determining

the

frequency

of

an

unknown

signal.

CAUTION

When

using

the

INTENSITY

modulation,

the

INTENSITY

control

should

first

be

set

at

minimum

(counterclockwise}

and

then

turned

clockwise

just

enough to

obtain

normal

intensity.

If

this

is

done,

the

possibility

of

applying

excessive

intensity

modulation

signal

voltage

will

be

minimized.

SECTION

3

APPLICATION

3-1. GENERAL

The

oscilloscope

are

the

electronic

"eyes"

of

the

technician

and

enable

him

to

see

waveforms

that

are

totally

invisible

to

his

normal

eyes.

The

scope

is

capable

of

displaying

high-speed

electrical

waveforms

of

both

continuous

and

transient

nature

from

a few

cycles

per

second

to

many

millions

of

cycles

per

second.

3-2.

WAVEFORM INVESTIGATION When

the

output

of

the

scope's

internal

sweep

generator

is

fed

to

the

horizontal

channel,

the

pattern

on

the

CRT

screen

is

actually

a

graph

displaying

the

variation

with

time

of

the

instantaneous

amplitude

of

the

signal

applied

to

the

vertical

channel.

The

horizontal

sweep

time

can

be

varied

so

as

to

present

one

or

more

full

cycles

on

the

screen.

3-3.

WAVEFORM DISPLAY

It

is

generally

most

convenient

to

use

a

time

base

that

varies

linearly

with

time,

so

that

equal

intervals

of

time

are

represented

on

the

screen

by

equal

intervals

of

distance

along

the

horizontal

axis.

If

the

frequency

of

the

observed

signal

is

exactly

equal

to

the

sweep

frequency,

one

complete

vertical

channel

cycle

will

be

observed

on

the

screen.

If

the

frequency

of

the

applied

signal

is

twice

the

horizontal

sweep

frequency,

two

complete

cycles

will

be

seen

on

the

screen,

and

so

on.

Fig.

1

is

projection

drawing

of

a

simple

sine

wave

applied

to

the

vertical

channel

and

a

linear

(with time}

sawtooth

applied

to

the

horizontal

channel.

Fig.

2

is

a

similar

drawing

showing

the

re-

sultant

pattern

when

the

frequency

oi

the

sawtooth

is

one-half

that

used

in

Fig.

1.

In

both

figures,

7

points

that

occur

simultaneously

are

numbered

the

same.

The

circle

represents

the

CRT

screen.

If

simultaneous

projections

were

drawn

from

every

point

on

each

waveform,

the

intersections

would

trace

out

the

sine

waves

shown

within

the

circles.

The

sections

of

the

sawtooth

between

1

and

4 of

Fig.

1,

and

between

1

and

9 of

Fig.

2

are

the

sweep

sections

during

which

the

actual

CRT

display

is

produced.

The

sawtooth

sections

between

4

and

5 of

Fig.

1,

and

between

9

and

10

of

Fig.

2,

are

the

sections

during

which

the

electron

beam

is

returned

very

rapidly

to the

starting

point

at

the

left

of

the

screen.

This

return

tra

~

e

is

prevented

from

appearing

on

the

screen

by

a

built-in

blanking

circuit.

1......,__

I I

_/'I

l~I

I I I I

tlz:

4:

I I 1

TllEI:

21

3

60

SEC.

FIGURE

1

t

TIME

I

I

I

110

I

1

JO

SEC.

1~-

-...,.-~

FIGURE

2

3-4.

LISSAJOUS

PATTERNS:

Another

type

of

fundamental

pattern

is

obtained

when

both

the

vertical

and

horizontal

deflection

voltages

are

sine

waves

that

are

related

in

frequency

when one

frequency

is

a whole

number

of

times

greater

than

the

other;

or

when

one

frequency

is

a

simple

fraction

of

the

other.

When one

or

the

other

of

these

conditions

is

fulfilled,

stationary

closed-loop

patterns

are

obtained.

These

patterns

are

called

Lissajous

figures

after

a 19th

century

French

scientist.

They

are

parti-

cularly

useful

in

determining

the

frequency

ratio

between

two

sine

wave

signals.

If

the

frequency

of

one

signal

is

known,

the

frequency

of

the

other

signal

can

be

easily

determined

from

the

frequency

ratio.

Usually

the

known

signal

is

applied

to

the

horizontal

channel

and

the

unknown

signal

to

the

vertical

channel.

The

shape

of

the

pattern

changes

with

the

phase

relationship

between

the

known

and

unknown

signals.

For

example,

all

the

patterns

shown

in

Fig.

3 (and

those

intermediate)

are

possible

with

a

frequency

ratio

of

1:1

if

the

phase

differences

indicated

exist.

2: 1

3:

1 4

:1

1: 2

1:

3 1:4

I 0

\J

\

0

D°

45°

900

135°

1811"

OO@{XID8§~

FIGURE

3

FIGURE

4

In

general,

to

determine

frequency

ratio

from

the

Lissajous

figure,

count

the

number

of

points

of

tangency

to

horizontal

and

vertical

lines,

drawn

or

imagined

(see

Fig.

4).

Points

of

tangency

at

the

top of

the

figures

result

from

the

unknown

frequency

applied

to

the

vertical

channel.

Those

at

the

side

of

the

figure

result

from

the

known

frequency

applied

to

the

horizontal

axis.

V

axis

freq

H

axis

freq

V

pts

of

tangency

H

pts

of

tangency

As

an

example,

take

Fig.

4c,

which

shows

four

points

of

tangency

at

the

top

and

one

point

at

the

side.

This

indicates

that

the

unknown

frequency

applied

to

the

vertical

axis

is

four

times

the

known

frequency.

In

Fig.

4f, one

point

of

tangency

at

the

top

and

four

at

the

side

indicate

that

the

unknown

frequency

is

one-fourth

the

known

frequency.

8

A

square-wave

generator

such

as

the

E

IC

O Model 377

can

be

used

to

rapidly

check

amplifiers

for

frequency

response,

phase

shift,

transi

ent

r e

sponse,

deficient

design,

or

faulty

components.

AUDIO

GENERATOR

EQUIPMENT

~

TO

BE TESTEDr

~

SCOPE

FIGURE

5

~

~

-\b

-%-

_r;rr

~

~-

~

~-

FIGURE

6

First,

for

a

basis

of

comparison,

the

square

wave

output

from

the

Audio

Generator

is

directly

viewed

on

the

scope.

The

horizontal

sweep

of

the

scope

should

be

adjusted

so

that

at

least

two full

cycles

can

be

seen

on

the

screen.

(Fig.

6a

shows

one

full

cycle

of

a

perfect

square

wave).

The

scope

is

then

connected

to

the

output

of

the

amplifier

under

test

so

that

the

amplified

square

wave

can

be

viewed

on

the

screen.

Possible

output

wave

shapes

are

shown

in

Fig.

6b to

6i,

and

the

significance

of

each

waveshape

is

explained

below.

Fig.

6b

shows

"rounding"

of

the

leading

edge

of

square

wave.

This

indicates

a

drop

off

in

gain

at

high

frequencies.

"Rounding"

will

generally

be

observable

when

there

is

a

substantial

drop

in

the

gain

by

the

tenth

harmonic

(br

less)

.

Therefore

, if a 2KHz

square

wave

fed

to

the

amplifier

is

re-

produced

on

the

scope

without

"rounding",

the

amplifier

is

flat

to

10

x 2KHz =20KHz.

Fig.

6c

shows

the

effect

of

increased

low-frequency

gain

and

Fig.

6d

shows

the

effect

of

de-

creased

low-frequency

gain

of the

square

wave

frequency.

Fig.

6e

indicates

lowered

gain

at

a

narrow

frequency

band

.

The

effect

of

phase

shift

in

the

amplifier

is

shown

in

Figs.

6f

and

6g.

If,

at

low

frequencies,

there

is

phase

shift

in

the

leading

direction,

the

square

wave

will

be

tilted

as

in

Fig.

6f.

If

there

is

phase

shift

in

the

lagging

direction,

the

top

of

the

square

wave

will

be

tilted

as

in

Fig.

6g.

The

steep-

ness

of

the

tilt

is

proportional

to

the

amount

of

phase

shift.

Phase

shift

is

not

important

in

audio

ampli-

fiers,

although

the

ear

is

not

entirely

insensitive

to

it.

In

television

and

scope

amplifiers,

however,

phase

shift

should

not

be

tolerated.

Fig.

6h

shows

the

pulse

output

from

the

amplifier

that

results

when

the

square

wave

has

under-

gone

differentiation

.

This

will

happen

when

the

grid

resistor,

or

the

coupling

capacitor

is

too low

in

value,

or

if

the

coupling

capacitor

is

partially

open.

Lastly,

Fig.

6i,

shows

a

square

wave

with

damped

oscillations

following

the

leading

edge.

This

results

when a

square

wave

is

fed

to

an

amplifier

in

which

distributed

capacities

and

lead

inductances

resonate

to

produce

"shock

oscillations"

.

In

television

and

scope

amplifiers

it

may

result

from

an

undamp

ed

peaking

coil.

High-fidelity

audio

amplifiers

may

be

given

a

rapid

check

by

testing

first

with

a

square

wave

of

fundamental

frequency

not

less

than

3

to

4

times

the

low-frequency

limit

of

the

amplifier

(3dB

point),

and

then

with

a

square

wave

of

fundamental

frequency

which

may

be

anywhere

between

1/100 to 1/

10

of

the

high-frequency

limit

of

the

amplifier

depending

upon how

many

harmonics

are

considered

necessary

to

produce

an

acceptable

version

of

a

square

waveform.

Usually,

square

waves

of

fundamental

frequency

from

40 to 60 Hz

and

1000

to

2000

Hz

are

employed

to

cover

the

range

up

to

20, 000 Hz.

To

insure

correct

results,

the

following

is

suggested:

Connect

the

proper

value

of

load

across

the

amplifier

output

terminals;

use

low-capacitance

cable

for

connecting

the

generator

to

the

amplifier

input;

set

the

generator

output

to

an

ample

value

but

be

sure

not

to

overload

the

amplifier.

The

square-

wave

signal

is

fed

to

the

amplifier

input

and

the

scope

is

connected

across

the

amplifier

load.

Use

the

internal

linear

sweep

to

observe

the

waveform

. Note

that

tone

controls

have

a

very

marked

effect

on

square

wave

response

and

should

be

set

to

the

"flat"

positions

unless

it

is

desired

to

observe

their

ef-

fect.

Note,

also

, t

hat

low-fidelity

and

p.a.

amplifiers

will

not

reproduce

the

square

waveform.

Video

amplifiers

may

be

square

wave

tested

in

the

same

manner

as

described

for

testing

audio

amplifiers.

The

test

frequencies

might

be

60

Hz

for

the

low

end,

and

25, 000 Hz

for

the

high

end.

9