RCA WO-33A User manual

PRICE

ONE

DOLLAR

CATHODE-RAY

OSCILLOSCOPE

Type

WO-33A

• Specifications

•

Operation

• Applications

•

Maintenance

e)

RADIO

CORPORATION

0'

AMERICA

~

.'

~l:

ELECTRON

TUBE

OlVISION

HARRISON,

N.J.

~

ELECTRONIC

INSTRUMENTS

CAMDEN,

N.

J.

Safety

Precautions

The

metal

case of this instrument

is

connected

to

the

ground

of

the

internal circuit.

For

proper

opera-

tion,

the

ground

terminal of

the

instrument should

.always

be

connected

to

the

ground of

the

equipment

under

test.

The

WG-349A

Direct/Low-Capacitance

Probe

and

Cable

has a shield throughout its entire

length

which

is

connected

to

the

instrument

ground

and

case.

Care

should

be

exercised to avoid striking

the

cathode-ray

tube

or subjecting it to more

than

mod-

erate

pressure

in

handling.

Because

the

tube

contains

a high

vacuum,

implosion might result in injury

from flying glass.

An

important

point

to

remember

is

that

there is

always

danger

inherent

in testing electrical

equip-

ment

which

operates

at

hazardous voltages. There-

fore,

the

operator

should

thoroughly familiarize him-

self with

the

equipment

under

test before working

on it,

bearing

in

mind

that

high voltages

may

appear

at

unexpected

points in defective

equipme~t.

Addi-

tional

precautions

which

experience in

the

industry

has

shown

to

be

important

are listed below.

1.

It

is good

practice

to

remove power before

connecting

test

leads

to

high-voltage points.

If

this

is impractical,

be

especially careful to avoid acci-

dental

contact with

equipment

racks

and

other

ob-

jects which

can

provide a ground.

Working

with

one

hand

in your pocket

and

standing

on

a properly

insulated

Hoor

lessens the

danger

of shock.

2. Filter capacitors may store a

charge

large

enough

to

be

hazardous. Therefore,

discharge

filter

capacitors before

attaching

test

leads.

3.

Remember

that

leads with

broken

insulation

provide

the

additional

hazard

of high voltages

ap-

pearing

at

exposed points along

the

leads.

Check

test leads for frayed or broken insulation before

working

with

them.

4. To lessen

the

danger

of accidental shock,

disconnect test leads immediately

after

test

is

completed.

.5.

Remember

that

the

risk of severe shock

is

only

one of

the

possible hazards.

Even

a minor shock

can

place

the

operator

in'-hazard of

more

serious

risks such as a

bad

fall or

contact

with

a source

of

higher

voltage.

B.

The

experienced

operator

continuously

guards

against injury

and

does

not

work on

hazardous

cir-

cuits unless

another

person is available

to

assist

in

case of accident.

ITEMS

Supplied

with

WO-33A

Direct/Low-Capacitance

Probe

and

Cable

Type

No. WG-349A

1

BX4

1

BBK7A

1 BC4 2

12AT7

1 BBR8

Instruction Booklet

Available

on

Separate

Order

1 RCA

3AQPl

For

rf

applications from

500

Kc to 250 Mc:

Demodulator

Probe ........

Type

No. WG-350A

Devices

or

arrangements

shown

or

described

herein

may

use

patents

of

RCA

or

othet's.

Information

contained

herein

is

furnished

without

responsibility

by

RCA

for

its

use

and

without

prejudice

to

RCA's

patent

rights.

TMK

®.

Marco

Registrodo

• 2 •

WQ-3]AIB(2)

3-60

Printed

in

U.S.A.

Cathode-Ray Oscilloscope

Type

WO-33A

Contents

Safety

Precautions

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

Items

Supplied

with

WO-33A

Description

Specifications

Functions

of

Controls

and

Terminals.

Operation

Initial

Procedure

Vertical-Amplifier

Operation

Horizontal-Amplifier

Operation

Sweep-Oscillator

Operation

Use

of

WG-349A

Probe

Calibration

and

Voltage

Measurement

Applications.

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

Analyzing Composite Television Waveforms

Alignment

Schematic

Diagram

of

WO-33A

.......

General

Applications

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

Square-Wave

Testing of Audio Amplifiers

..

Phase-Shift Measurements

Frequency

Measurements ............................ .......

..

Industrial

Applications

...........................,

..

Engine-Pressure Analysis

Vibration Measurements

.

Maintenance.

General

Astigmatism Adjustment

Vertical Attenuator Alignment...............

Internal Calibrator Control Adjustment...

Repair

Service

Replacement

Parts

List.

Warranty

• 3 •

Page

:\'/0,

2

5

6

8

9

..11

..........

11

14

12-13

18

19

20

21

..... 21

21

...

21

22-2.3

23

Description

The

RCA

WO-33A

is a 3-inch oscilloscope de-

signed for "on-location"

and

service-shop use in

servicing color

and

black-and-white television re-

ceivers, Hi-Fi

equipment,

PA

and

sound reenforcing

systems,broadcast

station

and

remote equipment,

communications

and

industrial electronic equipment.

A novel feature of

the

WO-33A is

the

Vertical

Input

Attenuator

which

automatically switches

the

amplifier from

Wide

Band

to Narrow Band

when

in

the

three

highest

gain positions.

Another

important

feature of

the

WO-33A

is

the

exceptionally

high

gain in its vertical amplifier.

There

is enough sensitivity

to

provide a useful dis-

play of signals from low-level microphones, phono-

pickups

and

other

weak

signals found in radio/TV

receivers, audio amplifiers, etc.

A voltage-calibrated, frequency-compensated ver-

tical-input attenuator,

an

internal calibrating-voltage

source,

and

a

graph

screen scaled directly in volts

make

it

possible

to

use

the

WO-33A as a visual

voltmeter.

The

unique

system of calibrating the

graph

screen provides for scaling voltages directly

from

the

screen.

The

measurement

procedure

is

very

similar

to

that

employed

with

a vacuum-tube volt-

meter. A calibrating voltage

is

automatically applied

to

the vertical amplifier

when

the

bandwidth

control

is

set

to

the

calibration position. This switch also dis-

connects internally

the

input

and

attenuator

circuits,

making

it

unnecessary

to

remove leads

and

probes

from

the

external circuit

under

test. These unique

facilities make voltage calibration

and

measurement

a simple, almost

automatic

procedure.

The

sweep-frequency control

is

continuously

adjustable from 15 cps

to

75

Kc.

The

sweep oscil-

lator has excellent stability

at

high sweep rates, a

fast retrace,

and

adequate

linearity throughout its

frequency range.

The

over-all frequency range of

the

oscillator

is

divided

into four basic ranges; a

vernier adjustment,

which

overlaps

the

basic sweep

ranges, provides exact

adjustment

of

the

sweep fre-

quency.

The

amount

of sync signal

fed

to

the

sweep

oscillator may

be

adjusted

by

means of a front-panel

• 4 •

control. Sweep synchronization is exceptionally

stable throughout

the

sweep range

of

the oscillator.

A

phase

control is provided for varying

the

phase

of the internal sweep voltage

when

the

"LINE"

position of

the

H/SWEEP

SEL

cOlltrol

is

used, en-

abling

the

WO-33A to

be

phased

with

an

external

line-frequency sweep oscillator.

To

facilitate its use,

the

WO-33A is

equipped

with

a specially designed single-unit

probe

and

input

cable. This accessory,

the

WG-349A

DirectiLow-

Capacitance Probe

and

Cable, is provided

with

a

blue

input

lead

and

a yellow input lead.

When

the

blue

input

is used,

the

test signal

is

fed directly

to

the

vertical-input terminal.

When

the

yellow

input

is

used, a special high-impedance circuit

in

the

probe

is

connected in series with

the

test point

and

the

'scope. This high-impedance circuit presents

an

over-

all

input

resistance of 10 megohms

and

an

input

capacitance of approximately 10

ppf

to

the

test

cir-

cuit. This feature reduces circuit-loading effects

and

permits use

in

circuits which would not function

properly

if

loaded

down

by a conventional oscillo-

scope.

The

WO-33A

can

be

used to trouble-shoot

and

signal

trace

all sections of

both

black-and-white

and

color-TV receivers. The voltage-calibrating facil-

ities,

wide

band-pass,

and

high-impedance

input

characteristics make possible observations

and

meas-

urements of color-burst signals

and

othe'; critical,

,.

high-frequency waveshapes in circuits

which

are

sensitive to loading effects.

The

size

and

weight

of the WO-33A make

it

an

especially portable instrument, useful

in

such

appli-

cations as industrial maintenance

and

trouble-shoot-

ing, general waveform analysis, adjustment of

radio

receivers

and

transmitters, square-wave

and

general

testing of audio equipment, peak-to-peak voltage

measurements,

and

observation of

vacuum-tube

characteristics.

The

WO-33A is a versatile

and

re-

liable instrument, well suited to applications

which

require a

dependable

oscilloscope.

Specifications

NOTE:

Performance

figures

are

for

a line

voltage

of 117

volts,

60

cps.

Frequency

Response:

Electrical

Vertical Amplifier:

Wide-Band Positions (5.5 cps to 5.5

Mc)

..................................................... flat within - 3

db

High-Sensitivity Positions:

20

cps

to

150

Kc

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

3 cps to 1.5 Mc .....................................................

Horizontal Amplifier (3.5 cps to 350 Kc)

Deflection

Sensitivity:

Vertical Amplifier:

At V

INPUT

connector .......................................

With WG-349A Blue Lead

With WG-349A Yellow

Lead

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

(Wide-Band)

Positions

rms

p-p

0.10 0.3

1.0 3.0

...... flat within - 3

db

flat within - 6 db

.... flat within - 6 db

(High-Sensitivity)

Positions

rms

p-p

.003 0.01 volt/in

.03 0.1 volt/in

Horizontal Amplifier

(at

H

INPUT

terminal)

Rise

Time

(Vertical Amplifier):

.......................................................................................... 0.9

rn1S

volt/in

5.5-Me Positions 0.1 psec

Input

Resistance

and

Capacitance:

Vertical Amplifier:

At

V

INPUT

connector ......................... ................. ............... ...................... 1 megohm shunted by approx. 50

f.Lpf

With

WG-349A Blue Lead ...................... ............... ..............

...

...... 1 megohm shunted by apf)fox. 90

f.Lf.L

f

\Vith \VG-349A Yellow

Lead

.................... .................................. 10 megohms shunted by

ap~rox.

10

pf.Lf

Horizontal Amplifier

(at

H

INPUT

terminal) .................................................... ......

io

megohms

EXT

SYNC

Input

Terminal........................ ..................................................................... 250 K to 55 K

Sweep

Oscillator:

Frequency Range (continuously adjustable)

Sync ....................................

Sync

Range.

Maximum

AC

Input

Voltage

(at

Lo-Cap

Probe):

(In

presence of 400 volts

dc)

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

Phase-Control

Range

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

Power

Requirements:

Voltage ....

Average Power Consumption .....................................

1-6BR8

1-6BK7A

Tube

Complement

2-12AT7

Height

Width

1-6X4

Mechanical

8

31f1

14

61111

12

• 5 •

Length

Weight

15 cps to 75

Kc

........................ External; ± Internal

...

To

4.5 Mc

..... 600 p-p volts

oto 160 degrees

105-125 volts, 50-60 cps

............ 50 watts

1-6C4

1-3AQPl

.......

lOW'

14 lbs

Functions

of

Controls and Terminals

o 0 0 0

E;)a=JE;)

00

OFF-INTENSITY -Applies

power

to

the

instrument

and

in-

creases intensity of

the

trace

on

the

screen of

the

cathode-ray

tube

when

control

is

turned

clockwise

from

"OFF"

position.

FOCUS -Adjusts

the

sharpness

of

the

trace. Normally requires

adjustment

when

setting

of

the

INTENSITY

control is

changed.

000

0

o 0 0 0 v

POS

-Adjusts vertical posi-

tion of trace.

H

POS

-Adjusts horizontal po-

sition of trace. o

000

• 6 •

V-CAL -Adjusts sensitivity, or

calibrates vertical amplifier to cor-

respond with positions on V

RANGE switch.

°n°

O~O

000

0

E;)c=~

00

V RANGE -

In

"CAL"

position,

disconnects vertical amplifier from

input

connector,

and

supplies a

calibrating voltage which should

be

adjusted

with "V-CAL" control

to

full-screen deflection. Adjusts over-

all sensitivity of vertical amplifier

in

"3-to-l"

steps. Automatically

changes

bandwidth

of vertical amplifier when going

from ".2" to ".6" positions.

V INPUT -

Feeds

the

input sig-

nal to

the

vertical amplifier through

the

attenuator

circuits.

:0:

000

°

&c=

~

'lac

00

SYNC -Selects the source of

the

synchronizing signal.

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RCA

WO-33A Cathode-Ray Oscilloscope iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

:0:

o~/=o~o

~c

00

GND -Connected directly to case

and

chassis.

H/SWEEP

SEL

-Selects

the

frequency

range

of

the

sweep

os-

cillator.

Used

in conjunction with

the

SWEEP

VERNIER

control.

Also switches

the

Horizontal Amp-

Mer

to

"H

INPUT"

or to a sine-

wave sweep voltage of power-line

frequency.

0(jJ}0

o 0

000

00

SYNC/PHASE -Controls

the

amplitude

of

the

synchronizing

voltage applied to

the

grid of

the

sweep oscillator; should

be

adjusted

to minimum setting necessary to

lock

pattern

in a stationary position.

Works zero-center for internal

sync. Adjusts external sync by reg-

ular clockwise rotation. Also controls phase of

the

sinusoidal

sweep

voltage

when

the

H/SWEEP

SEL

switch is in

the

"LINE"

position.

• 7 •

:0:

EXT

SYNC/H

INPUT

-An

external synchronizing signal for

the

sweep

oscillator should

be

con-

nected

between

this terminal

and

the

ground

terminal.

The

"SYNC"

switch should

be

set to "EXT". An

external signal for the horizontal

amplifier should also be connected

between this terminal

and

the

ground terminal

and

the

H/SWEEP

SEL

control set to

"H

IN". A positive-

going signal will cause

the

spot to deflect to

the

right; a negative-going signal will cause

the

spot to

deflect to

the

left.

SWEEP

VERNIER -Provides

continuous control of

the

oscillator

sweep frequency over

the

range

selected by

the

SWEEP

controL

Also provides overlap

of

the

SWEEP

control positions.

0QO

o 0

000

0Q

o 0

000

H GAIN -Adjusts

the

gain of

the

horizontal amplifier

and

varies

the

width

of

the

horizontal trace.

Does not provide

enough

control

to

reduce

trace length to zero.

Operation

To

become familiar with

the

operation of

the

WO-33A Oscilloscope, it

is

recommended

that

the

operator follow

the

procedure outlined below in

the

order

given.

The

section "Function of Controls

and

Terminals" on pages 6

and

7 of

the

block diagram

on

page

20 will also

be

helpful.

Initial

Procedure

1.

Connect

the

power

cord

at

the

rear

of

the

instrument to

an

ac

outlet supplying 105-125 volts

at

50-60 cps.

2.

Turn

the

INTENSITY

control clockwise from

the

"OFF"

position

and

wait a

few

seconds for

the

instrument to

warm

up.

3. Rotate

the

INTENSITY

control farther clock-

wise until, either a spot or a horizontal line appears

on

the

screen.

The

spot or line should increase in

brilliance as

the

control

is

turned

clockwise.

NQTE:

Do

not allow a small spot of high brilliance to remain

stationary on

the

screen for

an

appreciable length of

time because discoloratiol'l or

burning

of

the

screen

may

result.

4. Adjust

the

FOCUS

control for

an

image of

maximum sharpness.

5.

Turn

the

H/SWEEP

SEL

control to

the

"H-

IN"

position.

In

this position,

without

an

external

signal

being

applied

to

the

H-INPUT

terminals, no

sweep

voltage,

appears

at

the

horizontal-deflecting

electrodes of

the

cathode-ray

tube

and,

therefore,

only a spot will appea'r on

the

screen,

6. Position

the

spot in

the

center

of

the

screen

by

adjusting

the

V POS

and

H POS controls.

Vertical-Amplifier

Operation

1. Connect

the

WG-349A

probe

connector to

the

V

INPUT

connector, Set

the

V

RANGE

control

to

"CAL".

The

screen should

now

display a vertical

trace, indicating

that

a signal has

been

applied to

the

vertical-deflecting electrodes of

the

cathode-ray

tube.

2.

Change

the

height

of

the

vertical trace

by

rotating

the

V

CAL

control.

3.

Set

the

H/SWEEP

SEL

to

the

dot

between

15

and

150.

• 8 •

4. Lock in as described

under

"Sweep Oscillator

Operation"

.

Horizontal-Amplifier

Operation

1.

Apply an ac signal of from 1 to 3 volts to

the

EXT

SYNC/H

INPUT

terminal. An audio-frequency

generator

or

a 60-cps line signal

may

be

used

as

the

source. Set

the

HJSWEEP

SEL

to

"H

IN", set

the V RANGE control

to

60,

and

set

the

H GAIN

control fully clockwise. A horizontal line will appear

on

the

screen, indicating

that

an

external signal has

been applied to

the

horizontal-deflecting electrodes

of

the

cathode-ray

tube.

2. Disconnect

the

lead

from

the

voltage source.

The

horizontal line will

be

replaced

by

a spot.

3.

Tum

the

H/SWEEP

SEL

to

the

"LINE"

position. A horizontal line should appear. NOTE:

When

the

H/SWEEP

SEL

switch

is

set

to the

"LINE"

position,

part

of

the

power-line signal

is

fed internally to

the

horizontal amplifier, providing a

sinusoidal horizontal-deflection voltage of power-line

frequency.

The

SYNC/PHASE

control can

be

nsed

to adjust

the

phase

of

the

internal sinusoidal sweep.

4.

Turn

the

H/SWEEP

SEL

control

to

any of

the sweep positions.

The

sawtooth

output

from

the

sweep oscillator is

applied

internally to the horizontal

amplifier

and

a linear horizontal trace appears on

the screen.

Sweep-Oscillator

Operation

1.

Adjust

the

H/SWEEP

SEL

and

the

SWEEP

VERNIER control to give a sweep of approximately

power-line frequency. Connect

the

ground lead

from the WG-349A

to

the

ground side

of

an

ac-voltage source. An audio-frequency generator or

a power-line signal can

be

used as a source. With

the cable connector of

the

WG-349A

attached

to the

V

INPUT

connector of

the

WO-33A, connect the

blue lead to the

other

side of

the

low-voltage source.

Adjust

the

SWEEP

VERNIER

control for a single

cycle on

the

oscilloscope screen. Rotate

the

SYNC/

PHASE control

and

note

that

it

should

be

adjusted

to a minimum position neeessary to lock

pattern

in

a stationary position.

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

..

RCA WO-33A Cathode-Ray Oscilloscope

2.

With

a single

pattern

on

the

scr~n,

notice

whether

the

pattern

drifts across

the

face of

the

tube.

Horizontal

drift

indicates

that

the

SYNC/PHASE

control should

be

rotated toward its clockwise or

counterclockwise limits or

that

the

SWEEP

VERN-

IER

control

should

be

adjusted until

the

waveform

is locked in.

3.

Connect

the

WG-349A connector to an external

signal of a different frequency.

4.

Set

the

H/SWEEP

SEL

control to «H

IN"

and

adjust

the

H/SWEEP

and

SWEEP

VERNIER con-

trols to produce a suitable sweep frequency. Apply

a synchronizing voltage from the external signal to

the

EXT

SYNC terminal. Set

the

SYNC switch to

"EXT".' Adjust

the

SYNC/PHASE control until

the

pattern locks

in

on

the

oscilloscope screen.

Figure

1.

WG-349A

direet/low-capacitance

probe

and

cable

supplied

with

WO-llA

Use

of

the

WG-349A

Direct/Low-Capacitance

Probe

The WG-349A Direct/Low-Capacitance Probe and

Cable is

designed

especially for use with

the

WO-

33A Oscilloscope. This single-unit probe

is

equipped

with two clips

from

the

probe

housing which permits

using

the

probe

for direct measurements or for

connecting a built-in high-impedance network in

series

with

the

test

point

and

the

probe cable. When

the

yellow lead is used,

the

input capacitance of

the

cable

and

scope is reduced to 10

/L/Lf

and

the,input

resistance

is

raised to 10 megohms. These high-im-

peda'1ce characteristics permit use of

the

WO-33A

in

high-impedance circuits, such as those found in

TV sync-separator

and

video-amplifier stages, which

would

not

operate

properly if loaded down

by

a

conventional

scope

probe

and

cable.

Whenever

the

probe

is

used in its low-capacitance

position, however,

the

signal

is

attenuated by a

factor of ten. Therefore,

when

voltage measurements

• 9 •

Figure

2.

WO·llA

graph

screen

with

voltage

scales

are made,

the

indicated voltage should

be

multiplied

by 10.

Calibration

and

Voltage

Measurement

Special facilities

on

the

WO-33A provide for

simple

and

quick voltage calibration of

the

vertical

amplifier

and

the'

cathode-ray

tube

screen.

When

the

oscilloscope has

been

calibrated as indicated be-

low,

the

graph-screen scales can

be

used to measure

the

deflection amplitude of a displayed waveshape

directly

in

volts.

The

green-graph screen has two vertical scales, as

shown in' Figure 2.

The

scale used depends

upon

the setting

of

the

V RANGE control.

Calibration

is

accomplished as follows:

1. Set

the

V RANGE control to "CAL".

2. Adjust

the

V POS

and

V

CAL

controls for

enough vertical deflection to fill

the

graph

screen

between

the

two horizontal lines indicated

by

the

"CAL" arrow on the side of

the

graph screen.

The

WO-33A

is

now calibrated.

When

the

V RANGE control

is

set to "CAL",

the

probe, cable,

and

input attenuator circuits in

the

scope are automatically disconnected from

the

verti-

cal amplifier

and

an internal calibrating voltage is

applied.

The

H/SWEEP

SEL

control

may

be

set to

any position during calibration. A straight vertical

line

is

obtained by setting this control to

"H

IN",

A sinusoidal waveshape

is

obtained

when

the

HI

SWEEP

SEL

is

set to any other position.

oOiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

RCA WO-33A Cathode-Ray Oscilloscope

Calibration

will

hold

for

both

the

wide

band

and

narrow

bandwidth

positions. After calibration,

an

input

signal

may

be

read

directly in peak-to-peak

volts

by

measuring

the

vertical deflection against

the

correct

graph-screen

scale.

Example:

It

is desired

to

simultaneously display

and

measure

the

peak-to-peak voltage

amplitude

of

the

horizontal

driving

pulse

at

the

grid

of

the

horizontal-deflection-output stage in a

TV

receiver.

Procedure

is as follows:

1. Set

the

bandwidth

control to

"CAL"

and

set

the

H/SWEEP

SEL

to

"H

IN".

2.

Adjust

the

V

CAL

control for exactly full

scale vertical deflection as

measured

on

the

graph

screen.

Adjust

the

V POS control so

that

the

bottom

of

the

trace

rests

on

the

base-scale line

and

the

top

of

the

trace

rests

on

the

upper

horizontal line.

3.

The

WO-33A

is

now

calibrated.

4.

Connect

the

ground

lead

from

the

WG-349A

to

the

TV

chassis.

Connect

the

blue

probe

clip to

the

appropriate

tube-socket pin.

5.

Set

the

V

RANGE

control to a position which

gives

the

desired on-screen deflection of

the

wave-

shape.

6. Lock in

the

waveshape

as

described

under

"Sweep Oscillator

Operation".

7. Adjust

the

V

POS

control to position

the

bottom

of

the

trace

on

the

graph-screen

base

line.

8.

Read

the

peak-to-peak

voltage

amplitude

of

the

waveshape

from

the

appropriate

scale on

the

graph-

screen.

The

peak-to-peak

voltage

is

read

from

the

scale

point

opposite

the

top

of

the

waveshape.

NOTE:

If

the

WG-349A

is

used

in its low-capaci-

tance position,

an

attenuation

factor of

10

is

intro-

duced

and

it

will, therefore,

be

necessary

to

multiply

the voltage

reading

by

10 to

obtain

the

correct

peak-to-peak voltage

amplitude.

• 10 •

Applications

Successful servICIng

and

maintenance

of black-

and-white

and

color-television receivers requires

special techniques,

not

usually

employed

in

the

serv-

icing of

other

electronic

equipment.

The

general

complexity

and

variety of circuits

used

in

modem

television receivers requires a

great

deal

of

knowl-

edge

on

the

part

of

the

service technician

and

de-

mands

that

test

equipment

be

used

properly.

The

oscilloscope is

of

especial importance in

the

servicing of color receivers. A good television-service

oscilloscope,

such

as

the

RCA WO-33A, may

be

u5ed in signal

tracing

in every section

of

the

receiver;

the

'scope

may

also

be

used

for

making

peak-to-peak

voltage measurements in such

important

sections of

the receiver as

the

sync

and

deflection circuits

and

in the video, chrominance,

and

luminance sections

of color-TV receivers.

In

alignment work, where

video, chrominance,

and

luminance circuit adjust-

ments must

be

made

to

produce

the

desired wave-

shape,

the

oscilloscope is indispensable.

The

WO-33A

may

be

used

in

all

these

applications.

Signal-tracing

means

tracing

the

television signal

through various sections of

the

television receiver

to

determine

how

circuits

are

functioning in terms

of

the

shape

and

voltage value of

the

waveform. As

the signal passes from one stage

to

another

in

the

receiver,

the

shape

of

the

waveform

may

be altered,

Fi9ure

3.

Horizontal-sync

pulse

in

composite

signal

Fi9ure

4.

Vertical-sync

pulse

In

composite

signal

•

11

•

and

the

height,

or

voltage

amplitude

of

the

wave-

form may be changed.

Whenever

possible,

the

WG-349A probe should

be

used

in

the

"LOW

CAP" position for signal tracing

the

video amplifier

and

chrominance circuits because of

the

low

input

capacitance and

consequent

negligible

loading

of

the

circuit

under

test.

When

the

WO-33A is

calibrated

as described

under

"Operation",

it

is possible to

simultaneously

read

the

voltage value

and

observe

the

shape

of

the

waveform.

The

process

of

signal

tracing

is

thus

speeded

up

and

it

is

possible

to

as-

certain a circuit condition quickly.

NOTE:

The

applications described

here

apply

both

to

color

and

to black-and-white receivers.

Analyzing

C~mposite

Television

Waveforms

Probably

the

most important waveform

encounter-

ed

in television service work

is

the

composite video

waveform consisting of

the

video signal,

the

blanking

pedestals,

and

the

sync pulses.

Photographs

of

the

composite video signal

are

shown in

Figures

3

and

4.

The

photographs

are

oscilloscope traces,

and

show

what

the composite video signal looks like as

it

pro-

ceeds through

the

video amplifier of a television

receiver.

The

television service technician should

devote

some time to

the

study

of such waveforms

by

setting

up

a television receiver known to

be

in

goodoper-

ating

condition

and

noting

the

waveforms

on

the

WO-33A

at

various points in

the

video amplifier.

Traces similar to those shown in Figures 3

and

4

may

be

obtained

on

the

WO-33A as follows:

(Continued on page 14)

NORMAL

fl,

..

SYNC

PULSE

J •

SYNC

PULSE

~

COMPRESSION

CAUSED

BY

JJ

LIMITING

'it'

"WHITE"

'l

SATURATION

CAUSED

BY

LIMITING

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Figure 5. Sync-pulse

compression

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NOTES

ALL

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IN

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UNLESS

OTHERWISE SPECIFIED.

ALL

RESISTQRS

IN

OHMS.

ALL

VQLTAGES POSIT!

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AND

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POSITIQN

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NO:S

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HAVE

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DISC

CAPACITORS

BETWEEN

THE

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AND

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GROUND

V

RANGE

FULL 'SCALE VOLTS (p-p)

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RANGE

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• Schematic Dia9ram

ef

WO-33A and

WO.l3A(K)

•

TRAD(-MARK

"VOLTOHMYST"

REG.

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PAT.

OFF.

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RCA W0-33A Cathode-Ray Oscilloscope

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

NORMAL

CIRCUIT

HORIZONTAL

OVERALL

FREQUENCY

EFFECT

ON

HORIZONTAL

FAULT

PULSE

RESPONSE OF

PICTURE

PULSE

DISTORTION

RECEIVER

J\

V1

NORMAL

PICTURE

CIRCUIT

~

NORMAL

r-

1\

LOSS

OF

HIGH

A.

~

LOSS

OF

FREQUENCIES

--.I

PICTURE

DETAIL

I--

EXCESSIVE

J)

V

FINE

VERTICAL

HIGH

-FREQUENCY

BLACK

& WHITE

RESPONSE,

STRIATIONS

FQL-

NON-LINEAR

LOWI

NG

A SHARP

PHASE

SHIFT

--l

"'-

CHANGE

IN

PIC-

TURE

SHADING

LOSS

OF

LOW

CHANGE

IN

SHA-

FREQUENCIES

1\

V 1

DING

OF

LARGE

(IN

THE

RANGE

PICTURE

AREAS;

ABOVE

15

OR

-

I-"'-

SMEARED

PIC-

20

KC)

TURE.

PICTURE

SOUND

CARRIER

Figure

6.

Sync-pulse

distortion

(Continued

from

page 11)

1.

Tune

the

television receiver to a television

signal.

2. Rotate

the

INTENSITY

control on

the

WO-33A

clockwise.

Set

the

SYNC control

to

"INT". Set

the

INTENSITY

and

FOCUS

controls for

the

desiredof

brightness

and

best

focus.

3.

Connect

the

WG-349A

probe

and

cable con-

nector to

the

V

INPUT

connector. Connect

the

ground

lead

to

the

receiver chassis. Connect

the

yellow

probe

clip to

the

grid terminal of the picture

tube

socket.

It

is

not

necessary

that

the

picture

tube

be

connected

for this test.

4. Set

the

V

RANGE

switch

and

the

V CAL

control for a

pattern

of convenient height.

5.

To

obtain

the

horizontal-sync pulse on the WO-

33A screen, set

the

H/SWEEP

SEL

control to

the

1500 • 15 Kc position. Adjust

the

SYNC/PHASE

control, if necessary, to

obtain

lock-in on

the

sync

pulse,

and

adjust

the

SWEEP

VERNIER

control

so

that

two

complete

waveforms

appear

on the

screen. To obtain

the

vertical-sync pulse, set the

HI

SWEEP

SEL

to

the

15

• 150 position. Readjust the

SWEEP

VERNIER

for two complete waveforms.

The

pulses should resemble those

shown

in

Figures

3

and

4.

Alignment

The

process of television-receiver alignment

probably requires a greater

amount

of skill

and

understanding on

the

part

of

the

service technician

than

does any

other

service function. Before

under-

taking alignment,

it

is

important

that

the

technician

recognize

the

symptoms of a misaligned receiver.

The

order in which various sections of the tele-

vision receiver

are

aligned may differ

between

split-

channel sound

and

intercarrier types. Different re-

ceivers of one system may also differ in

the

order

of alignment.

In

all cases, however,

the

alignment

order given

by

the

manufacturer in his service notes

should

be

followed.

For

these reasons, it

is

not feasible to present a

general alignment procedure applicable to all re-

ceivers. Some general precautions

and

suggestions

for using

the

WO-33A Oscilloscope, however,

are

provided below to aid

the

television technician in

servicing a receiver.

• 14 •

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii RCA WO-33A Cathode-Ray Oscilloscope iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

Receiver alignment requires, in addition to

the

WO-33A, a sweep generator, a marker generator of

crystal accuracy,

and

a

vacuum-tube

voltmeter.

An

RCA

WR-59

or WR-69-series Sweep Generator, an

RCA WR-39, WR-99 or

WR-89

Calibrator,

and

an

RCA VoltOhmyst"', such as

the

WV-77, \VV-87,

WV-97,

or

WV-98 are recommended.

Tuner

Alignment

-

When

preparing

for

tuner

alignment,

the

manufacturer's recommendations

should

be

followed closely.

If

the

tuner

has test

points for connecting

equipment,

the

test

points

should

be

used.

The

oscilloscope test point is usually

connected internally to

the

mixer grid circuit

where

a

demodulated

signal is present.

The

output

cable of

the

sweep generator should

be

connected

to

the

antenna

input

connectors.

The

ground

lead

of

the

W

0-33A

should

be

clipped

directly

to

the

tuner

shield to minimize

hum

pickup

on

the

sweep

trace,

and

the

WG-349A blue clip

should

be

connected to

the

mixer grid -circuit test

point.

If

no

test point

is

provided,

the

WG-349A

may usually

be

connected to

the

grid circuit through

a 5,000

to

10,000-ohm composition resistor.

It

is

important

that

the

WG-349A

be

connected

directly to

the

proper test point or, if a series resistor

is

used,

that

the

lead

length

between

the

probe

clip

and

the

mixer grid circuit

be

kept

as short as

possible

to

prevent

hum

pickup

and

possible dis-

tortion of

the

tuner

curve

on

the

WO-33A.

Hum

pickup is evidenced

by

twisting of

the

base line

when

return-trace blanking is used on

the

sweep

generator. This precaution

is

necessary because of

the

high-gain level

at

which

the

WO-33A is operated

for

tuner

alignment.

The

INTENSITY

control should

be

turned

clock-

wise to

obtain

a trace of suitable brilliance.

The

vertical

gain

controls should

be

set for maximum or

near

maximum gain.

The

output

from

the

sweep

generator

and

marker calibrator should

be

set

at

a

low level to avoid over-loading

the

TV

receiver,

distortion of

the

sweep curve,

and

an

erroneous

picture

of alignment on

the

oscilloscope screen.

When

the

WO-33A

is

used

with

a sweep generator,

it is

important

that

the

two instruments

be

adjusted

so

that

blanking is correct

and

the

sweep of both

instruments

is

in phase.

If

the

phase

adjustment

is

not

properly

set before starting alignment,

the

sweep

0Trade Mark "VoltOlunyst" Reg.

U.

S.

Pat.

Off.

Fi9ure 7. Double

rf-response

curve

caused

by

improper

settinq

of

phasin9

control.

No

blanking used

Figure 8.

Sharp'

cutoff

of

response

curve

and

misplaced

base

line with blanking

indicate

improper

settin9

of phasin9

control

Figure

9.

Typical

rf-response

curve

curve on

the

oscilloscope

may

be

prematurely

cut

off or

the

curve

may

appear

as a double or

"minor"

image.

These

effects, shown in Figures 7 and 8,

are

sometimes misinterpreted

as

being caused by mal-

functioning of test

equipment

although they

may

often

be

traced

to improper

tuner

alignment.

The

sweep generator may use either a sinusoidal

or sawtooth sweep' of line frequency.

If

a sinu-

soidal line-frequency sweep

is

used,

the

WO-33A

may

be

driven

internally

by

setting

the

H/SWEEP

SEL control to

"LINE".

If

a sawtooth sweep

is

used,

the sweep generator deflection signal may pe fed

to

the

H

INPUT

terminal of

the

\i\10-33A.

The

H/SWEEP

SEL

should

be

set to

"H

IN". An internal

sawtooth sweep may also

be

obtained by setting

the

H/SWEEP

SEL

to

the

15 • 150 position.

•

15

•

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RCA WO-33A Cathode-Ray Oscilloscope

;;;;;;;;;iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

If

no

blanking

is

used,

the

SYNC/PHASE control

should

be

adjusted until

the

two response curves

coincide on the oscilloscope screen.

If

blanking

is

used, the SYNC/PHASE control should be adjusted

until

the

base line

on

the

WO-33A screen extends

the full width of the curve trace. An extremely sharp

drop-off point on

the

response curve, which gives a

"chopped-off" appearance to

the

trace short of the

end

of its sweep range, also indicates improper

phasing.

When

a marker is superimposed on the

response curve, improper phasing will cause two

markers to appear

on

the

curve.

The

SYNC/PHASE

control should be adjusted to obtain

the

appearance

of a single trace having only one marker.

The

setting

of the SYNC/PHASE control is also important dur-

ing sweep alignment of

other

sections of the receiver.

Serious misalignment of

the

tuner

or considerable

difficulty or failure

in

alignment may

be

caused by

an unsuspected defective component.

If

proper

alignment procedure fails

to

produce correct tuner

curves,

the

technician should check individual com-

ponents in the rf unit.

Picture-IF

Alignment

-

To

obtain

an

over-all

picture-if response curve,

the

blue

clip of

the

WG-

349A probe should

be

connected across either the

second detector load resistor or to

the

grid of the

first video stage; test points which

can

provide a

demodulated signal to

the

oscilloscope.

The

ground

lead should be connected to

the

chassis. Because of

the additional amplification in this section of

the

receiver,

the

oscilloscope gain should

be

considerably

reduced,

but

not to.

the

point

where

it

is

necessary

to increase sweep-generator output.

Depending upon manufacturer's recommendations,

it may

be

necessary to adjust

the

agc

bias level, either

through temporary wiring changes or by providing

fixed battery bias.

The

service-notes should

be

fol-

lowed closely because alignment procedure may

involve considerable detail.

Trap

alignment is some-

times difficult because

the

marker disappears in the

trap notch. This may often

be

overcome by magnify-

ing

the

trap

section of

the

trace with the V CAL

and

H GAIN controls.

Adjustment of

the

SYNC/PHASE control

is

also

important when aligning

the

i-f sections of the re-

ceiver.

The

precautions

and

recommendations de-

scribed

under

the section

on

tuner

alignment, above,

should

be

observed here. Controls on the WO-33A

should

be

set the same

as

for tuner alignment ex-

cept

that

less vertical gain will be required.

For observation of the response of individual

stages in

the

picture-if amplifier,

the

WG-350A

Demodulator Probeo should

be

used. This

is

a high-

frequency rectifying-type probe.

It

is

important

that

this probe

be

used properly

and

in accordance with

service-note recommendations to prevent distortion

of

the response curve and an erroneous picture of

alignment.

The WG-350A, which connects to

the

V

INPUT

of the WO-33A,

is

equipped with a short

ground

lead

and

clip. For alignment work,

the

ground clip

of the probe should always

be

connected to

ground

near

the

test point being used for

the

WG-350A.

When the WG-350A

is

used to check individual

stages, it should be connected on the

output

side of

the stage being adjusted.

For

example, if

the

align-

ment of a coupling transformer is to

be

checked,

the

probe should

be

connected to the

plate

of

the

tube

which

has

its grid coupled to the transformer.

The

tube thus acts as a buffer between

the

high-imped-

ance grid circuit

and

the probe.

For general signal-tracing work, the probe may

be

moved from grid to grid throughout

the

i-f amplifier.

Figure 10. (A)

Ratio-detector

curve

and

(8)

sound-if

curve

Sound-IF

and

Detector

Alignment

-Most

television receivers use either a discriminator or ratio

detector.

For

either type, the WG-349A probe clip

should

be

connected to the output

of

the

sound

detector. For detector alignment,

the

sweep

and

marker generators should be connected to the re-

ceiver

as

described in the service notes. An S-shaped

curve, similar to that shown in Figure lOA, should

be

obtained on

the

oscilloscope screen.

The

setting of

controls on

the

WO-33A should remain the same as

before. A typical sound-if curve

is

shown in

Figure

°Available on separate order.

• 16 •

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RCA WO-33A Cathode-Ray Oscilloscope

;;;;;;;;;iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

INCORRECT

CORRECT

Figure 11. Horizontal-oscillator

waveforms

lOB.

To

obtain

the

sound-if response curve, the

probe should

be

connected to either

the

grid-return

of

the

limiter stage or to the grid-return of the last

sound-if stage.

The

SYNC/PHASE control should be

set no farther clockwise than necessary to lock in

the waveshape.

Horizontal-Oscillator

Adjustment

-

The

WO-33A is well suited to adjustment of

the

hori-

zontaloscillator

and

may be used

as

follows:

Set

the

WSWEEP

SEL control to

the

1500 •

15 Kc position.

HORIZ.

HOLD

CONTROL

Adjust the SYNC/PHASE control to give stable

lock-in of the waveshape, if necessary.

With the ground lead connected to

the

receiver

chassis, connect

the

yellow clip of

the

WG-349A

to the output of

the

horizontal oscillator, as described

in the service notes. Connection to a typical hori-

zontal-oscillator circuit is shown in

Figure

12. Because

the horizontal oscillator

is

a high-impedance circuit,

the low-capacitance clip should always

be

used to

reduce capacitance-resistance loading effects. Usually

it

is

necessary to adjust

the

oscillator for suitable

output waveshape. Typical horizontal-oscillator

waveshapes which

can

be

observed on

the

WO-33A

are shown in

Figure

13.

Sync-Separator·

Waveshape

-To observe

waveshapes in

the

sync-separator stage, the low-

cap yellow clip should

be

used. Controls of the

WO-33A should

be

set the same as for observation

of the horizontal waveform.

The

probe clip should

be connected to

the

plate of the sync separator or

to the plate or grid of

the

sync amplifier.

WG

-349A

USE

LOW'CAP

YELLOW

CLIP

HORIZ.OSC.

TRANS.

S-----I

.--------<~

tt

\

FROM

....I-----k

I

SYNC.

AMP. TO

HORIZ.

H0RI

Z.

..-----<>---H--+---------40

1.....,...,4-+.4~.....,...)("")(""'IrI:

........

___4_

0UT

PUT

LOCKING

STAGE

RANGE

CONTROL II

Figure 12. Adiustment

of

horizontal oscillator

• 17 •

WO-33A

o

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii RCA WO-33A Cathode-Ray Oscilloscope

Figure 13. Color.TV signals

as

displayed

by

WO·33A. (A) Com.

posite

eolor·TV signal.

Color-burst

ean

be

seen

to

left

of

syne

pulse. (B)

Output

signal from RCA WR-61A Color-Bar

Generator

showing color-sync pulses

and

10

color-bar

pulses.

General Applications

Square-

Wave

Testing

of

Audio

Amplifiers

The

use of square waves for testing

the

charac-

teristics of audio equipment has distinct advantages

over other methods. A square-wave generator

and

the

WO-33A Oscilloscope,

when

set

up

as shown

in

Figure 14,

can

provide a quick

and

accurate means

of checking

an

amplifier

and

its adjustments.

In

this

test setup, it is possible

to

check simultaneously the

amplitude, phase,

and

frequency characteristics of

the

amplifier.

The

value of

the

load resistance used depends

upon

the

output

impedance of

the

amplifier.

It

is

important

that

the

correct value

be

used.

For

an

over-all check of amplifier response,

the

WO-33A

should

be

connected directly across

the

load re-

sistance, as shown.

It

is desirable to employ square waves of

at

least

two fundamental frequencies.

The

lowest funda-

mental frequency should

be

equal to approximately

ten times

the

low-frequency limit of the amplifier

being tested. A 100-cycle square wave should serve

to check response from a few cycles to over 1000.

If

a square wave having a fundamental frequency

of 2 Kc

is

used,

the

amplifier may be checked

through

the balance of

the

audible range.

The square-wave generator should be set to

the

proper frequency

and

connected to

the

regular

input

terminal of

the

amplifier.

The

WO-33A

may

be

connected temporarily directly across the generator

for a reference check of

the

waveform.

The

WO-

33A may

then

be

connected to various points

in

the

amplifier to determine how each stage

is

functioning.

The effect of various adjustments may be seen

on

the screen.

Care should

be

taken to prevent too large a signal

from

the

square-wave generator from overloading

the amplifier

and

causing distortion of the

square

wave.

Phase-Shift

Measurements

To measure

the

phase shift of an audio network,

apply a sine wave to the circuit

under

test

and

con-

nect

the

direct

probe

to

the

output

terminal of

the

network. This test signal should also be fed to

the

oscilloscope

through

the

H

INPUT

and

GND

terminals. Set

the

H/SWEEP

SEL

control to

the

"H

IN" position.

If

no phase shift exists, a sloping

straight line will appear. Phase shift is indicated as

an elliptical or circular trace.

The

method of calcu-

lating

the

degree of phase shift is shown graphically

in Figure 16.

SQUARE-

WAVE

GENERATOR

AUDIO

AMPLIFIER

LOAD

YELLOW

NOT

USED

WG-349A

FICJure

14.

Audio amplifier

test

setup

• 18 •

iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii RCA WO-33A Cathode-Ray Oscilloscope

/ /

NO

AMPLITUDE

DISTORTION

AMPLITUDE

DISTORTION

NO

PHASE

SHIFT

NO

PHASE

SHIFT

C 0

NO

AMPLITUDE

DISTORTION

AMPLITUDE

DISTORTION

PHASE

SHIFl

PHASE

SHIFT

Figure 15. Distortion

and

phase. shift

in

audio amplifier

Frequency

Measurements

Two methods may be used to determine fre-

quency.

In

one method, a sine wave of known

frequency is applied to the H

INPUT

terminal and

the

H/SWEEP

SEL

is

set to

"H

IN".

The

unknown

signal is fed to the V

INPUT

terminal.

The

re-

sulting

pattern,

or Lissajous figure, indicates the

ratio

between

the two frequencies. Typical Lissajous

figures

are

shown in Figure 17.

In

the

other method of frequency measurement,

the

H/SWEEP

SEL

should

be

set

at

"LINE"

to

provide a sweep of line frequency.

The

signal of

unknown frequency should be applied to the V

INPUT

terminal.

If

a stationary pattern

is

obtained

on the oscilloscope screen,

the

frequency of the input

signal

must

be

equal to, a submultiple of, or a

multiple of

the

line frequency.

..

19 •

r

A

SINE

cp

=

~

•

[ WHERE

cp

=PHASE ANGLE

0

Figure 16.

Measurement

of

phase

shift

UNKNOWN

FREQUENCY

ON

VERTICAL

ELECTRODES;

STANDARD

FREQUENCY

ON

HORIZONTAL

ELECTRODES

RATIO

OF

UNKNOWN

TO

STANDARD.

D

6:1

Figure 17. Llssalous

fiCJures

RCA WO-33A User manual

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