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INNSTRUCTION

MAN

UAL

Serial

Number

Tektronix,

Inc.

S.W.

Millikan

Way

@

P.

©.

Box

500

@

Beaverton,

Oregon

97005

@

Phone

644-0161

@

Cables:

Tektronix

070-0896-00

169

oa

D

a

or

3

ee

2

en.

oe

cs

i

—

_—

.

a

—

oo

a

Type

S-4

®

CONTENTS

Section

1

Specification

Section

2

Operating

Instructions

Section

3

Circuit

Description

Section

4

Maintenance

Section

5

Performance

Check/Calibration

Abbreviations

and

Symbols

Parts

Ordering

Information

Section

6

Electrical

Parts

List

Mechanical

Parts

List

Information

Section

7

Mechanical

Parts

List

Section

8

Diagrams

Mechanical

Parts

List

Illustrations

Accessories

Abbreviations

and

symbols

|used

in

this

manual

are

based

on

or

taken

directly

from

IEEE

Stand-

ard

260

‘Standard

Symbols

for

Units,’’

MIL-STD-

12B

and_other

standards

of

the

electronics

in-

dustry.

at

the

rear-ofthe-manuat

Cha

nge

information,|

if

any,

is

located

£

i

Type

S-4

oo

a

3

=

2

fal

g

at

&

r)

ee

|

:

oe

:

oe

ee

Lae

oe

ee

:

Type

5S-4

SECTION

I

TYPE

S-4

SPECIFICATION

Change

information,

if

any,

affecting

this

section

will

be

found

at

the

rear

of

the

manual.

General

Information

The

Type

S-4

Sampling

Head

is

an

input

signal

processing

unit

for

Tektronix

sampling

units

such

as

the

Type

352,

355,

and

386.

Input

characteristics

of

the

sampling

system

are

determined

by

the

Type

S-4.

The

Type

S-4

has

an

input

im-

pedance

of

500

and

a

risetime

of

25

ps

or

less.

The

Type

S-4

can

be

installed

directly

into

a

sampling

unit

or

used

remotely

(with

the

Type

3S2

or

Type

355)

on

an

optional

3

foot

or

6

foot

extender

cable.

When

used

with

a

Type

356

Sampling

Unit

the

Type

S-4

is

plugged

into

the

dual-input

extender

cable

supplied

with

the

Type

356.

A

portion

of

the

signal

delivered

to

the

sampling

head

input

is

coaxially

coupled

to

the

sampling

unit

for

use

as

an

internal

trigger

signal.

The

Type

382

allows

selection

of

the

trigger

pickoff

signal

from

the

Channel

A

or

Channel

B

sampling

head.

Type

385

and

356

Sampling

Units

permit

use

of

the

trigger

pickoff

signal

only

from

Channel

A.

Use

of

this

trigger pickoff

signal

is

dependent

upon

the

type

of

sampling

unit

and

sampling

sweep

unit

used

in

the

system.

See

the

instruction

manual

for

your

sampling

unit

and

sampling

sweep

unit

for

further

information.

Vertical

deflection

factor

of

the

sampling

system

is

label-

ed

at

the

top

of

the

Type

S-4

as

mVOLTS/DIV;

the

label

refers

to

the

sampling

unit

Units/Div

switch

of

the

corre-

sponding

channel.

Digital

Unit

Programming

Connections

The

Type

S-4

has

two

contacts

at

its

rear

connector

that

program

the

decimal

and

units-of-measure

lamps

of

a

Tek-

tronix

Type

6RI1A

or

Type

230

Digital

Unit.

These

connections

are

not

used

with

a

Type

382

Sampling

Unit.

When

using

a

Type

355

or

Type

386,

one

of

the

sampling

head

contacts

notifies

the

digital

readout

unit,

through

the

sampling

unit

digital

control

circuits,

that

the

Type

S-4

is

a

voltage

meas-

uring

head.

This

causes

the

Volts

lamp

of

the

digital

readout

unit

to

light.

The

other

sampling

head

contact

notifies

the

digital

readout

unit,

through

the

sampling

unit

digital

control

circuits,

that

the

Type

$-4

sensitivity

requires

no

decimal

shift

of

the

numbers

around

the

sampling

unit

Units/Div

switch.

ELECTRICAL

CHARACTERISTICS

Characteristics

The

following

characteristics

apply

over

an

ambient

tem-

perature

range

of

0°C

to

+50°C

and

after

a

five

minute

warmup

providing

the

instrument

was

calibrated

at

a

tem-

perature

between

+20°C

and

+30°C.

Characteristics

listed

below

apply

only

after

the

Type

S-4

has

been

properly

mated

to

the

sampling

unit

and

indicator

oscilloscope

and

after

these

units

have

been

given

sufficient

@

warmup

time.

To

determine

the

particular

system

warmup

requirements,

refer

to

the

related

amplifier

and

indicator

oscilloscope

instruction

manual.

A

procedure

for

mating

the

Type

S-4

to

the

sampling

unit

can

be

found

in

the

Operating

Instructions

section

of

this

manual

ELECTRICAL

CHARACTERISTICS

Performance

Requirement

50Q

within

5%

Characteristic

Input

Resistance

Response

to

Step

Signals

Risetime

(10%

to

25

ps

or

less

(Verify

using

step

9,

90%)

Section

5.)

Pulse

Flatness

Devi-

ation

(after

90%

point

on

display}

Ops

to

400

ps

—10%

to

+10%

with

a

total

of

20%

or

less.

(Verify

using

step

10,

Section

5).

0%

to

+10%

with

a

total

of

10%

or

less.

(Verify

using

step

10,

Sec-

tion

5).

—2%

to

+2%

with

a

total

of

4%

or

less.

(Verify

using

step

10,

Sec-

tion

5).

400

ps

to

25

ns

25

ns

or

more

Maximum

Operating

|

1V

P-P

Signal

Voltage

Safe

Overload

Signal

|

Not

to

exceed

+

or

—5V

(DC

Voltage

plus

AC

peak}

Adjustable

in

the

sampling

unit

to

unity

for

signals

up

to

500

mV

P-P;

when

the

loop

gain

is

adjusted

to

unity

with

positive

input

signals,

the

loop

gain

will

be

within

5%

of

unity

with

negative

input

sig-

nals

and

vice

versa.

Loop

Gain

Baseline

Shift

(with

10

mV

or

less,

30Hz

to

50kHz

change

in

repetition

rate)

5mV

or

fess,

measured

tangen-

tially

Displayed

Noise

ENVIRONMENTAL

CHARACTERISTICS

Storage

Operating

Temperature—As

stated

above

Electrical

Character-

istics

table

Temperature—

—40°C

to

+65°C

Altitude—To

50,000

feet

Altitude—To

15,000

feet

1-1

Specification—Type

5-4

MECHANICAL

CHARACTERISTICS

Dimensions—

Height

=

2

inches

Width

=

1%,

inches

Length

=

4%,

inches

Construction—

Epoxy

laminated

circuit

boards.

Aluminum

Accessories—

wrap

around

cabinet

with

aluminum

casting

at

front

and

rear.

Anodized aluminum

front

panel.

An

illustrated

list

of

the

accessories

supplied

with

the

Type

S-4

is

at

the

end

of

the

Me-

chanical

Parts

List

pullout

pages.

Type

S-4

SECTION

2

OPERATING

INSTRUCTIONS

Change

information,

if

any,

affecting

this

section

will

be

found

at

the

rear

of

the

manual.

General

Information

This

section

provides

the

basic

information

required

for

operation

of

the

Type

S-4

Sampling

Head,

including

installa-

tion

and

First

Time

Operation.

The

Type

S-4

can

be

used

on

an

extender

cable

without

compromising

the

response

of

the

measurement

system.

Sig-

nals

are

applied

to

the

50

Q

input

of

the

sampling

head

through

a 3

mm,

50

©

coaxial

connector

located

at

the

cen-

ter

of

the

front

panel.

Unity

loop

gain

can

be

obtained

with

input

signals

of

up

to

0.5

volt

(peak-to-peak).

Unity

loop

gain

ensures

the

most

accurate

displays,

of

particular

importance

during

fast

changes

in

input

signal

amplitude.

See

the

Basic

Sampling

Principals

Section

of

your

sampling

unit

manual

for

further

information.

The

Type

S-4

may

be

used

with

input

signals

up

to

1

volt

(peak-to-peak).

Specifications

for

the

Type

S-4

Sampling

Head

are

given

in

Section

1

of

this

manual.

NOTE

Attenuators,

with

threaded

3

mm

connectors,

are

available

as

optional

accessories.

These

attenua-

tors

are

useful

in

reducing

the

amplitude

of

large

signals.

Other

optional

accessories

with

3mm

connectors

include

coaxial

cables,

a

50

termi-

nation,

and

adapters

for

interconnecting

various

types

of

connectors.

Refer

to

your

Tektronix

cata-

log

or

contact

your

local

Tektronix

Field

Engineer

or

Representative

for

further

information

about

optional

accessories.

Installing

the

Type

S-4

Sampling

Head

Fig.

2-1

shows

the

Type

S-4

partially

installed

in

a

Type

352

Sampling

Unit

with

a

Type

564

Oscilloscope

and

a

Type

3T2

Random

Sampling

Sweep

unit.

The

sampling

head

(or

heads)

can

be

plugged

into

the

sampling

unit

as

shown,

or

used

remotely

on

a

special

extender

cable.

Three and

six

foot

extender

cables

are

available.

Order

the

three

foot

extender

cable

by

Tektronix

Part

No.

012-0124-00,

or

the

six

foot

extender

cable

by

Tektronix

Part

No.

012-0125-00.

Con-

tact

your

local

Tektronix

Field

Engineer

or

Representative

for

price

and

availability

of

these

optional

accessories.

To

insert

the

Type

S-4

into

a

compartment

of

the

sampling

unit,

proceed

as

follows:

1.

Pull

the

latch

knob

(Fig.

2-1)

outward

from

the

front

panel

(the

latch

knob

will

push

out

normally

when

the

unit

is

inserted

if

the

knob

is

left

free

to

move).

2.

Insert

the

Type

S-4

slowly

into

the

compartment,

so

the

two

plastic

guides

in

the

compartment

engage

the

S-4.

®

Fig.

2-1.

Inserting

the

Type

S-4

Sampling

Head

in

the

sampling

unit.

3.

Push

the

Type

S-4

completely

into

the

compartment.

4.

Push

the

latch

knob

to

lock

the

Type

S-4

in

place.

To

remove

the

Type

S-4

from

the

compartment,

pull

the

latch

knob

away

from

the

front

panel,

then

pull

the

unit

from

the

compartment.

To

use

the

Type

S-4

on

an

extender

cable,

install

as

follows:

1.

Pull

the

latch

knob

located

on

the

head

end

of

the ex-

tender

cable

outward

from

the

panel

(the

latch

knob

will

push

out

normally

when

the

extender

is

inserted

if

the

knob

is

free

to

move).

2.

Insert

the

extender

cable

head

end

slowly

into

the

de-

sired

compartment

in

the

sampling

unit

so

the

two

plastic

guides

in

the

compartment

engage

the

unit.

3.

Push

the

head

completely

into

the

compartment.

4.

Push

the

latch

knob

to

lock

the

extender

cable

head

end

in

place.

5.

Connect

the

Type

S-4

to

the

other

end

of

the

extender

cable

in

a

similar

manner,

and

set

the

latch

knob

to

hold

it

in

place.

2-1

Operating

Instructions—Type

S-4

6.

To

remove

the

Type

S-4

from

the

extender

cable,

pull

the

latch

knob

on

the

front

panel

of

the

Type

S-4,

and

re-

move

the

unit

from

the

extender

cable.

7.

To

remove

the

extender

cable

head

from

the

sampling

unit

compartment,

pull

the

latch

knob

otuward

from

the

front

of

the

panel,

then

pull

the

unit

free.

Mating

The

vertical

deflection

factor

and

the

sampling

system

loop

balance

(adjusted

by

the

Gate

Bal

control)

should

be

adjusted

when

mating

a

Type

S-4

to

a

sampling

unit.

The

mVOLTS/DIV

label

on

the

Type

S-4

names

the

deflec-

tion

factor

units

of

the

sampling

unit

Units/Div

switch.

For

example,

with

the

Type

S-4

installed

in

a

Type

382

and

the

Units/Div

switch

set

at

100,

each

major

division

of

CRT

de-

flection

corresponds

to

100

millivolts

of

input

signal

(when

the

Variable

control

is

in

the

Cal

position).

The

deflection

factor

is

mated

to

the

indicator

oscilloscope

CRT

by

adjust-

ing

the

sampling

unit

Gain

control.

Refer

to

the

sampling

unit

manual

for

its

Gain

adjustment.

The

Gate

Balance

adjustment

of

the

Type

S-4

is

not

great-

ly

affected

when

the

sampling

head

is

changed

from

one

sampling

unit

to

another,

or

is

operated

on an

extender

cable.

However,

for

precise

offset

measurements,

the

Gate

Balance

control

must

be

readjusted

whenever

such

a

relo-

cation

is

made.

Location

of

the

control

and

details

of

its

adjustment

are

given

below

under

the

heading

First

Time

Operation.

FIRST

TIME

OPERATION

In

addition

to

the

Type

S-4,

this

procedure

utilizes

a

Type

S-50

Pulse

Generator,

Type

3S2

Dual-Trace

Sampling

Unit,

Type

312

Random

Sampling

Sweep,

and

a

Type

564

Storage

50

Trigger

input

2ns

Flexible

3mm

coaxial

cable

Trigger

cable

Fig.

2-2.

Equipment

setup

used

during

First-Time

Operation.

2-2

Oscilloscope.

See

Fig.

2-2.

The

Type

3T2

Random

Sampling

Sweep

permits

viewing

the

signal

in

advance

of

the

trigger-

ing

event.

Such

sampling

sweep

trigger

lead-time

is

required

when

using

the

Type

S-4

with

the

Type

3S2

for

viewing

fast

pulses

without

a

pretrigger.

The

built-in

pretrigger

circuit

of

the

Type

S-50

permits

sequential

sampling

units,

such

as

the

Type

375

or

Type

3T6,

to

operate

at

their

faster

sweep

rates.

Setup

Information

1.

With

the

Type

564

Power

switch

off,

insert

a

Tektronix

Type

352

Sampling

Unit

into

the

vertical

channel

compart-

ment

(left)

and

a

Tektronix

Type

3T2

Random

Sampling

Sweep

unit

into

the

horizontal

channel

compartment.

2.

Insert

the

Type

S-4

into

the

Channel

A

compartment

(left)

of

the

Type

352

leaving

the

latch

knob

free

to

move.

Once

the S-4

is

seated,

push

the

latch

to

lock

it

in

place.

3.

Insert

the

Type

S-50

into

the

Channel

B

compartment

(right)

of

the

Type

3S2

leaving

the

latch

knob

free

to

move.

Once

the

S-50

is

seated,

push

the

latch

to

lock

it

in

place.

4.

Connect

the

Type

S-50

output

connector

to

the

Type

S-4

input

connector

using

a

2

ns

section

of

flexible

coaxial

line.

See

cable

bending

limits

discussed

under

Cable

and

acces-

sory

Considerations

later

in

this

section.

NOTE

Connectors

at

both

ends

of

the

coaxial

cable

should

be

firmly

connected

to

mating

connectors

or

accessories.

Tighten

slightly

more

than

finger

tight

using

a

°/15

inch

wrench.

A

good

connection

is

necessary

to

minimize

reflections

at

the

junction

of

connectors.

5.

Connect

Pretrigger

Out

of

the

Type

S-50

to

the

50

2

Trigger

Input

of

the

Type

372.

6.

Set

the

Intensity

control

on

the

Type

564

fully

counter-

clockwise.

7.

Connect

the

Type

564

to

the

power

line

and

set

the

Power

switch

to

On.

8.

Allow

about

5

minutes

warmup

so

the

units

reach

oper-

ating

temperature

before

proceeding.

9.

Set

instrument

controls

as

follows:

TYPE

352

Display

Mode

CHA

Normal-Smooth

Normal

Horiz

Compatibility

Sw.

Sampling

Channel

A

controls

Position

Midrange

DC

Offset

Midrange

(5

turns

from

one

end)

Units

/Div

200

Variable

Cal

Invert

Push

in

Dot

Response

Midrange

Operating

Instructions—Type

S-4

TYPE

372

Time

Position

Midrange

Horiz

Position

Midrange

Samples/Div

9

o'clock

position

Samples/Div

Sw

Variable

Display

Mode

Normal

t

Start

Point

Before

Trigger

t

Sweep

Rate

100

ns/Div

a

Range

1

ps

:

Dsiplay

Mag

x1

t

i

+Frys

Time

Magnifier x1

portion

jj

Variable

Cal

‘poe

| |

Trigger

Source

Ext

P|

Trig.

Sensitivity

Fully

clockwise

TYPE

564

Astigmatism

Midrange

Focus

Midrange

Intensity

Fully

counterclockwise

Upper

and

Lower

Screen

Non-Store

10.

Advance

the

Type

564

Intensity

control

until

the

trace

brilliance

(free

running

sweep)

is

at

the

desired

viewing

level.

Adjust

Astigmatism

and

Focus

controls.

11.

Center

the

trace

on

the

graticule

with

the

Type

382

“A”

Position

control

and/or

the

DC

Offset

control.

12.

Adjust

the

Type

312

Trigger

Sensitivity

and

Time

Posi-

tion

controls

for

a

stable

triggered

display

of

the

Type

S-50

:

|

output

pulse.

See

Fig.

2-3A

(displayed

signal

amplitude

has

Sages

been

adjusted

to

5

divisions

by

turning

the

Type

3S2

i

gor

foot

Channel

A

Variable

control).

Display

Characteristics

of

Fastrise

Input

Pulses

In

Fig.

2-3A

the

displayed

pulse

shows

overshoot

at

the

end

of

the

fastrise

portion

of

the

pulse.

This

overshoot

is

normal

when

using

the

Type

S-4

together

with

a

fastrise

pulse

generator

such

as

the

Type

$-50.

Since

the

0%

to

100%

amplitude

of

the

pulse

is

5

divisions,

each

division

represents

20%.

In

Fig.

2-3A

the

overshoot

appears

to

have

an

amplitude

of

approximately

0.4

divisions

or

8%.

The

preshoot

portion

of

the

Type

S-50

output

pulse

is

the

relatively

slow

rise

signal

driving

the

Type

S-50

output

tunnel

diode.

The

fastrise

portion

occurs

as

the

output

tunnel

di-

ode

switches.

Thus,

the

region

labeled

as

the

preshoot

por-

tion

of

the

pulse

in

Fig.

2-3A

is

apparently

much

slower

than

the

fastrise

portion.

The

presence

of

several

dots

indicates

samples

taken

during

the

preshoot,

and

the

absence

of

samples

during

the

fastrise

portion

indicates

the

difference

in

risetime.

The

appearance

of

these

portions

of

the

Type

S-50

output

pulse

at

a

faster

sweep

rate

is

shown

in

Fig.

2-3B.

(C)

Determining

displayed

risetime.

Set

Type

3T2

Range

switch

at

100

ns

and

Time

Magnifier

to

X10.

Set

the

Type

312

Start

Point

switch

to

With

Trigger.

Turn

the

Type

312

Time

Position

control

until

a

display

simi-

lar

to

that

of

Fig.

2-3B

is

visible.

This

waveform

shows

that

after

a

rather

gradual

rise

requiring

about

5

ns

(5

divisions)

Fig.

2-3.

Fastrise

pulse

displays.

Operating

Instructions—Type

S-4

the

signal

amplitude

suddenly

increases

by

approximately

500

mV.

The

displayed

pulse

of Fig.

2-3B

is

typical

of

the

Type

S-50

and

Type

S-4

combination.

In

Fig.

2-3B

the

aberration

occurring

approximately

4.5

ns

after

the

fastrise

portion

of

the

pulse

is

a

result

of

a

reflec-

tion

at

the

input

gate

of

the

Type

S-4.

A

portion

of

the

fast-

rise

part

of

the

pulse

traveling

from

the

Type

S-50,

through

the

2

ns

length

of

coax

and

through

the

Type

S-4

input

con-

nector

to

the

input

gate,

is

reflected

back

to

the

Type

S-50.

This

round

trip

requires

approximately

4.5

ns

when

the

Type

S-50

and

Type

S-4

are

interconnected

with

a

2

ns

section

of

coaxial

line.

Adding

a

second

2

ns

section

of

line

in

series

with

the

first

would

result

in

the

reflection

being

displayed

4ns

(2

X

2ns)

later,

or

8.5ns

after

the

fastrise

portion

of

the

pulse.

Determining

Displayed

Risetime

1.

Set

the

fastrise

portion

of

the

displayed

pulse

to

grati-

cule

center,

as

shown

in

Fig.

2-3B,

using

the

Time

Position

control

of

the

Type

372.

2.

Change

the

Type

3S2

deflection

factor

to

100

mV/Div

(Variable

at

CAL).

3.

Vertically center

the

fastrise

portion

of

the

displayed

pulse using

the

Type

3S2

Channel

A

Offset

control.

4.

Set

the

Type

312

Time

Magnifier

at

X50 and

readjust

the

triggering

for

minimum

jitter

using

the

Type

312

Sensiti-

vity

control.

5.

Set

the

Type

3T2

Display

Mag

at

X10

and

carefully

adjust

the

Time

Position

control

for

a

display

similar

to

that

of

Fig.

2-3C.

In

order

to

accurately

determine

the

displayed

risetime

the

display

should

be

photographed

or

stored

(on

a

Storage

Oscilloscope

CRT)

to

permit

careful

analysis.

To

store

the

display,

set

the

Type

3T2

Display

Mode

to

Single

Swp.,

the

Type

554

upper

and

lower

screen

for

storage,

and

push

the

Type

3T2

Single

Sweep

Start

pushbutton.

The

pulse

risetime

is

found

by

determining

the

horizontal

distance

between

the

10%

and

90%

amplitude

points

and

multiplying

this

distance

by

the

Time/Div

setting

of

the

sampling

sweep

unit.

It is

recommended

that

the

0%

to

100%

amplitude

be

adjusted

to

exactly

5

divisions

using

the

Type

382

Variable

control,

and

the

display

vertically

center-

ed

using

the

Type

382

DC

Offset

control.

This

will

position

the

0%

point

2.5

divisions

below

graticule

center

and

the

100%

point

2.5

divisions

above

graticule

center.

The

10%

amplitude

will

then

appear

2

divisions

below

graticule

cen-

ter

and

the

90%

point

2

divisions

above

graticule

center.

More

information

on

locating

the

0%

and

the

100%

points

of

the

displayed

waveform

is

given

later

in

this

section.

Gate

Balance

Adjustment

The

Type

S-4

Gate

Balance

may

occasionally

require

re-

adjustment.

The location

of

the

control

is

shown

in

Fig.

2-4.

Channel

A

sampling

head

can

be

adjusted

while

on

an

ex-

tender

cable

or

when

inserted

in

the

sampling

unit.

In

order

to

adjust

the

Gate

Balance

of

a

Type

S-4

located

in

the

Channel

B

compartment

of

the

sampling

unit,

it

is

necessary

to

remove

the

oscilloscope

side

panel

and any

sampling

head

plugged

into

the

Channel

A

compartment.

2-4

—

Type

S-4

Sampling

Head

Fig.

2-4.

Gate

Balance

location.

1.

Connect

a

bench

multimeter

set

for

approximately

30

V

full

scale

between

ground

and

the

Type

3S2

Channel

A

Offset

jack.

2.

Adjust

the

Type

382

DC

Offset

control

until

the

multi-

meter

reads

0

volts.

3.

Increase

the

meter

sensitivity

and

repeat

the

adjustment

for

greater

accuracy.

4.

Disconnect

the

semi-rigid

cable

from

the

Type

S-50,

leaving

the

other

end

of

the

cable

connected

to

the

Type

S-4

input

connector.

5.

Turn

the

Type

312

Trigger

Sensitivity

control

clockwise

to

free-run

the

trace.

NOTE

Operating

the

sampling

head

without

the

input

connector

terminated

by

a

50

©

resistor

or

coaxial

cable

may

cause

a

vertical

shift

of

the

zero

signal

baseline

by

a

few

millivolts.

This

is

caused

by

the

strobe

kickout

signal

being

reflected

from

the

open

input

connector,

and

arriving

back

at

the

sampling

gate while

it

is

conducting.

Because

of

this,

termin-

ate

the

input

circuit

when

setting

the

display

zero

reference

point.

Also

use

a

15cm

airline,

or

a

cable

providing

at

least

500

ps

of

delay,

between

the

Type

S-4

input

and any

tunnel-diode

genera-

tor

or

circuit

that

is

sensitive

to

signals

entering

its

output

circuit.

6.

Switch

the

Type

382

Units/Div

control

throughout

its

range,

adjusting

the

Type

S-4

Gate

Balance

control

for

a

trace

shift

of

not

over

one

division

as

the

Units/Div

control

is

switched

from

one end

to

the

other.