Tektronix 491 User manual

product

modification

050

0692

()2

(' )

M21303

M22940

BAND

OSCILLATOR

REPLACEMENT

For

TEKTRONIX®

Type

491

Spectrum Analyzers

Serial

Numbers

B010000-B272355

I l O

Solid

State

Band

Oscillator

Assembly

119-0108-01

replaces

vacuum

tube

oscillator

119-0108-00

which

longer

available.

Use

the

new

solid

state

oscillator

necessitates

the following changes:

The

dial tape

replaced

assure

oscillator

tracking

all

bands.

A -20 Volt

Power

Supply

added

for

use with

the

new

oscillator.

coupling

and

osci

tor

mounting brackets

and

hardware are replaced to

accommodate

the

changed dimension

the

new

oscillator

assembly.

1974

, Tekt

ronix,

Inc.

All

Rights Reserved. 7-23-75

Supersedes 050-0692-01

TEKTRONIX

SCOPE-MOBILE

and

are

registered trademarks

ektron

Inc.

"'?

1~1

Type

Page

PARTS

INCLUDED

PARTS

REPLACEMENT

KIT:

Quantity

Part

Number

Description

(1ea)

l ea

4 ea

l ea

1 ea

(l ea)

1 ea

l ea

2 ea

l ea

2 ea

1 ea

l ea

1 ea

*NOTE:

119-0108-01

175-1529-00

175-1530-00

211-0008-00

407-1545-00

407-1546-00

670-0523-08

175-1531-00

175-0998-00

175-0999-00

210-0203-00

211-0021-00

211-0098-00

331-0376-00

361-0525-00

376-0029-00

376-0099-00

384-1265-00

386-1135-01

670-3500-01

670-4193-01

Assembly

Oscillator*

consisting

of:

Osci1lator

Cable,

50~

coax, 175-0323-00, 9 inches

w/131-0375-00

and

w/131-0977-00

Cable,

50~

coax, 175-0323-00, 6 inches

w/131-0375-00

and

w/131-0977-00

Screw, 4-40 X .250

Barcket, angle,

oscillator

front

Bracket, angle,

oscillator

rear

Wire,

#22

stranded 175-0527-00 4 inch white

Wire,

#22

stranded 175-0527-00 3 inches white-black

Assembly,

Oscillator

Connector

Circuit

Board,

consisting

of:

Circuit

Board,

Oscillator

Connector

Wire, ribbon

w/3

wires

#26

stranded

w/3

131-0707-00

connectors

and

w/l 352-0161-00 holder

one

end

only.

White-brown

and

White-red

inches long soldered

circuit

board

and

White-orange 7 inches long

from

holder end.

Wire,

#22

stranded 175-0527-00 4 inch White-red

Wire,

#22

stranded 2 3/4 inches Wht-blk-yel

w/2

131-0371-00 connectors

Wire,

#22

stranded 2 inches

t-brn

w/l

131-0707-00 connector

Lug,

so1

r S

E-6

long

Screw, 4-40 1.250

Screw, button

head

4-40 x .375

Tape, Frequency

Spacer, Delrin®

.781

inches long x .25

Coupling

shaft,

rigid

.312

x .5

x .128

Coupling

shaft,

flex

.437 long x .250

Shaft

extension,

.450 long x .125

Plate,

Oscillator

mounting

Circuit

Board, -20 Volt

Power

Supply

Circuit

Board, Connector

The

front

and

rear

angle brackets are fastened to the

Band

Osci1lator

for

purposes

identification

and

orientation.

They

must

removed

before the

oscillator

can

insta1led.

Save

hardware.

® Delrin

registered

trademark

Dupont

Nemours

Inc.

Page

2 of 9 050-0692-02

INSTRUCTIONS:

DISCONNECT

THE

INSTRUMENT

FROM

ITS

POWER

SOURCE!

CAUTION

Removing

reinstalling

the instrument dust cover

may

hazardous

when

the

instrument

slid

in or out

the dust cover.

Remove

reinstall

the dust

cover

follows:

ace

the accessory cover

the instrument. Stand the instrument

vertically

the

front

cover.

Remove

the four

plastic

feet

and

the

two

thumbscrews

and

slide

the cover

off

the instrument.

REMOVE

OSCILLATOR

ASSEMBLY

( )

Remove

the

Tuning

knob

and

the

Band

Selector

Switch

knob.

Remove

the screw

below

the tuning

shaft.

Disconnect the following wires

from

the pin connectors

the

connector block

the

chassis:

( ) 2. White-blue wire

from

()

3. White-violet wire

from

( ) 4. White-black wire

from

Disconnect the wires

from

the

Oscillator

connector

Circuit

Board

that

connect to the

TIME/DIV

Switch

follows:

( ) 5.

White

wire. (Unsolder

shield

white-black

coax

from

pin connector).

( ) 6. White-black-brown wire.

( )

White-brown-green-brown.

( ) 8. White-black wire. (Unsolder

center

of white-black

coax

from

Pin connector).

()

9. Disconnect

all

the sub-miniature

right

angle coaxial connectors

from

the

oscillator

assembly.

facilitate

reassembly label the

coax

cables

and

connectors.

( ) 10.

Remove

the

Band

Switch bracket mounting screws

which

are

accessible

from

the bottom, (Note:

You

may

have

remove

the

rail

mounting bracket in

order to reach the top screw)

and

the

two

nuts

that

fasten the

driver

gear assembly

the

front

panel,

and

remove

the

oscillator

assembly.

Page

9 050-0692-02

REMOVE

THE

BAND

OSCILLATOR

( )

Unsolder

the

Band

oscillator

filament

leads*.

One

from

the

Band

'B'

oscillator

and

one

from the

oscillator

connector board.

2. Unsolder band C

B+

lead

(orange wire) from connector board.

3. Loosen the

set

screws

the

Band

oscillator

.drive

flexible

coupler*.

Loosen

the

collet

the

Band

oscillator

tuning

shaft.

5. Loosen the

set

screw (j) (See Fig. 2 page 9)

that

fastens

the

front

band svJitch

lever

the

coupling rod. @ .

Remove

the

four

4-40 screws

@,;

that

fasten

the

dial

housing to the

front

oscillator

mounting

plate*

;3·,

and

remove

the

dial

housing.

Remove

the

two

screws

that

fas

ten

the

back end

the

Band

osci

tor

the

rear

sup

port

bracket

(6--;.

,_...,

8. Observe

the

orientation

the

front

mounting

plate

(3J

and

remove

two

screws,

one

flat

head and

one

pan

head,

that

fasten

the

Band

oscillator

the

front

mounting

bracket.

Remove

the

two

socket

head screws

~6)

that

fasten

the

front

mounting

Plate

the

Band

oscillator,

and

remove

the

Band

oscillator,

and

the

front

mounting

plate*.

INSTALL

NEW

BAND

OSCILLATOR

( )

Temporarik

remove

the

two

screws

r28J

that

fas

ten the band switch

bracket

the

Band

osci

l'lftor

rear

support.

Fas

ten the

Band

osci

tor

rear

support

angle

bracket

over

the

band switch

bracket

with the hardware

just

removed.

( ) 2. Fasten the

new

front

oscillator

mountil']g

plate

m to the

Band

oscillator

using the hardware removed

Step

B..:-g:

( ) 3. Reins

tall

the

al housing

ins

tall

the

two

top screws

that

fas

ten

the di al housing to the

new

front

oscil

tor

mounting pl

ate.

NOT

TIGHTEN

COLLET

BAND

OSCILLATOR.

( ) 4. Fasten the

Band

oscillator

front

angle

bracket

the

bottom holes

the

dial

housing and

replace

the bottom

left

mounting screw with

the button head screw.

* Discard.

Part

will

not

used in

new

assembly.

Page

9 050-0692- O2

INSTRUCTIONS

: (ContI d)

( )

Slide

the

new

shaft

coupler

over

the

Band

oscillator

dial

assembly

drive

shaft,

put

the

extension

shaft

into

the

shaft

coupler.

Install

half

the

new

flexible

coupler

the

shaft

extension

@ and

the

other

half

the

Band

"C"

oscillator

drive

shaft.

Install

the

Band

"C"

oscillator*

follows:

NOTE:

sure

the

tor

turned

the

high end

(fully

clockwise)

the

Band.

Align

the

two

halves

the

flexible

coupler@

and

insert

the

center

part

the

flexible

coupler.

Fasten

the

Band

"C"

oscillator

place

with

the

4-40 X .250 inch

screws

@·

( ) 8. Reconnect

the

band

switch

lever

the

coupling

rod @

the

dial

housing.

()

9. Align the

Band

"C"

Oscillator

follows:

Temporarily

reinstall

the

Tuning

knob

the

main

dial

drive

shaft

and check

for

smooth

operation

the

Tuning knob.

The

Band

"C"

Oscillator

rear

support

fastened

the

back end

the

Band

"B"

Osei

tor

a 1

u•

shaped

bracket.

This

bracket

allows

mechanical

adjustment

two

directions.

Side

adjustment

accomplished

loosening

the

set

screw,

one

each

side,

and

tightening

the

set

screw

the

other

side.

REPLACE

DIAL

TAPE

( )

Turn

the

Tuning di al**

all

the

way

the

high

end,

fully

clockwise.

( ) 2.

Remove

the

dial

window

mounting screws

and

remove

the

dial

window.

( ) 3. Manually run

the

dial

tape

off

the

right

hand

spool,

and

pull

the

tape

off

the

left

hand

spool.

( )

Wind

the

new

dial

tape

the

low

end

the

outside.

Thread

the

dial

tape

onto

the

left

hand spool and wind

all

the

tape

on.

Then

slip

the

high end

over

the

right

hand spool and

turn

until

the

high end

the

dial

the

center

the

window, and

reinstall

the

di a1 wi n

dow.

**The

collet

the

Band

"A"

Oscillator

and the

set

screws

the

Band

"C"

Oscillator

shaft

coupler

should

both

loose.

Page 5

9 050-0692- 02

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

-----------

INSTRUCTIONS:

(Cont

REPLACE

CONNECTOR

CIRCUIT

BOARD

( )

Unsolder

all

the wires

from

the

connector

circuit

board

the

Phase

lock chassis

and

replace the connector

circuit

board with the

new

Connector

circuit

board,

from

the

kit,

and

wire

follows:

Wire

Color

Wire

Color ----·

A white

and

#22

bare

white-black

wire to pin B F white-brown-red

B Shield for pins G white-brown-green

C &D H white-black-brown

Red

I* white-vio1

Black

white-blue

REPLACE

OSCILLATOR

CONNECTOR

BOARD.

SEE

FIG.

( )

Unsolder

all

the wires

from

the

oscillator

connector

circuit

board.

( )

Remove

the

oscillator

circuit

board

mounting

screws

and

replace the

circuit

board with the

new

board

and

wire

follows:

( ) 3. Solder the White-red wire

(See

Ftg. 1) to the

-20VDC

termina1

the

Band

osci1

lator.

( ) 4. Solder the white wire

from

the

ground

connection

the

Band

oscillator

to the

grounded**

side

the

Band

filament.

( ) 5. Solder the white-black wire

from

the

AFC

terminal

the

Band

1C1

oscillator

to the

AFC

terminal

the

Band

1B1

oscillator.

( )

Connect

the remaining wires

shown

in the drawing.

FIGURE

WHT-BLK--

The

white-black,

white-violet,

and

white-blue wires will

connected in

step G4-6.

Terminal

toward

the back.

CHECK

WITH

OHMETER

SURE.

Page

6 of 9 050-0692-02

INSTRUCTIONS:

(Cont'd)

REINSTALL

OSCILLATOR

ASSEMBLY

( ) 1. Reinstall the

oscillator

assembly in the instrument using the hard-

ware

removed

in Step

A-10.

Two

6-32

screws in the

back

end

and

two

6-32

nuts in the

front.

( ) 2. Reinstall the 4-40 screw

below

the tuning

shaft

that

fastens the

dial housing to the

front

panel.

( )

Reinstall the

Tuning

knob

and

the

Band

Switch Lever,

and

switch the

Band

Switch to

check

for proper

knob

position.

The

knob

position

can

adjusted

moving

the switch

lever

the coupling rod.

Reconnect wires to connector block

chassis

follows:

( ) 4. White-blue wire to

( )

White-violet wire to

( )

White-black wire to

Connect

wires to

oscillator

connector board terminals

from

top to

bottom

follows:

( )

White

wire (ground).

( ) 8. White-black-brown wire.

( )

White-brown-green wire.

( ) 10. White-black wire.

( ) 11. Reconnect the sub-miniature coaxes

removed

in Step

A-9

and

connect the

coax

from

the

output

the

Band

oscillator

J45

the

Multiplexer

and

connect the

Phase

Lock

connector

the

Band

osc-

illator

to Jll40

the

Phase

Lock

Assembly.

( ) 12.

Dress

the three wire ribbon cable

from

the

oscillator

circuit

board

back

and

through the chassis. Solder the white-orange wire to the

ground

solder

lug

the

power

supply chassis near

C954.

The

connector will

connected to the

new

-20 Volt

Power

Supply in

Step

H-8.

Page

9 050-0692-02

INSTRUCTIONS:

(Cont'd)

INSTALL

THE

-20VOLT

POWER

SUPPLY

FOLLOWS:

( ) 1. Place the instrument

the

workbench

bottom side up, release the lock

the

Control

Circuit

Board

and

swing

open

to gain access to

the

Power

Supply

Circuit

Board.

{ ) 2.

Add

the

solder

lug to the bottom

mounting

screw of the

RFI

filter.

Solder the white-brown wire,

from

the

kit,

this

solder lug. Other

end

will

connected in Step

H-7.

( ) 3.

Remove

the

two

mounting

screws

from

the

Power

Supply

Circuit

Board

near the

RFI

filter.

( ) 4. Disconnect the white-black-yellow wire

from

the

Power

Supply

Circuit

Board.

Connect

the 2 3/4 inch white-black-yellow wire

from

the

kit

AA.

These

b-10 wires

connect to the

new

circuit

board in Step

H-6.

( ) 5.

Mount

the -20Volt

Power

Supply Circuit

Board

above

the

Power

Supply

Circuit

Board

the

.781

inch spacers

and

fasten in place with the

1.250 inch

4-40

screws in the holes vacated in Step

D-1.

( )

Connect

the

two

white-black-yellow wires mentioned in Step

H-4

and

the -20Volt

Power

Supply.

( )

Connect

the white-brown wire

installed

in Step

H-2

Cof the

-20Volt

Power

Supply.

( ) 8.

Connect

the

two

wire ribbon connector

from

the

oscillator

connector

board to

P920

the -20Volt

circuit

board.

( ) Refer to the Calibration Procedure in your

Instruct~on

Manual

and

the supplemental Calibration procedure in the Instruction

Manual

Modificat.ion

Insert

the

back

thjs

kit

and

recalibrate

required.

( )

For

future reference fasten the Modification

Insert

in your Instruction

Manual.

Page

9 050-0692-02

ITEM

PART

NUMBER

331-0176-03

175-1529-00

386-1139-00

119-0108-01

407-0295-00

407-0294-00

213-0075-00

260-0821-00

337-0880-00

119-0063-01

175-1530-00

407-1545-00

384-0425-00

211-0062-00

211-0012-00

210-0004-00

211-0504-00

407-1546-00

210-0006-00

211-0098-00

213-0004-00

210-0405-00

210-0053-00

131-0391-00

176-0124-00

211-0564-00

175-1531-00

211-0008-00

670-0523-08

211-0116-00

376-0029-00

376-0099-00

384

1265-00

QUANTITY

Req.

DESCRIPTION

Dial

Assembly

Tape

Cable

Assembly,

Elec

(LO)

Plate

Mounting

Oscillator

Assembly,

Support,

Oscillator

Bracket, Oscillator

Screw,

4-40 x .094 Socket

Head

Switch

Lever

Shield

Rotary

Switch

Oscillator,

Cavity

Cable

Assembly,

Elec

(Lock)

Bracket,

Angle

(Oscillator Front)

Rod,

Coupling

Screw, 2-56 x .312

Screw,

4-40 x .375

Lockwasher,

Internal

Screw,

6-32 x

250

Bracket,

Angle

(Oscillator

Rear)

Lockwasher,

Internal

Screw,

4-40 x .375 Button

Head

Screw,

6-32 x .188 Socket

Head

Set

Hex

Nut,

2-56 x

.188.

Lockwasher,

Split

Connector,

coax

Wire, .0508

#16

AWG

Dia,

Tinned

Screw,

6-32 x .375 Socket

Head

Cable,

Assembly,

Elec.

Screw,

4-40 x .250

Oscillator Connector Circuit

Board

Screw,

4-40 x .312

Assembly

washer

Coupler

Shaft

r.;:vL.o...icr

u~.

CN-,..)

~·~

FIG.

Fig. 2

050-0692-01

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