Telefunken M 204 E - Mechanical Adjustments and Operation; Quick Stop, Tape Speed Selector, and Capstan Bearing; Electrical Measurements and Adjustments; Head Alignment and Frequency Response Checks

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Quick

Stop

When

the

quick

stop

button

“Pause“

is

actuated,

the

left

feed

plate

assembly

is

restrained

with

the

cork

auxiliary

brake,

the

tape

transport

is

arrested

by

lift-off

of

the

rubber

pressure

roller,

and

then

the

right

take-up

plate

is

stopped

by

lift-off

of

the

friction

wheel

from

the

flywheel

disc.

A

functional

check

of

this

process

can

be

made

by

pressing

the

quick

stop

button

slowly.

If

the

given

order

of

events

is

not

maintained,

then

the

tab

(B)

which

points

from

the

quick

stop

plate

towards

the

chassis

must

be

bent

accordingly.

Adjusting

the

Tape

Speed

Selector

Mechanism

When

the

selector

toggle

lever

is

actuated,

the

metal

slider

for

the

equaliser

changeover

switch

is

moved

at

the

bottom,

and

the

switching

rocker

for

the

belt

is

moved

at

the

top.

The

metal

slider

for

the

equaliser

changeover

switch

must

move

lightly.

It

should

jump

immediately

to

the

final

setting

when

switching

over.

If

necessary,

the

glide

points

of

the

slider

should

be

lubricated

with

Molykote

Paste

G

Rapid.

The

belt

switching

rocker

must

be

adjusted

such

that

the

belt

does

not

scrape

against

the

rocker

in

either

one

of

the

two

tape

speed

settings.

If

necessary,

adjust

as

follows:

first

of

all

switch

to

19

cm/s

and

adjust

the

long

leg

of

the

switching

rocker

such

that

the

belt

runs

centrally

in

the

slots

of

the

rocker.

Then

repeat

the

same

adjustment

after

switching

over

to

9.5

cm/s,

but

in

this

case

judiciously

bend

the

adjustment

nose

of

the

toggle

lever

which

bears

against

the

switching

rocker.

Adjusting

the

Drive

Capstan

Bearing

Block

Adjustment

is

here

necessary

when

the

bearing

block

has

been

released

or

replaced.

The

drive

capstan

runs

at

the

top

in

a

plastic

prismatic

bearing

and

at

the

bottom

in

a

self-aligning

sintered

bearing.

The

capstan

has

a

play

of

about

0.5

mm

in

the

upper

bearing

as

long

as

the

drive

button

is

not

actuated.

The

drive

capstan

is

pressed

into

the

prismatic

profile

and

thereby

takes

up

its

precise

nominal

position

parallel

to

the

magnetic

heads

and

tape

guides,

only

when

the

drive

button

is

actuated

and

the

rubber

pressure

roller

pushes

the

capstan

against

its

bearing.

The

adjustment

should

be

carried

out

with

the

drive

button

(start

button)

pressed

and

with

the

screws

of

the

bearing

block

tightened

moderately.

For

this

purpose,

use

a

depth

gauge

to

measure

the

clearance

between

the

head

carrier

plate

and

the

turned

step

of

the

flywheel

disc

at

three

well

spaced

points.

If

these

clearances

are

unequal,

make

them

equal

by

adjusting

the

bearing

block

accordingly.

If

a

repair

task

makes

it

necessary

to

release

the

bearing

block,

it

is

advisable

first

of

all

to

mark

its

position

on

the

head

carrier

plate,

using

a

scriber.

Electrical

Measurements

and

Adjustments

Measuring

Equipment

Universal

Multimeter

(internal

resistance

about

50

kQ/Volt),

AF’

Signal

Generator,

AF-VTVM

or

Voltage-Calibrated

Oscillo-

scope,

AEG-TELEFUNKEN

Test

Tape

(Order

No.

50.89.107).

N.

B.:

For

signal

injection

from

the

AF

signal

generator

for

the

following

measurements,

pins

2

and

3

on

the

phono

jack

are

used

for

channel

1

and

pins

2

and

5

for

channel

2.

The

voltage

levels

here

required

are

readily

obtained

directly

from

the

AF

signal

generator,

without

special

voltage

divider.

Furthermore,

this

practice

avoids

false

readings

which

could

otherwise

result

from

ground

loops

between

the

AF

signal

generator

and

the

tape

recorder

when

injecting

signals

into

the

sensitive

input.

All

the

measurements

described

below

are

to

be

made

in

the

setting

“Stereo”

at

9.5

cm/s

tape

drive

speed.

Rocking-In

the

Record/Playback

Head

Before

inserting

the

test

tape,

degauss

the

heads

and

tape

guides.

Insert

the

test

tape,

rewind

it

completely

once

in

each

direction,

and

connect

the

VTVM

to

the

radio

jack

(pins

2

and

3

or

2

and

5).

With

the

screw

(D)

of

the

rocker

plate,

first

of

all

adjust

the

head

coarsely

during

playback

of

the

1

kHz

measuring

tone,

and

then

adjust

it

finely

during

playback

of

the

12

kHz

measuring

tone.

These

adjustments

must

be

made

separately

for

the

top

and

bottom

channel.

If

the

voltage

maximum

setting

for

the

one

channel

does

not

correspond

exactly

to

that

for

the

other

channel,

finally

set

the

head

to

a

position

about

midway

between

the

respective

maxima.

Checking

the

Playback

Frequency

Response

Insert

the

test

tape

and

connect

the

VTVM

to

the

radio

jack

(pins

2

and

3

or

2

and

5).

Take

readings

during

playback

of

the

test

frequencies

80

Hz,

1

kHz,

10

kHz,

12

kHz

(—20

dB).

The

readings

obtained

should

not

differ

by

more

than

+3dB

with

respect

to

the

reading

for

1

kHz.

Check

for

both

channels.

If

the

two

channels

give

different

readings

for

the

1

kHz

reference

signal

level

(full

level),

correct

by

adjusting

the

potentiometer

R

219.

This

matches

channel

2

to

channel

1.

Adjustments

of

the

Equaliser

Coils

and

Checking

the

Recording

Preemphases

Connect

the

AF

signal

generator

to

the

phono

jack

(pins

2

and

3)

and

the

VTVM

to

the

stereo

earphones

jack

(pins

2

and

3).

Short

circuit

points

1

and

6

of

the

oscillator

coil,

turn

up

the

drive

level

control

to

maximum

and

switch

the

unit

to

recording.

Inject

a

1

kHz

signal

at

such

a

level

(about

t0

mV)

that

the

VTVM

reads

150

mV.

Without

altering

the

input

level,

then

tune

the

AF

signal

generator

to

14.5

kHz.

Adjust

the

core

of

the

coil

L

102

for

maximum

voltage

reading.

The

voltage reading

then

obtained

on

the

VTVM

should

increase

by

about

14

to

20

dB

(to

0.75

to

1.5

V)

at

14.5

kHz,

and

by

about

0

to

3

dB

(to

150

to

220

mV)

at

50

Hz.

The

measurements

must

be

repeated

for

the

second

channel,

with

signal

injection

at

the

phono

jack

(pins

2

and

5)

and

the

VTVM

connected,to

the

stereo

earphones

jack

(pins

2

and

5).

In

this

case,

the

coil

L

202

should

be

adjusted.

Adjusting

the

Tuned

Trap

Coils,

L101

and

L201

This

adjustment

is

necessary

when

oscillator

components

or

the

erase

head

have

been

replaced.

Connect

the

VTVM

to

L

101

/

R

113

or

to

L

201/R

213

and

chassis,

and

switch

the

unit

to

recording.

Adjust

the

core

of

the

coil

L101

or

L201

for

maximum

voltage

reading.

C

131

10000

pF

top

short-circuit

here

looking

onto

the

components

side

of

the

amplifier

board

Fig.6

Short-circuiting

the

oscillator

coil

Checking

the

Frequency

Response

,,Over

Tape“

For

the

recording

process,

connect

the

AF

signal

generator

to

the

phono

jack

(2

and

3);

for

the

playback

process,

connect

the

VTVM

to

the

radio

jack

(2

and

3).

Insert

the

test

tape

and

wind

forwards

up

to

the

unrecorded

section.

Switch

the

unit

to

recor-

ding,

turn

up

the

drive

level

control

to

maximum,

and

with

an

input

voltage

of

5

mV

first

of

all

record

at

1

kHz

and

thereafter

at

14

kHz.

These

two

frequencies

should

be

reproduced

at

the

same

level

during

playback.

If

the

playback

levels

are

found

to

differ,

repeat

the

recording

after

slight

displacement

of

the

bias

trimmer

C

12

for

channel

1.

Reduction

of

the

trimmer

capacitance:

increased

treble

response

Increase

of

the

trimmer

capacitance:

decreased

treble

response

These

measurements

and

adjustments

must

be

carried

out

a

IGS

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