THORENS PC 650 - Heads and Electronics; Head Maintenance and Alignment

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a)

The

lower

edge

of

the

head

bracket

(3191415)

should

cover

half

the

reference

hole

‘’F”

behind

it

when

electric-

ally

engaged

(Fig.

6).

b)!f

the

adjustment

is

incorrect,

loosen

the

mounting

screws

of

the

holding

magnet

(3192005)

and

reposition

the

magnet

as

required

(Fig.

7).

c)

Tighten

the

screws

and

recheck

the

adjustment.

.

Tape

Tension

Adjustment

a)

Insert

a

tension

measuring

(“torque

meter’’)

cassette.

b)

In

the

PLAY

mode,

adjust

the

winding

tension

to

a

value

between

40

and

45

g-cm

with

R

1416

(on

board

VM

14).

c)

The

unwinding

tension

should

lie

between

8

and

10

g-cm.

.

Tape

Speed

Adjustment,

Speed

Variation

Check

a)

Insert

a

cassette

recorded

with

a

sinewave

signal,

the

frequency

of

which

is

determined

by

the

method

of

measurement

employed,

as

follows:

—

3150

Hz

for

the

use

of

a

wow

and

flutter

meter.

—

the

mains

frequency

(50

Hz

or

60

Hz)

for

adjust-

ments

with

an

oscilloscope

using

Lissajous

figures.

Observe

appropriate

safety

requirements!

—

any

suitable

audio

frequency

for

the

use

of

a

fre-

quency

counter.

b)

In

the

PLAY

mode,

adjust

the

speed

by

turning

the

screw

on

the

rear

of

the

drive

motor

(Fig.

8).

The

pro-

tective

covering

must

be

penetrated

with

the

adjusting

screwdriver,

and

the

printed

circuit

board

VM

6/A

be-

hind

the

motor

can

be

removed

to

ease

access

to

the

screw.

c}

Should

wow

and

flutter

readings

exceed

published

spe-

cifications,

check

the

condition

of

the

pressure

roller

(pressure

arm

3190565)

and

the

pressure

spring

(3030635)

(Fig.

7).

ERASE

AND

RECORD/PLAYBACK

HEADS

Erase

Head

Replacement

A

gradual

degeneration

of

erase

characteristics

generally

indicates

the

necessity

of

replacing

the

erase

head

(Fig.

9,

3030605).

a)

Verify

first

that

the

correct

erase

voltage

(app.

37

Vrms

for

BIAS/EQ

position

"FeCr”,

28

V

for

Fe”,

and

45

V

for

"Cr’,

100

KHz)

is

present

at

the

head

terminals

with

an

unrecorded

cassette

inserted

and

the

REC

button

de-

pressed.

b)

Unsolder

the

connecting

cable

at

the

head.

c)

Remove

the

two

mounting

screws

and

replace

the

head.

d)

Readjust

the

azimuth

setting

of

the

record/playback

head

according

to

Section

9.

e)

Readjust

the

Dolby

playback

filter

according

to

Section

14.

Fig

7

3192005 3190565

F

3062335

3030605

Azimuth

Fig.

9

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