THORENS PC 650 - Page 9

11.
12.
13.
e)
The
voltage
at
MP
3
(L)
and
MP
4
(R)
should
lie
at
approximately
25
mV.
Should
deviations
be
regis-
tered, see Section 11.
—
The
voltage
amplification
of
the
Dolby
playback
board
VM
6/W
is
approximately
29
dB,
so
that
a
signal
level
of
about
1
mV
should
be
measured
at
points
S
612
(L)
and
S
603
(R).
—
The
frequency
response
should
remain
linear
when
the
signal
frequency
is
varied
within
the
range
specified
in
the
instruction
manual.
If
deviations
from
published
data
are
registered,
perform
the
adjustment
procedures
in
Sections
9
and
11
-
13.
f)
The
voltage
level
at
the
output
(DIN
3
and
5,
LINE
OUT
L
and
R)
should
lie
at
approximately
20
mV,
Measure the frequency response as a final check.
Playback Level Calibration
a)
Insert
a
level
calibration
cassette
recorded
with
333
Hz
(250
nW/m).
b)
In
the
PLAY
mode,
adjust
R
228
(L)
and
227
(R)
to
achieve
a
voltage
level
of
740
mV
at
MP
3
(L)
and
MP
4
(R).
Signal
Level
Meter
Calibration;
Limiter
Check
and
LED
Threshold
Adjustment
a)
Insert
an
unrecorded
cassette,
turn
the
LIMITER
switch
to
OFF,
and
press
REC
button.
b) Feed a 1KHz sinewave signal into the DIN L and R inputs.
c)
Set
the
voltage
level
at
MP
1
(L)
and
MP
2
(R)
to
580
mV
with
the
signal
generator
or
the
INPUT
level controls.
d)
Adjust
R
117
(L)
and
R
118
(R)
to
bring
the
meter
indication
to
0
dB”
(beginning
of
the
red
range).
e) Raise the input voltage level by approximately 5 dB.
f)
When
the
LIMITER
switch
is
now
turned
to
ON,
the
meter
indication
must
fall
to
between
“0
dB”
and
’’+1.5
dB”,
and the
LED’s
must
illuminate.
g) Adjust the LED switching threshold with a voltage level of 600 mV at MP 1 and MP 2. Set R 1603 (L)
and R 1604 (R) so that LED’s just begin to illuminate.
Frequency
Response
Calibration,
TEST
Generator
Adjustment
The
following
procedure
should
be
performed
in
its
entirety,
in
the
order
presented,
even
if
deficiencies
in
the
frequency
response
appear
for
only
certain
varieties
of
tape.
a)
Center
the
settings
of
both
Dolby
CAL
controls
on
the
front
panel.
b)
Insert
an
unrecorded
CrO9
cassette
(DIN
C
401
R),
set
the
BIAS/EQ
selector
to
'’Cr”’,
and
press
the
REC
and
PLAY
buttons
simultaneously.
c)
Feed
in
a
333
Hz
sinewave
signal
and
set
the
voltage
level
at
MP
1
(L)
and
MP
2
(R)
to
-30
dBm
(app.
25
mV)
with
the
signal
generator
or
the
INPUT
level
controls.
This
level
is
to
be
retained
for
the
entire
calibration
procedure.
d)
Switch
the
signal
generator
frequency
to
14
KHz.
Adjust
the
signal
level
to
-30
dBm
at
MP
3
(L)
and
MP
4
(R)
with
R
111
(L)
and
R
112
(R).
e)
Switch
back
to
333
Hz.
Adjust
the
signal
level
to
-30
dBm
at
MP
3
(L)
and
MP
4
(R)
with
R
107
(L)
and
R
108
(R).
f)
Repeat
steps
d
and
e
to
eliminate
level
differences
between
333
Hz
and
14
KHz
and
thereby
achieve
a
linear
frequency
response.
If
the
frequency
characteristic
at
high
frequencies
is
not
sufficiently
linear,
check
the
condition
of
the
record/playback
head
(3062335,
Fig.
9)
and
replace,
if
necessary,
according
to
Section
8.
g)
Depress
the
TEST
button
and
adjust
R
1513
(TEST
generator
level)
to
bring
the
signal
level
meter
in-
dication
to
0
dB”
(beginning
of
the
red
range).
h)
Insert
an
unrecorded
Fe
cassette
(Maxell
UDXL
1),
set
the
BIAS/EQ
selector
to
Fe’,
and
press
the
REC
and
PLAY
buttons
simultaneously.
i)
Adjust
R
1001
to
eliminate
level
differences
between
333
Hz
and
14
KHz
at
MP
3
and
MP
4.
Discrep-
ancies
in
level
which
may
be
observed
between
the
channels
should
be
averaged
out.
j)
Recheck
the
function
of
the
TEST
generator.
When
the
TEST
button
is
depressed,
the
"0
dB”
indi-
cation
must
approximately
be
achieved
once
again.
k)
Insert
an
unrecorded
FeCr
cassette
(Sony),
set
the
BIAS/EQ
selector
to
‘FeCr’’,
and
press
the
REC
and
PLAY buttons
simultaneously.
|)
Adjust
R
184
to
eliminate
level
differences
between
333
Hz
and
15
KHz
at
MP
3
and
MP
4.
Discrep-
ancies
in
level
which
may
be
observed
between
the
channels
should
be
averaged
out.
m) Recheck the function of the TEST generator as described in step j.