Pioneer CT-F850 User manual

CASSETTE TAPE DECK
T=F-Ss50
Y PIONEER’

MODEL CT-F850 COMES IN SIX VERSIONS DISTINGUISHED AS FOLLOWS:
HE AC 220V and 240V (Switchable)
AC 120V, 220V and 240V (Switchable)
KU AC 120V only U.S.A. mode!
KC AC 120V only Canada mode! ;
Europe model
HB AC 220V and 240V (Switchable) United kingdom model
AC 120V, 220V and 240V (Switchable) General export model
U.S. military model
e This service manual is applicable to the CT-F850/KU, KC. For servicing of the other types,
please refer to the additional service manuals.
CONTENTS
1. SPECIFICATIONS ...............0200es 3
2. FRONT PANEL FACILITIES.............. 4
3. LEVELDIAGRAM.................-05- 6
4. DISASSEMBLY ............ 0.02 eee eee 8
5. PARTS LOCATION ...............00005 11
6. BLOCK DIAGRAM ............-200000- 13
7. CIRCUIT DESCRIPTIONS
7.1 Recording and playback circuit ........ 15
7.2 Tape selector and equalizer........... 15
7.3 Level meters circuit................ 16
7.4 Dolby NR circuit ................. 17
7.5 Control circuits ..............000- 18
7.6 Muting circuits ...........020000ee 20
8. MECHANICAL ADJUSTMENTS
8.1 Pinch roller pressure adjustment ....... 25
8.2 Tape speed adjustment ............. 25
8.3 Tape guide adjustment.............. 25
9. ELECTRICAL ADJUSTMENT
9.1 Head azimuth adjustment............ 26
9.2 Playback equalizer adjustment ........ 27
9.3 Playback level adjustment ........... 27
9.4 Level meter adjustment ............. 27
9.5 Bias trap adjustment ............... 27
96 Erasure current adjustment........... 27
97 Bias adjustment ...............0-- 28
9.8 Recording frequency response......... 28
9.9 Recording level adjustment........... 29
9.10 Recording Dolby NR level adjustment... . 30
9.11 Playback Dolby NR level adjustment .... 30
10. EXPLODED VIEWS
TOET . (EXtENOn sui eeee Sie biden cae els Sa 32
10.2 Mechanism assembly 1.............-.- 35
10.3. Sub-chassis ....... 0... 2.02 e ee aes 37
10.4 Mechanism assembly 2.............. 38
11. SCHEMATIC DIAGRAMS, P.C. BOARD
PATTERNS AND PARTS LIST
11.1. Miscellaneous parts list ............. 41
11.2 Connectiondiagram ............... 42
11.3. Schematic diagram ................ 43
11.4 P.C. boards connection diagram. ....... 46
11.5 Mother assembly(RWX-302).......... 49
11.6 Power supply and control assembly ..... 53
(RWR-076)
11.7. Indicator amp assembly ............. 55
11.8 Sensing assembly ...............4. 55
11.9 Indicator assembly ..............0.. 55
11.10 Function indicator assembly .......... 56
11.11 Switch assembly ............0...00- 56
11.12 Fuse assembly ................00. 56
12: PACKING a8 .5 3 okie Oe ed bei eiaieties 57

1. SPECIFICATIONS
Systems.........-- Compact cassette, 2-channel stereo
Motors ..........-. Capstan drive; DC servo motor x 1
Reel drive; DC high torque motor x 1
Heads: ji 0 ee Sa eeene dee ears Oe ae Sendust recording/
playback combination type head x 1
Erasing head x 1
Fast Winding Time ......... Approximately 85 seconds
(C-60 tape)
Wow and Flutter........ No more than 0.04% (WRMS)
Frequency Response
—20dB Recording ;
Standard, LH tapes .............. 20 to 17,000Hz
(25 to 15,000Hz +3dB)
Ferrichrome tape .............-- 20 to 18,000Hz
(25 to 17,000Hz +3dB)
Chromium dioxide tape ...........- 20 to 18,000Hz
(25 to 17,000Hz £3dB)
Metal tape... 2... ....-2-00 0006 20 to 19,000Hz
(25 to 18,000Hz +3dB)
OdB Recording ;
Chromium dioxide tape .........-. 20 to 11,000Hz
Metal tape ............2-002-08- 20 to 14,000Hz
Signal-to-Noise Ratio. . . Dolby NR OFF; More than 59dB
Dolby NR ON ; More than 69dB
(over SkHz)
Harmonic Distortion ........ No more than 1.2% (OdB)
Inputs (Sensitivity/Maximum allowable input/Impedance)
MIC (L, R);0.3mV/100mV/10kilohms, 6mm diam. jack
(Reference MIC impedance; 250 ohms to 10 kilohms)
LINE x 2; (64mV/25V/85 kilohms) Pin jack
Outputs (Reference level/Maximum level/Load impedance)
LINE x 2; (450mV/630mV/50 kilohms) Pin jack
HEADPHONES x 1; 70mV/98mV/8 ohms, 6mm diam. jack
Semiconductors
Amplifier Section ........ Transistors x 49, ICs x 10,
Diodes x 51 (including Zener Diodes x 3, LEDs x 7)
Motor control Section ..... Transistors x 3, Diode x 1
Subfunctions
@ Dolby NR system (ON-OFF) with LED indicator lamp
© Fluorescent tube level meter (—20 to +8dB)
(Peak/Average selector) ©
Bias fine adjusting control knob
4 position tape selector (STD/METAL/CrO,/Fe-Cr)
Automatic tape slack canceller
Cassette compartment illumination
Standby mechanism with unattended recording
Output level controls with click stop for reference
playback level
CT-F8ss50
Power Requirements .............-. AC 120V 60Hz
Power Consumption ...........--02000% 50 watts
Dimensions ....... 420(W) x 150(H)} x 361(D) mm Max.
16-9/16 x 5-15/16 x 14-1/4 in.
Weight .......... 0.02. 9.2kg (20 Ib 4 oz.)
Furnished parts.......... Stereo connecting cords with
pin plugs x2
Head cleaning swabs x 3
Operating instructions x 1
NOTE:
Specifications and the design subject to possible modifi-
cation without notice due to improvements.
NOTES:
1. Reference Tapes: Standard & LH: DIN 45513/BLATTE6 or
equiv.
: CrO,: DIN 45513/BLATT7(CrO, ) or equiv.
. Reference Recording Level: Meter OdB indicating level (160
nwb/m magnetic level = Philips cassette reference level)
. Reference Signal: 333Hz
. Wow & Flutter: e JIS [3kHz, with acoustic compensation
(weighted), rms value]
5. Frequency Response: @ Measured at —20dB level, DOLBY
NR OFF, level deviation is $6dB without indication.
6. Signal to Noise Ratio: @ Measured at the third harmonic distor-
tion 3% level, weighted. e
7. Sensitivity: Input level (mV) required for reference recording
level with input (REC) controls set to maximum.
8. Maximum Allowable Input: While decreasing settings of input
(REC) tevel controls and increasing level at input jacks, this is
the maximum input level (mV) at the point where recording
amplifier output waveform becomes clipped.
9. Reference Output Level: Playback output level when meter
indicates OdB.
10. Maximum Output Level: Playback output level with respect to
reference recording level when output (PLAY) level controls
are set to maximum.
N
Ww
Unit mm

2. FRONT PANEL FACILIES
Cassette compartment illumination
Pe ens
fp neenfemnn |
SENOUST COM
CLOSED LGOP DUAL CaPSTAN
2-MOTOR Tap
(POWER SWITCH
The
power
comes
on
when
the
POWER
switch
is
depressed.
The
level
meter
and
the
cassette
compartment
illumination
will
then
come
on.
@ DUST COVER
When
you
are
not
using
the
deck,
always
keep
this
cover
in
place
to
prevent
dust
and
dirt
from
adhering
to
the
head
section
and
rotating
parts.
(@ REMAINING TAPE MARKER
If
this
marker
is
visible,
it
means
that
there
is
enough
tape
remain-
ing
for
several
minutes
of
recording
or
playback
@TAPE COUNTER
This indicates the position of the tape run.
(5) TAPE COUNTER RESET BUTTON
Depress this button to reset the tape counter display to “000.”
(MONITOR SWITCH
This switch is used to:select the output signals including those of
the
headphones.
The
level
meter
display
is
also
selected
simulta-
neously and so when adjusting the recording level, be sure to set
this switch to SOURCE (depressed position).
For recording: If you depress this switch to SOURCE, you will
be able to listen to the signals (recording input)
just before they are recorded. If you then release
to switch to TAPE, you will be able to hear
the signals immediately after they have been
recorded (playback sound).
Select this switch while you are recording
(alternately between TAPE and SOU RCE) and
monitor the recording.
Release the switch to TAPE. You will not be able
to listen to the playback sound if the switch is set
to SOURCE.
For playback:
©® © © ® @
@METER SELECTOR SWITCH
PEAK: When this switch is depressed to PEAK, the meter
functions as a peak meter.
AVERAGE: When the switch is released to AVERAGE, the
meter functions as an ordinary level meter.
(DOLBY NR SWITCH
Set this switch to ON for recording with the built-in Dolby noise
reduction system and for the playback of tapes which have been
recorded using the Dolby NR system.
@TAPE SELECTOR
This selector allows the bias and equalizer characteristics to be
selected during recording and the equalizer characteristics during
playback in line with the type of tape you are using.
METAL: For using metal tapes
STD: For using ordinary or LH tapes
CcrO : For using chrome tapes
Fe-Cr: For using ferrichrome tapes
(BIAS CONTROL
Use this control to adjust the bias in accordance with the
characteristics of the tape being used. It is set so that the center
(click stop) position corresponds to the standard bias.

CLOSED LON DUAL CaPsTans
@-MOTOR TAPE TRANSPORT SYSTEM
()METALTAPE INDICATOR
This light comes on when the TAPE selector is set to METAL.
(DOLBY NR INDICATOR
This
lights
up
when
the
DOLBY
NR
switch
is
set
to
ON
and
it
indicates
that
a
tape
is
being
recorded
or
played back
with
the
Dolby
NR
system.
(3LEVEL METERS
These
indicate
the
input
level
during
recording
and
the
output
level during playback.
By
operating
the
METER
selector
switch,
it
can
be
made
to
func-
tion as a peak meter, or as a level meter.
The
input
signal
level
is
indicated
when
the
MONITOR
switch
has
been
depressed,
and
the
playback
output
level
is
indicated
when
the
MONITOR
switch
has
been
released.
(INPUT (RECORDING LEVEL) CONTROLS
Use these to adjust the level of the input signals from the MIC
jacks or rear panel INPUT.
Turning
these
controls
to
the
right
increases
the
level.
The controls are coupled to the left and right channels, but you
can
also
use
them
to
adjust
the
right
channel
(back)
and
the
left
channel (front) independently.
(5 OUTPUT (PLAYBACK LEVEL) CONTROLS
Use these to adjust the output signal level during playback.
Turning the controls to the right increases the level. The controls
are coupled when turned but it is also possible to adjust the right
channel (back) and the left channel (front) independently.
When playing back a reference tape (160 nwb/m), a reference
playback level (0dB) is obtained with these controls set to the “6”
click stop position.
(MIC JACKS
These are the input jacks for microphone recording. Plug the left
channel microphone into the L jack and the right channel micro-
phone.into the R jack.
CT-F8S8s50
. SDOROOSsEeRsIe mee
08 -20 -"0-7-5-2 0 43-88
Se tt) ly
()HEADPHONES JACK
This
is
the
output
jack
for
your
stereo
headphones.
You
will
be
able
to
hear
sound
from
signals
selected
by
the
MONITOR
switch.
Use
this
jack
when
you
want
to
monitor
the
quality
of
a
recording
or
when
you
want
to
listen
to
a
tape
privately
on
the
CT-F850.
NOTES:
@
Use
low-impedance
headphones.
If
you
use
a
high-impedance
model,
you
will
not
be able
to
obtain
sufficient
volume.
@
You
will
damage
the
microphone
if
you
plug
-it
into
the
PHONES
jack
by
mistake.
@SOPERATING SWITCHES
#4 (REW): Depress this switch to rewind the tape at high
speed. (The tape will travel from right to left.)
be (FF): Depress this switch to send the tape forward at
high speed. (The tape will travel from left to right.)
m@ (STOP): Depress this switch to stop the tape run and to
release the operating switches.
> (PLAY): Depress this switch when playing back a tape. (The
tape will travel from left to right.)
REC: Depress this switch together with the » (PLAY)
switch for recording.
This switch will not work when a cassette is not
loaded or when the erasure prevention tabs of a
loaded cassette have been broken off.
PAUSE: Depress this switch to stop the tape temporarily
during recording or playback. Depress it again to
allow the tape to continue to travel as before.
NOTES:
@ When any of the operating switches are depressed, the cor-
responding indicator (except STOP mode) will come on
signifying that the deck is set to that respective mode.
e@ The operating switches will not return to their original posi-
tions even when the power is switched OFF.
* Manufactured under license from Dolby Laboratories.
* Dolby and [XQ] are trademarks of Dolby Laboratories.

3. LEVEL DIAGRAM
PLAYBACK
DOLBY
PB
AMP
AMP:
TAPE
@
$2
(MONITOR)
LINE
OUT
FLAT AMP GuzpuT
LEVEL
a ad PS LEVEL CONTROL
ADJ.
@ HEADPHONES
+5.1dBV
0
G) - 3dav
(0708v) LO-S:4d8v} @ - 7aBv
~10
(0.48V)
—(o.447Vv)
RL:50kN.
RL: 82
ee
©
-
22.7
48v
~
>
a
(56.23
mv)
(70.79mv)
(73.3
mv)
= -30
= @ -36dav
aed (15.85 mv )
a -40
>
twa
a
i
a °
-60
O dBV : IV
FREQUENCY: 333 Hz
~70 T@ -74aBv
{0.20mvV )
-80

CT-F850
RECORDING
LINE DOLBY REC BIAS
AMP. AMP. AMP. TRAP
LINE IN
REC
LEVEL
HEAD
CONTROL
INPUT
LEVEL
a
MIC
CONTROL
AMP.
(MONITOR)
osc
,
@
-3
48v
—-—_
©
-3
d8v
©®
-10d8v
(0.708v)
|@
-s8¢av
|
(a708v)
sto
Si
(0.398V)
dicta
dee
@
-18.74BVv
ERT
-20
O.lleV)
=
VR
MAX.
7.58mv
i
>
bseou=-
1@
-27308v
|@
aoetov
@-26a8}v
a
©
-28.5
d8v
a
24.5dBV
yo
;
(50.12
mV)
-—
301
(59.57mv)
if
(43-15m¥)
aes
-4
1.86mV)
|
<
=
7
AV
RMANG
Mince
ees
©
-4348v
w
H
VR
MAX
(708
mv)
4
-50
-~43d8V
ae:
{]
-60
(osomv)
!
FREQUENCY:
333Hz
-70
3
-71.9dBV
(0.25
mv)
-80 vr max:

4. DISASSEMBLY
EXTERNAL COMPONENTS
1. Undo screws 1—4 to remove the bonnet.
2. Undo screws 5—10 to remove the front panel.
38. Undo screws 11—18 and remove washer 19 to
remove the base plate.
Fig.
4-1
Disassembly
of
externa!
part

CT-F3s50
FLUORESCENT DISPLAY TUBES
Undo the single screw to remove the display
assembly. The fluorescent display tubes are
mounted inside the display assembly, and will
require the use of a soldering iron for removal.
This step must be: performed carefully in order to
prevent damage to component parts.
MECHANICAL ASSEMBLY
Once the front panel has been removed, undo
screws 1—6.
Mechanical
Indicator amp
assembly
assembly
Fig. 4-3 Removing the fluorescent display tubes
Fig. 4-2 Removing the mechanical assembly
Sub-Head
Base
Ass’y,
Pinch
Roller
Arm
Ass’y
and
4.
Pressure
Arm.
To remove the pressure arm, simply remove E
washer 2. When a pinch roller pressure spring
1.
Undo
screws
1
and
2
and
the
hexagonal
socket
is
to
be
replaced,
take
special
note
of
the
head
bolt
to
remove
the
sub-head
base
assem-
original
spring
position.
It
will
also
be
neces-
bly.
sary
to
readjust
spring
pressure
in
accordance
2.
Undo
the
height
adjuster
nut
to
remove
the
to
the
requirements
specified
under
the
section
pinch
roller
arm
assembly
on
the
supply
reel
on
‘Pinch
roller
pressure
adjustment’?
on
side.
page
25.
3. Then remove E washer 1 to remove the pinch
roller arm assembly on the take-up reel side.
SS
5
Height adjuster
Pinch roller arm assembly
(supply reel)
Hexagonal socket head bolt
Sub-head base assembly
Pinch roller arm assembly
(take-up reel)
Fig. 4-4 Removing the sub-head base ass’y, pinch roller arm ass’y and
Pressure arm

MECHANICAL ASSEMBLY COMPONENT
PARTS 3. Undo screws 6—10 to remove the plunger chas-
When the motor belt needs to be replaced, take sis assembly.
special
note
of
the
order
in
which
component
4.
Undo
screws
11—16
to
remove
the
sub-chassis
parts are disassembled and reassembled. assembly.
1.
Remove
the
capstan
motor
by
undoing
screws
5.
Then
remove
the
take-up
reel
motor
by
un-
2.
10 ¢
1—3 and washers 1—3.
Solenoid A is removed by undoing screws 4
Screws
Take-up
reel motor
Capstan
Flywheel tieror
Fig.4-5. Removing mechanical assembly component parts
doing screws 17 and 18, and washers 5 and 6.
Solenoid B is removed by undoing screws 19
and 20.

5. PARTS LOCATION
FRONT PANEL VIEW
Knob (BIAS VR)
RAA-233
Push Knob
RAC-100
Knob
(COUNTER)
REC
VR
knob
(R)
assembly
RAC-103
RAA-305
Front
panel
REC
VR
knob
(L)
assembly
RAH-299
RAA-303
P.B.
VR
knob
(R)
assembly
RAA-311
Knob
(POWER
SWITCH)
RAC-094
P.B. VR knob (L) assembly
RAA-309
Tape selector knob assembly
Head cover assembly
RAA-307
RXB-209
Knob (B) Knob (A)
RAC-112 RAC-111
FRONT VIEW WITH PANEL REMOVED
Indicator escutcheon
RNK-787
Counter
RAW-126
Volume (VR1, 2)
Take-up reel base assembly (B)
RCV-061
RXB-189
Supply reei base assembly (B)
RXB-191
Switch assembly
Power switch
RSA-021
MIC jack
Sub-head base assembly
RKN-055
RXB-240
Function
switch
Headphone
jack
RSG-071
RKN-056
41
CT-F8s50
TOP VIEW WITH BONNET REMOVED
Indicator amplifier assembly
Take-up motor
RXM-047
Capstan motor
RXM-050
Power supply &
control assembly
RWR-076
Mother assembly Fuse Assembly
RWX-302
REAR PANEL VIEW
Bonnet case
RNA-377
Strain relief
REC-272
4P mount pin jack Power cord
RKB-014 RDG-022
12

6. BLOCK DIAGRAM
+B
+
METER AMP
FLAT
DOLBY
40)
LINE
OUT
-—-+—
+
MEERA
AMP NR AMP |
FRAME ee teeter ae HEADPHONE AMF A" I
\
bot
|
a
BS
DRIVER
a
u
|
7A
le
I
p-|
TAPE
I
!
HEADPHONE,
O10
LEVEL
METER
HEAD
Q)
i
!
&
|
$4-t
5
1
i
,
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|
|
!
!
iN
|
1
ON
O7
source
1
1
|
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Lo
yoroz | T° Coase ! LAY TI
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Le
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—
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O
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AVERAGE
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a
Qio!
PB.
RCH
Te
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ee
ae
a;
q
$3-I
7 LEVEL
CONTROL LINE
MUTING ;
7 7
LINE
FLAT
AMP
IN O MIC Din aura we opal MPX_ COL ae ee REC REC AMP ne ees es ee ae oe ee ——/—
INPUT __ nn | 4 sa-6! r T sqa-z tever 7
[x VOLUME [J LY ly ! 1 on CONTROL | 7
MIC
AMP
__LINE
ae
|
1%
%
|
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|
ie
pac
Ave
ine
!
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sees,
CR
eee
|
|
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I | i ei er er DOLBY NR aso I
(Tet
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18
|
5 aneereenee ae eee l ev
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Z
7
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2
.
|
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REC AMP |
7 ” MUTING
| |
PL8O!
]
|
| |
1 |
! i
+B Qs
CONTROL
T,,
AC
120V
CIRCUIT
e
{)
0.S.C.
La,
60Hz
METAL
oe
Ef)
E.H
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Croz 6 a
Fe-Cr S$5-3 ieee: ‘
13

7. CIRCUIT DESCRIPTIONS
7.1. RECORDING AND PLAYBACK CIRCUIT
Playback Equalizer Amplifier
This playback equalizer amplifier is an NFB type
amplifier equipped with low-noise, high gain mono-
lithic IC (AN370).
Playback Flat Amplifier
This flat amplifier consists of a single transistor
Qioz. Recording bias mixing is prevented by a
trap circuit in the input stage.
Headphone Amplifier
The headphone amplifier is incorporated inside
IC301 (PA4001) (Note 1). Gains is approximately
11dB.
Mic Amplifier
The mic amplifier is also incorporated inside
IC301 (Note 1). The input stage contains a dif-
ferential amplifier, while the output stage is an
emitter-follower.
Line Amplifier
The line amplifier is another of the stages
located inside IC301 (Note 1). The input stage of
this flat amplifier is also a differential amplifier,
but the output stage is complementary.
Recording Amplifier
The input stage of this amplifier (also contained
in IC301 (Note 1)) is again a differential amplifier,
and the output stage complementary.
NOTE 1: IC301 (PA4001)
This 16-pin dual line IC has been developed by Pioneer
especially for use in tape decks. It contains the mic, line,
recording, and headphone amplifiers.
Fig. 7-1
Block diagram of the PA4001
7.2 TAPE SELECTOR AND EQUALIZER
Tape Selector
Suitable equalization and bias levels for the type
of tape being used are selected by the front panel
Tape Selector (Ss) (STD, METAL, CrO2 and
Fe-Cr)
C333
1,302 332 6.015
330 1
Sos [ease he
> R:
R: R346;
CT-F850
Playback Equalizer
Playback equalization is 7Ousec for metal,
CrO2 and Fe-Cr tapes, and 120usec for standard
tapes. In the METAL, CrOz, and Fe-Cr positions,
+B is passed via Ss to Qio1, thereby turning the
transistor on. As a result, the time constant is
set to 7Ousec by Rios and Ci1o. In the STD po-
sition, Q101 remains off, thereby setting the time
constant at 120usec. C125 and Riio are employ-
ed to reduce the switching noise generated when
Qio1 is switched.
SS: TAPE SELECTOR
ME
PLAY PB.EQ AMP
HEAD
2ST0
Fig. 7-2. Playback equalizer circuit
Recording Equalizer and Recording Bias
Recording Equalizer (Peaking Circuit)
The peaking characteristics are switched by
the switching action of the tape selector. Peaking
frequency is about 15kHz in the STD position,
about 18kHz in the CrO2 and Fe-Cr positions, and
about 19kHz in the METAL position.
Recording Bias
Suitable recording bias level is also set by the
switching action of the tape selector Ss. The
+B voltage for the oscillator circuit is supplied
by the Qs11 constant voltage circuit. The record-
ing bias for the STD/Fe-Cr positions is increased
by about 150% for the METAL position, and
about 40% for the CrO2 position. The bias adjust-
ment control can vary the bias by up to + 15%.
REC REC AMP
HEAD S
8a
*8
(tao
wg as
62
ow
Ob
:
ae
sf
S5: TAPE SELECTOR
Fig. 7-3 Peaking circuit
15

Tape Slack Canceller Circuit
The presence of any tape slack in cassette
tapes loaded in closed-loop capstan transport
systems prevents the correct loop tension from
being obtained, and results in loss of proper tape-
to-head contact.
This circuit eliminates any tape slack by first
rotating the supply reel in the rewind direction
for a short period when the cassette tape is loaded.
When the power is switched on and a cassette tape
is loaded, the S4 cassette detector switch is turned
on to pass +B from S7 to Re4o, Ce25, and Qe14,
the transistor being turned on for about 1 second
until C625 is fully charged. And while Qe14 is
on, +B is also passed from S11-1 to Sg-2, reel mo-
BRAKE
SOLENOID
tor RM, De17, Re36, and Qe14, thereby turning
RM in the reverse direction to eliminate any tape
slack.
Qe11is
also
turned
on
at
the
same
time
as
Qe614,
resulting
in
+B
being
passed
from
Qe11
to
Qe61i2
via
Re3i.
When
the
Qe13
transistor
is
turned
on,
the
braking
solenoid
is
activated.
Furthermore,
in
order
to
prevent
tape
being
wound
.
off
the
take-up
reel
once
the
tape
slack
has
been
eliminated,
a
signal
from
a
photo-interrupter
is
passed
via
a
waveform
rectifier
and
one
shot
multi
circuit
to
Q624
which
is
subsequently
turned
on.
Qe614
is
consequently
turned
off
to
stop
the
tape
slack
circuit
and
halt
the
reverse
rotation
of
the
RM.
S7 : CASSETTE HALF DETECTOR (OFF)
S8 > PLAY (OFF)
Sll_: FF (OFF)
Si2 > REW (OFF)
Wareform|
rectifier
Fig. 7-4 Tape slack canceller circuit
7.3. LEVEL METERS CIRCUIT
The headphone amplifier output is amplified by
Qio4, and rectified by D102, the DC portion being
applied to the display driver IC (IC701). This IC
contains 12 level display comparators used to drive
the 12 level display segments (Note1). +B is
applied to one side of the comparators to supply
the reference voltage.
The reference voltage applied to each compa-
rator is set in a stepwise sequence, the lowest
voltage being applied to the low level display end.
+8) «IC 701
@ BA65S
oor
(12) Segment
output
O
The DC portion rectified by Dio2z is compared
with each reference voltage, the corresponding
segment being lit up if the reference voltage is ex-
ceeded.
The level meters may be used as normal VU
meters, or as peak meters, depending on the S3
position (for different response characteristics).
NOTE 1:
Pairs of level display segments light up at levels below
OdB.
Driver IC
IC701
(BAG58 )
] 12 segments
Level meters
(fluorescent
display tubes)
Fig. 7-5 Level meter circuit
16

7.4 DOLBY NR CIRCUIT
The CT-F850 features a type B Dolby NR noise
reduction system where noise is reduced in the mid
to high frequency region only to eliminate much of
the inherent tape hiss. The S/N ratio is improved
by 10dB (max.) in the high frequency range (above
5kHz).
The Dolby NR circuit is incorporated in a
Dolby NR processor IC (PA4005) developed by
Pioneer. This IC employs a voltage controlled
variable gain circuit (VCA), rather than a variable
resistance element used in other more conventional
Dolby NR ICs. See Fig. 7-6 for an outline of
this Dolby NR processor.
Operation During Recording Mode
1. The input signal is applied to the buffer ampli-
fier via the MPX filter. This filter eliminates
the FM pilot signal, and also serves as a 85kHz
bias trap, thereby preventing any accidental
system mis-operation.
2. The buffer amplifier output is divided into 2
positions, the main signal being passed on
directly to the adding amplifier, while the sub-
signal is diverted through the side chain ampli-
fier and clipper before being rejoined with the
main signal in the adding amplifier.
3. Besides being passed on to the clipper, the side
chain amplifier output is also applied to the
voltage controlled variable gain circuit and
integrating amplifier to be fed back to the in-
put side again, thereby forming a variable filter
circuit.
4. Furthermore, the side chain output is also
applied to a high-pass filter amplifier and recti-
fier circuit. The rectified signal is then applied
to the voltage controlled variable gain circuit
as a control signal.
MPX filter Buffer amplifier
CT-FsS50
5. When the level of the signal passed through the
high-pass filter amplifier is low, the rectifier DC
voltage will drop to almost “‘0’’. The turnover
frequency of the variable filter will consequent-
ly be at a minimum. Under these conditions,
the adding amplifier output level will be 10dB
higher (for frequencies above 5kHz) than the
main signal input, and the dynamic range will
be contracted.
6. With a time delay being generated between the
signal applied to the voltage controlled variable
gain circuit and the main signal, the clipper will
not be capable of responding to sudden level
changes. No uncontrolled signal will thus be
applied to the adding amplifier.
7. When the level of the signal passed through the
high-pass filter amplifier is high, the rectifier
DC voltage will also be high, resulting in an
increase in the turnover frequency of the vari-
able filter. The sub-signal level will conse-
quently drop to almost ‘‘0”, and there will be
no contraction of the dynamic range.
Operation During Playback Mode
Although each block operates in the same way
as during recording, the adding amplfier becomes
an inversion amplifier (output phase becomes the
inverse of the input phase), resulting in the inver-
sion of the sub-signal phase, and the formation of
reducing type NFB loop.
In Dolby NR B noise reduction systems, con-
traction and expansion occur within the frequency
band determined by the variable filter circuit. But
in order to ensure complete symmetry in these
operations it is necessary to set a reference level for
the operational point. This is called the “Dolby
NR level”, all signals above this level being con-
tracted and expanded accordingly.
Adding amplifier
Integrating
amplifier
_ controlled —
variable gain circuit
Rectifier High-pass filter amplifier
Clipper
Fig. 7-6 Dolby circuit
we

7.5 CONTROL CIRCUITS
PLAY Mode (Fig. 7-7)
' When a cassette tape is loaded into the tape
deck, the cassette half switch S7 is turned on, and
the capstan motor CM commences to rotate. A
tape slack elimination circuit (described later)
takes up any slack present in the tape at this time.
When Ss-1 is switched on by pressing thea PLAY
key, Qe1s and Qeio are both turned on (Qs03 on),
and the +B current flows via the pinch solenoid,
Qe1is, Dezo and Qe16 to activate the solenoid. The
pinch roller will consequently press against the
capstan resulting in the start of play mode.
At the same time, +B also flows via the Si11,
Ss-2, RM (reel motor), De21, Rea, and Qe16 route
to start the take-up reel turning.
REC Mode (Fig. 7-7)
When the PLAY and REC keys are both pressed,
Ss and So are switched on. The actions of the
pinch solenoid and RM at this time are the same as
described above under PLAY mode.
When the accidental erasure prevention switch
S14 is set to the NO HOLE position because of the
intact erasure prevention tab on the cassette half,
+B flows via the Rs29, Rs30, S9-2, Ss-1 ,Qs03 route,
resulting in Qsoe being tuned on. +B will subse-
quently be applied to Qsoi1 via Qsoe and Rsoe, re-
sulting in the transistor being turned on, and the
oscillator circuit being activated. At the same time
+B will also flow through So-1, Rs31, and LED3,
resulting in the REC indicator lamp (LEDs) being
lit up.
If, however, the accidental erasure prevention
tab has been broken off, S14 will be switched to
the HOLE position, thereby preventing the flow of
+B current to the oscillator. It will consequently
not be possible to commence recording mode.
FF and REW Modes (Fig. 7-10)
When the FF key is pressed to switch S11 on,
+B
will
be
applied
to
Qe12
via
Re3z
and
Re33.
Qei2
and Qe13 will both be turned on as a result.
And with Qei3 thus turned on, +B will flow
through the brake solenoid, Re3s, and Qe13 route
to turn the solenoid off. Since +B also flows via
Sitt, RM, and Si12 to ground, the RM will com-
mence to rotate at FF speed.
The sequence of events is much the same during
REW mode, the difference being the voltage of
opposite polarity applied to RM when Siz is
switched on.
Pause Operation (Fig. 7-7)
During
both
PLAY
and
REC
modes,
+B
flows
via
the
Rea1,
Reaz,
Si0-2,
Ss-1;
and
Qso3
route,
resulting
in
both
Qeis
and
Qei6
being
turned
on,
and
the
pinch
roller
being
activated
(refer
to
PLAY
mode
for
further
details).
If
the
PAUSE
key
is
then
pressed
to
switch
Sio
on,
this
route
will
be
cut,
and
both
Qe1s
and
Qeie
will
turn
off.
The
pinch
solenoid
will
thus
be
switched
off,
bringing
either
the
PLAY
or
REC
mode
to
a
stop.
Auto Start Circuit (Fig. 7-7)
When
the
power
switch
is
first
pushed
on,
PLAY
and
REC
modes
are
inhibited
for
the
few
moments
to‘let
the
power
supply
voltage
stabilize.
At
the
same
time
that
the
power
switch
is
turn-
ed
on,
+B
flows
through
Csis
and
Rsis
to
turn
Qso2
on
and
Qso3
off.
But
when
Csis
is
complete-
ly
charged
up
(about
1
second
later),
Qso2
will
be
turned
off,
and
Qso3
turned
on.
The
tape
deck
will
thus
be
ready
for
operation
in
any
mode.
Direct Switching Timing Circuit
If
the
PLAY
key
was
pressed
during
either
FF
or REW modes, undue tape slack or tape tension
S, PLAY OFF
S, REC OFF
S,,.PAUSE OFF
S,,FF OFF
$,,REW OFF
S,, Accidental erasure prevention
HOLE (detector)
Fig. 7-7 Pause, auto-start and timing circuit
18

will be generated, resulting in mechanical mis-
operation and other accidents. In order to over-
come this problem, fixed stop intervals are employ-
ed during switching operations.
Direct Switching from FF/REW Modes to PLAY
Mode (Fig. 7-7)
During FF mode, +B flows through the Rs11,
Rsi2, and Qso2 route, turning Qsoz on, and Qso3
off. If the PLAY key is then pressed, Ss will be
switched on, and +B will flow via the Rs11,S12-1,
S112 route, turning Qso2 off. +B will subsequently
commence to flow’ through Rsio and Rs14 to
charge up Cs17. During the 0.6 seconds required
to charge up this capacitor, Qso3 will remain off.
Once the capacitor has been fully charged, how-
ever, +B will flow via Rs10 and Rs13 to Qs03 which
will consequently be turned on. And once this
transistor has been turned on, +B will flow via
Resi, Reaz, Sio-2, Ss-1, and Qs03, turning Qeis
and Q616 on to activate the pinch solenoid, and
commence PLAY mode.
Direct Switching from PLAY Mode to FF/REW
Modes (Fig. 7-10)
During PLAY mode, +B flows via Resz, Dsos,
Si2-1,and Si1-2, and Qei2 and Qe:3 are off. If the
FF or REW key is then pressed, S11 or Si2 will be
switched on, resulting in +B being passed via Re32
and Re37 to charge up Ce24.
Once this capacitor has been fully charged (in
about 0.2 seconds), +B is applied to Qe12 via Re32
and Re33 to turn the transistor on. The brake
solenoid is consequently withdrawn to commence
FF or REW mode.
Auto Stop Circuit (Fig. 7-8)
When tape transport stops, this circuit disen-
gages the transport mechanism automatically by
means of a reset solenoid. The tape transport
detector employs a photo-interruptor featuring a
©
13Vv
Photo interrupter at
rT
<4
CT-Fsso
multi-blade device coupled by belt to the take-up
reel, and whose rotating blases interrupt a light
beam intermittently.
During tape transport, the rotating blades of the
photo-interrupter result in the generation of pulse
signals which turn Qéo7 on and off repeatedly, and
likewise charge up and discharge the Ce20 capa-
citor.
Once tape transport stops, the signals from the
photo-interrupter cease, and the Q6o7 continuous
switching action stops. C620 will thus be charged
by +B via Rei9 and Reo.
The base potential of Qeos will consequently
increase, resulting in this transistor being turned
off. The +B current will subsequently flow via
Reo2s, Ce22, Re23, and Re21, with Qeoo and Qe1o
being turned on until the Ce22 capacitor is fully
charged (about 0.2 to 0.3 seconds).
With Qe610 turned on, the reset solenoid is acti-
vated, returning (resetting) the transport mecha-
nism to the STOP mode. All depressed transport
mode keys will also be released at this time.
Switching Circuit for Pinch Solenoid (Fig. 7-9)
At the commencement of PLAY mode, a
momentarily high voltage is applied to the pinch
solenoid (for about 0.5 seconds) in order to supply
sufficient pulling power. But once the solenoid has
been activated, the applied voltage is reduced in
order to avoid overheating the solenoid coil. This
operation is achieved by the Qe17/Qeis saturation
switching circuit.
When the PLAY key is pressed and Ss switched
on Qe1s and Qei6 are turned on, and +B is applied
to Qe17 via Reaz and Coe28, Qei7 remaining on
until Ce2s is fully charged up.
While Qe17 is on, Qe6is is turned on by +B flow-
ing via Reas and Qe17. Resa will thus be shorted
out, and a voltage equal in level to +B will be ap-
plied to the pinch solenoid. Once Cezs is fully
Fig.7-8 Auto-stop circuit
19

charged (in about 0.5 seconds) Qe617 and Qe1s
will be turned off, and Reas will reduce the voltage
being applied to the pinch solenoid.
Ss PLAY OFF
qs03 S8-!
(turned on)
Fig. 7-9 Pinch solenoid circuit
Tape Slack Canceller Circuit (Fig. 7-10)
If there is any slack in the tape loaded in closed-
loop capstan tape decks, it will not be possible to
obtain normal tape tension, nor proper tape-to-
head contact. This circuit causes the supply reel
to be rotated in the reverse direction when a cas-
sette half is loaded, thereby taking up slack present
in the tape.
After the power switch has been turned on, and
a cassette half inserted, the cassette half detector
switch S7 is switched on. +B will flow via S7,
Re4o, Ce2zs, and Qei4, the transistor remaining on
until the capacitor has been fully charged up (ap-
prox. 0.7 seconds).
While Qei¢ is on, +B will flow via the S11-1, Ss-2,
Si2-2,reel motor (RM), Rese, Dei7, Qei4 route,
thereby causing the reel motor to rotate in the
REW direction, and taking up slack in the tape.
At the same time that Qe14 is turned on, Qe11 is
also turned on, resulting in +B being applied to
Qei2 via Qe11 and Re31. Qeiz2 and Qe13 will thus
both turn on, and activate the brake solenoid.
+B O
7.6 MUTING CIRCUITS
Muting When POWER Switch Turned On
This muting circuit eliminates the click noise
normally present when the POWER switch is first
turned on.
When the POWER switch is first turned on, +B
current flows via Cei7 and Re1o to Qeos, turning
this transistor on until the capacitor has been fully .
charged up (approx. 4 seconds). While Qeos is
on, Qeo is also turned on. Consequently, +B
will flow along the De11, Qeo6, Riss, Qio3 route,
thereby muting the LINE OUTPUT. And due to
+B also flowing along the Dsis, R334, Q310 route,
the REC amplifier will also be muted.
Once Ce17 is fully charged, Qeos will be turned
off, resulting in Q606, Qi03, and Q3:i0 also being
turned off. The LINE OUTPUT and REC ampli-
fier will thus be released from the muting action.
Muting When POWER Switch Off
When the POWER switch is turned off, the +B
current decreases at a relatively slow rate. Cei6,
however, is designed to discharge via Resa at a
faster rate, resulting in a current flowing via the
base of Qe6oe and Deio, and Qeos thereby being
turned on.
Cei7 will therefore discharge via 2 routes: Qeoe,
R138, Qi03, and Dsis, R334, Q310, thereby muting
both the LINE OUTPUT and the REC amplifier.
Muting During FF and REW Modes
This circuit is designed to eliminate motor
noise during FF and REW modes, and any other
unwanted noise after the motor has been stopped.
During FF and REW modes, +B is applied to
Qsos via Rs22 and R521, turning the transistor on,
which in turn results in Qsoa being turned on. +B
current will consequently flow through the Dsoe,
Qs04, MONITOR switch S23, Dsie, Riss, Qio3
route to mute the LINE OUTPUT. At the same
S, Cassette half detector OFF
S, PLAY OFF
S,, FF OFF
S,,REW OFF
Fig. 7-10 Tape slack canceller circuit
20

time, +B also flows via Dsi4 and R334 to Q301
to mute the REC amplifier. :
When the MONITOR switch is in the SOURCE
position, only the LINE OUTPUT muting will be
Fig. 7-11
Muting at Start of PLAY and REC Modes
Switching noises generated when the PLAY and
REC keys are pressed are also muted. After the
STOP key is pressed, Qsos, Qs04, Qio3, and Q301
are turned on, thereby muting the LINE OUTPUT
and the REC amplifier.
When the PLAY key is pressed and Ss switched
on, +B flows along the Rs22, Dso9, Sio-2, Ss,
Qso3 route, but Qsos remains on for about 0.6
LINE DUT
removed. Furthermore, +B is also applied to Q301
via the erase prevention switch S14 and the REC
switch S9 to mute the REC amplifier.
REC amplifier
Recording
head
Muting circuit (POWER ON/OFF)
seconds longer while Cs20 is charged up. Once
Qsos is finally turned off, Qsoa and Qio3 will also
be turned off, resulting in the removal of the LINE
OUTPUT muting. But note that because +B will
still flow via the Sia, So-1, Dsi3, R334 route to
Q301, the REC amplifier will remain muted.
During REC mode when the REC key is pressed
and So is switched on, the So-~1 route will be inter-
rupted, thereby removing the REC amplifier
REC AMP
S, MONITOR : TAPE
S, PLAY _—: OFF
S, REC : OFF
S,o PAUSE: OFF
S,,
Accidental
erasure
prevention
ON
(detected)
2503 (turned on except during FF or REW mode)
Fig. 7-12 Muting circuit (FF, REW, REC, PLAY)
21

muting. However, if the accidental erasure pre-
vention tab has been broken off from the cassette
half, +B will still be applied to Q301 via Sia, Dsi2,
R334,
thereby
keeping
the
REC
amplifier
muted.
As
long
as
the
erasure
prevention
tabs
have
been
_
left
intact,
all
the
REC
amplifier
muting
routes
will
be
cut
to
permit
REC
mode
to
proceed.
Muting When REC key Pressed during PLAY
_ Mode
:
When
the
REC
key
is
pressed
after
the
PLAY
_
key
has
already
been
pressed
(Ss
already
switched
on),
the
switch
noise
is
muted
by
the
following
circuit.
When the REC key is pressed and S9 switched
on, +B flows via Rsie, Dsos, Cs22, Rs26, So2z,
-
Sei,
Qso3
route,
keeping
Qso4
on
during
the
pe-
riod (approx. 0.3 seconds) required to fully charge
' Cs22. During this period, +B flows via Dso6 , Qs04,
Dsi4,
R334
to
mute
out
the
REC
amplifier.
At
the
same time, +B also flows via the S23, Dsie, Riss
. route to mute the LINE OUTPUT.
Muting When Switching from REC Mode to PLAY
Mode
Muting is also achieved when the REC key alone
is released during REC mode. When So only is
switched off, thereby switching directly to PLAY
mode, +B is applied to Q301 via S14, S9-1, Ds13
-
and
R334.
The
transistor
is
turned
on
to
mute
out
_ the REC amplifier immediately.
And because +B also flows along the Rsi6,
Dso7, Cs21, Rs2s, Dsi0, So-2, Sei route to Qso3,
Qso4
will
be
turned
on
only
for
the
period
re-
quired to charge up Cs21 (approx. 0.3 seconds),
resulting in the LINE OUTPUT being muted for
this length of time.
When
the
REC
mode
is
stopped
directly
by
re-
leasing
both
the
REC
and
PLAY
keys,
the
REC
amplifier
and
LINE
OUTPUT
are
muted
immedi-
|
ately.
CT-F850
22