Sony MEGA BASS CFS-720 User manual

SERVICE MANUAL
CFS-720
US Model
Canadian Model
E Model
Model
Name
Using
Similar
CFS-710
Mechanism
Tape
Transport
MF-730PB-78D
Mechanism
Type
MF-710RP-75D
SPECIFICATIONS
AUDIO POWER SPECIFICATIONS
POWER OUTPUT AND TOTAL HARMONIC DISTORTION
With 6 ohms loads, both channels driven from 70 — 15,000 Hz; rated 5 watts per channel
minimum RMS power, with no more than 10% total harmonic distortion in AC operation.
OTHER SPECIFICATIONS
Frequency range FM 87.6 — 108 MHz
AM 530 — 1710 kHz
Antennas FM: Telescopic antenna
AM: Built-in ferrite bar
Recording system 4-track, 2-channel stereo
Frequency response 70 ~— 10,000Hz
Speakers Full-range: 12cm (4°/, inches) dia. x 2
Power outputs (Canadian model)
Full-range speakers: 5W + 5W
(at 10% harmonic distortion) in DC operation
inputs MIX MIC input jack (mono minijack) (1)
sensitivity 3.9mV for low impedance
microphone
CD/LINE IN jack (stereo phono) (2) input
impedance 50 kilohms, sensitivity 0.43V
Outputs Headphones jack (stereo minijack) for
16 — 68 ohm impedance headphones
Power requirements 120V AC, 60 Hz
9V DC, six size D (R20) batteries
Power consumption 22W in AC operation
Battery life
Sony New Super
SUM-1
(NS)
Approx.
5.5
hours
Sony AM1 (N)
Dimensions Approx. 681 x 215 x 225 mm (w/h/d)
(26% x 8'4 x 874 inches)
not incl. projecting parts and controls
Weight Approx. 6.5 kg (14 Ib 5 02) incl. batteries
Accessory supplied AC power cord (1)
Design and specifications subject to change without notice.
RADIO CASSETTE-CORDER
SONY.

CFS-720
TABLE OF CONTENTS
Section Title Page Section Title Page
1. GENERAL 5-2. Printed Wiring Boards ............... cess eee a
1-1. Location and Function of Controls .............. 3 5-3. Schematic Diagram —Tuner Section—.......... 15
5-4. Schematic Diagrams —Audio Section— ........ 19
2. DISASSEMBLY .
2-1. Removal of Cassette Lid Assy ......0...eeeee eee 4 6. EXPLODED VIEWS
| 6-1. Cabinet (Rear), Speaker Section ................ 22
3. MECHANICAL ADJUSTMENTS.................... 5 6-2. Cabinet (Front) Section ...........0.e cece eens 23
6-3. Deck A mechanism Section (1) ................ 24
4. ELECTRICAL ADJUSTMENTS 6-4. Deck A mechanism Section (2) ................ 25
4-1. Tape Recorder Section ............ 0... cece eee 6 6-5. Deck A mechanism Section (3) ................ 26
B20: « ~ RACIO SECLION paket Praia d wendlen de sewed 8 6-6. Deck B mechanism Section (1) ................ 27
6-7. Deck B mechanism Section (2) ..............7. 28
5. DIAGRAMS
5-1. Semiconductor Lead Layouts ...............0 10 7. ELECTRICAL PARTS LIST ...................... 29
SAFETY CHECK-OUT
After correcting the original service problem, 3. Measuring the voltage drop across a resistor by
means of a VOM or battery-operated AC volt-
meter. The “‘limit” indication is 0.75 V, so
analog meters must have an ‘accurate low-
voltage scale. The Simpson 250 and Sanwa
SH-63Trd are examples of a passive VOM that
is suitable. Nearly all battery operated digital
multimeters that have a 2V AC range are
suitable. (See Fig. A)
perform the following safety check before releasing
the set to the customer:
Check the antenna terminals, metal trim, “metallized”
knobs, screws, and all other exposed metal parts for
AC leakage. Check leakage as described below.
LEAKAGE TEST
The AC leakage from any exposed meta! part to
earth ground and from all exposed metal parts to any
exposed metal part having a return to chassis, must
not exceed 0.5mA (500 microampers). Leakage
current can be measured by any one of three
methods.
To Exposed Metal
Parts on Set
1. A commercial leakage tester, such as the
Simpson 229 or RCA WT-540A._ Follow the
manufacturers’ instructions to use these instru-
ments.
AC
voltmeter
ee (0.75 V)
2. A battery-operated AC milliammeter. The Data
Precision 245 digital multimeter is suitable for
this job.
Earth Ground
Fig. A. Using an AC voltmeter to check AC leakage.
SAFETY-RELATED COMPONENT WARNING!!
COMPONENTS IDENTIFIED BY MARK A OR DOTTED
ATTENTION AU COMPOSANT AYANT RAPPORT
A LA SECURITE!
LINE WITH MARK A ON THE SCHEMATIC DIAGRAMS
AND IN THE PARTS LIST ARE CRITICAL TO SAFE
OPERATION. REPLACE THESE COMPONENTS WITH
SONY PARTS WHOSE PART NUMBERS APPEAR AS
SHOWN IN THIS MANUAL OR IN SUPPLEMENTS PUB-
LISHED BY SONY.
LES COMPOSANTS IDENTIFIES PAR UNE MARQUE /\
SUR LES DIAGRAMMES SCHEMATIQUES ET LA LISTE
DES PIECES SONT CRITIQUES POUR LA SECURITE
DE FONCTIONNEMENT. NE REMPLACER CES COM-
POSANTS QUE PAR DES PIECES SONY DONT LES
NUMEROS SONT DONNES DANS CE MANUEL OU
DANS LES SUPPLEMENTS PUBLIES PAR SONY.

| CFS-720
SECTION 1
GENERAL
1-1. LOCATION AND FUNCTION OF CONTROLS
[1] Speaker
Display window
BAND—FM/AM select
MEMORY button
FM STEREO indicator
[6]MEGA BASS, 4 band GRAPHIC EQUALIZER
(400Hz, 1kHz, 4kHz, 10kHz), BALANCE controls
[7] HIGH SPEED DUBBING button
[8] VOLUME control
[9] Tape operation buttons (deck A)
mA STOP/EJECT
> PLAY
44° (rightward fast winding)
>P (leftward fast winding)
il PAUSE
<I> DIR (direction)
PHONES (headphones) jack (stereo minijack)
FM/AM preset tuning buttons
12] TUNING (+/—) buttons
f.3] SENS (sensitivity) (DX/LOCAL) button (rear)
+10 (a number of ten figures) preset tuning button
FUNCTION selector
TAPE/RADIO OFF: for playing back a tape or for
recording from a MIX MIC
(mixing microphone)
DUBBING: for dubbing
RADIO: for listening to or recording a radio program
CD/LINE IN: for listening to or recording an external
source connected to the CD/LINE IN
jacks
16 SPACE SOUND button
1. 7/|CD/LINE IN jacks (rear)
MIX MIC (mixing microphone) jack (minijack) (rear)
FM telescopic antenna
20| SPEAKER terminal
~AC IN (AC power input) socket (rear)
22|OPR/BATT (operation/battery) and REV (reverse),
FWD (forward) indicators
23 DIR (direction) MODE button
24] Tape operation buttous (deck B)
mA STOP/EJECT
e@ REC (recording)
> PLAY
4<q REW (rewind)
pp FF (fast forward)
T | PAUSE

CFS-720
Note: Follow the disassembly procedure in the numerical order given.
2-1. REMOVAL OF CASSETTE LID ASSY
SECTION 2
DISASSEMBLY
[) Push the claws.
B cassette lid assy

CFS-720
SECTION 3
MECHANICAL ADJUSTMENTS
PRECAUTION
1. Clean the following parts with a denatured-alcohol-
moistened swab:
record/playback head pinch roller
erase head rubber belts
capstan idlers
2. Demagnetize the record/playback head with a head
demagnetizer. (Do not bring the head demagnetizer close
to the erase head.)
3. Do not use a magnetized screwdriver for the adjustments.
4. After the adjustments, apply suitable locking compound
to the parts adjusted.
5. The adjustments should be perfomed with the rated
power supply voltage unless otherwise noted.
6. Power supply voltage: 9V dc.
Torque Measurement
(DECK A)
Forward
Reverse
Fast
(DECK B)
Forward
Fast Forward
and CQ-201B
Rewind
Meter reading
28— 65g*cm
(0.39 —0.90 oz*inch)
2.5—5.5g¢cm
(0.035 — 0.076 oz*inch)
28—65g-cm
(0.39—0.90 oz*inch)
2.5—5,5g*cm
(0.035 —0.076 oz*inch)
more than 100g*cm
(more than 1.39 oz*inch)
95—145g-cm
(1.32—2.01 oz+inch)
Meter reading
25—50g°cm
(0.35—-0.69 oz*inch)
2—5g*cm
(0.03 —0.07 oz*inch)
65—110g*cm
(0.90 —1.53 ozeinch)
Tape Tension Measurement
(DECK A)
Meter Reading
more than 120g
(more than 4.23 oz)
(DECK B)
Meter Meter Reading
more than 170g
CQ-4
aes (more than 6.00 oz)
Head Height Adjustment
1. Use CQ-009C (Part No. 8-909-708-01) or prepare an adjust-
ment cassette as shown below.
C-90 Cut out hatched
tape cassette portions.
2. In playback mode and viewing from the front, adjust the
head heights to eliminate tape curl and tape twist at
portions shown by arrows.
DECK A
playback head
e head height adjustment shim
3-578-138-01 0.1
3-578-138-11 0.2
- DECK B
record/ playback head
r
SS 7
[ [Pan Ne [4] 7
3-578-138-01 | 0.1 a
® | 3-578-138-11 | 0.2
3-578-138-21
A
3-331-108-01 | 0
head height adjustment shim

CFS-720
SECTION 4
ELECTRICAL ADJUSTMENTS
4-1. TAPE RECORDER SECTION
e Standard Input Level
Input terminal LINE IN
input signal level 0.44V (—5dB)
e Standard Output Level
Output terminal SP OUT HP OUT
are a6) | 0250 (1088)
e Test Tape
[tweet dCs «|
P-4-A063 6.3kHz, —10dB head azimuth adjustment
WS-48A 3kHz, 0dB tape speed adjustment
@ Switch and Controls Position
GRAPHIC EQUALIZER controls
(RV G31=2335). vate ecndvereoetenaeg we mechanical mid
VOLUME control (RV301) ........ 2... cee eee eee max.
SPACE SOUND switch (S305)...... 0... cece eee eee OFF
Head Azimuth Adjustment
Parform adjustments in both forward and reverse playback
modes for DECK A.
Output level of both forward and reverse playback modes
should match together.
Procedure :
1. Mode: playback
test tape
P-4-A063 VTVM
(6.3kHz, — 10dB)
OTe:
Phones jack
2. Turn the adjustment screw for the maximum output
levels. If these levels do not match. turn the adjustment
screw until both of output levels match together within
2dB.
L-CH
peak
R-CH
peak
sere SS aie
position L-CH R-CH alg
peak peak
3. Phase Check
Mode: playback
test tape
P-4-A063
L-CH 320
oscilloscope
Phones jack R-CH
Screen Pattern
in phase 45° 90° 135° 180°
see — Yeti, seers”
good wrong
Note: Finish the screw adjustment with a turn in the clock-
wise direction.
After the adjustment, apply suitable locking com-
pound to the adjustment screw.
Adjustment Location :
forward reverse
adjustment screws
adjustment screw

Tape Speed Adjustment
Procedure :
© Perform high speed adjustment before normal speed adjust-
ment.
Mode: playback
test tape
WS-48A
(3kHz,
OdB)
frequencny
counter
Phones jack
Test pin Adjustment Frequcency
Speed
(TP101) aed counter
| oRven |
High short 5,685 — 5,715Hz
" RVI
Taf Rven
Normal open es
Frequency difference between the begining and the end of the
tape should be within +1.5%.
2,970 — 3,000Hz
Adjustment Location :
test pin (TP101)
high speed : short
normal speed : open
ih
aly MODE
DECK B
7 ouenntmndmmmmntnenn
: F : NORMAL HIGH
— right side view — SPEED SPEED
RV374, RV373
DECK A
rrr AN,
NORMAL HIGH
SPEED SPEED
RV372, RV371
A C)

4-2. RADIO SECTION
e FM Section
Setting :
BAND—FM/AM selecting button: FM
FM rf signal
generator
telescopic antenna
input terminal
22.5kHz frequency
deviation by 400Hz signal
output level: as low as
possible
-@ AM Section
Setting :
BAND-—FM/AM selecting button: AM
AM rf signal
generator
Put the lead-wire
antenna close to
the set.
30% amplitude
modulation by
400Hz signal
output level : as low as possible
VTVM
(range: 0.5—5V ac)
Phones jack
e@ Repeat the procedures in each adjustment several times,
and the frequency coverage and tracking adjustments
should be finally done by the trimmer capacitors.
@ Remove telescopic antenna in FM section adjustments.
FM FREQUENCY COVERAGE
ADJUSTMENT
reading on
digital
voltmeter
adjustment frequeny
part
indicator
L3 8+0.1V 108MHz
87.5MHz
confirm 4.7540.2V
FM TRACKING ADJUSTMENT
Adjust for a maximum reading on VT VM.
AM IF ADJUSTMENT
Adjust for a maximum reading on VTVM.
AM FREQUENCY COVERAGE
ADJUSTMENT
: reading on
adjustment SS we frequeny
digital ae
part : indicator
voltmeter
1.8+0.1V 530kHz
1710kHz
9.5+0.1V

Adjustment Location : main board
telescopic antenna
input terminal
FM rf signal
generator
.
°
VCO Adjustment
Procedure
RV1
vco
ADJ
us
>»
—
li
S
=o
<x
osteen
4i2w2
ost
Zo KO ™
2
nN}
36
=
=z
=<q
Clsta
beso
ee
TOW
oe
b
NY
NO
=
©
ae)
L2
FM
TRACKING
ADJ
: no modulation
0.1V (100dB)
Modulation
Output level :
Carrier frequency : 98MHz
Adjust RV1 for 76kHz+500Hz reading on the frequency
Connect frequency counter as shown below.
counter.
Tune the set to 983MHz.
1
2.
3
ANTI
TELESCOPIC
ANTENNA
telescopic antenna
input terminal
ADJ
O +
(AM)
digital
voltmeter
voltmeter
s
2
S
1-636 ~223-
aN
es
ence
eee
St
2
ee
a
7
— ong
i
selbed
|
ene
oat
-
ta
i
hl
Me
2
atid
basses
ye
frequency counter
(VCO)

SECTION 5
DIAGRAMS
5-1. SEMICONDUCTOR LEAD LAYOUTS
DTA114ES 2SK105A-30 GL-3PR9
DTC114ES
DTC114YS
long short
° Goo anode cathode
E 2SK514-H
Cc B letter side
DTC114TS
2SA1175-HFE
2SC2785-HFE
2S8C2786-L
28C2787
letter side
RB441QT-77
RD11ES-B1
RD6.8ES-B2
| 1$$119
ef eB cathode
2SA952
anode
| SVC203RA-V
Ecs
28C1815-GR
anode
cathode anode
SVC342L-V
Eces
2SD773-34
anode anode
cathode
EC B U15G
cathode
2SD1408
Ss
anode