Sanyo M7790K User manual

SERVICE MANUAL
STEREO RADIO
CASSETTE RECORDER
Power Source
PG Ss Since tak aieets Salome Meme shal ae aS 120V/210V/240V (50/60Hz)
DG i tein cauistuavedttoameeout une een 10.5V
(UM-2, HP 11, C Cell, Babyzelle, R 14) x7
QOULPUL POWER 5: isis tenons sentcmsans ewes AW x 2 (Max.)
Power Consumption ............cce0eeeees 13W
Current Consumption (at Vol. Min.)
Record mode (with Metal) .............. 260mA
Playback mode ..............ccceee eee e es 210mA
Fast Forward mode ................020065 210mA
Rewind mode ..............cceeeeeeeeeees 210mA
Recording System ............cccceseeeeees AC Bias
Erasing System ...............cceceeeeeeees AC Erasing
TAP@ SPO on. cceccec ces sdenscensenntancece 1-7/8ips. +3%
WOW: Sc FIUTED oSseccau dant semslevs sae velesoutee 0.15%, WRMS
Fast Forward Time ...............c0c0s0ees 130sec. (with C-60)
REWING TIME «2s cicccsesdesevodenveeiconsess 130sec. (with C-60)
Torque
Playback ................... i 30 ~ 65g-cm
Fasthorward) sscoscsssactedinces aie akasaws & 55 ~ 180g-cm
FROWA A Givcscrteccecwisrsjiidiose rnieid stersiersoteeeisniatanceiat « 55 ~ 180g-cm
Erase Ratio (Overall, with Fe2Os) ....... 60dB
Signal to Noise Ratio (with Fe2Oa) ...... 45dB
Channel Separation (with Fe2O3) ....... 45dB
AC33
142 38002
SPECIFICATIONS
—Specifications subject to change without notice.—
Frequency Response (Overall)
FOZ Og sca sresiee ne ceescets cis tates walaethuaresciate 50Hz ~ 13,000Hz
GQ 2. cecies secu eee etaerisen cba Saws 50Hz ~ 14,000Hz
Metale cctscccsatisiemantinne steno eee onion 50Hz ~ 15,000Hz
Crosstalk (with Fe2Os)
MACK TOMMACK cies ad ties ond dasa maces sears 60dB
Harmonic Distortion (K3, with Fe203) .. 3%
Hum & Noise (at Vol. Min.) ................ —65dBs
Input Sensitivity and Impedance
NAICS sesorecians ate srttturcroe BOE nat eal aes arse aerate 0.3mV/3.9kO.
LINEN acnjaedtaticoends deat eimaabaiuciinten 300mV/100k0,
Output Level and Impedance
LINE QUT Sindee, waccus semomnancocaad xiao 550mV/2.2k0,
EXE SPOAKOR basis sssesciore:csarejsieieinierneiieseerccetenere 3,200mV/3.20,
Head Phone sservaeccarsiocnuaseentaondtad 3,900mV/320
Oscillation Frequency .................065 60kHz
Frequency Range
MW ist cteottisher enn sieedoanadeannee saemacia 525 ~ 1,605kHz
SW Karns oeariatrarc nate Saaeneeredt andes 2.3 ~ 7.3MHz
SW) Fisnoteciated tasdoeeantelenaee Sena: 7.3 ~ 23MHz
FAME oe views svastestrataausaions auconnawtnaatesnetens stoaates 88 ~ 108MHz
DIMENtONS wssicsnuieoscertecoens 437(W) x 137(H) x 99(D)mm
Weighti: mccasstae. cerscsctonaccsaecutecaceen 2.5kg ©
WM-9533
JGSE2B

DISASSEMBLY INSTRUCTIONS
GENERAL REMARKS 2. Remove the three connectors (CN2, CN3 and CN6) from the
® Before disassembling the unit, spread a soft rubber mat or a Amplifier P.C.Board and detach the Radio Chassis by lifting
cloth on the workbench to avoid scratches and grease stains. it in the directions of the arrow.
@ Do not spread anything which is likely to cause static
electricity because transistors and ICs may be easily
damaged by it.
e Reassemble the unit, noting the kinds of screws and the
soldering and arrangement of the leads. Refer to “Circuit
Diagram and Exploded Views” for correct assembly.
e Before disassembling the unit, take out the cassette tape
and the batteries.
CABINET BOTTOM REMOVAL pace igese
1. Detach the battery compartment tid and remove the eight
screws (1 ~ 8) fastening the Cabinet Bottom.
3. Reassemble in reverse order.
AMPLIFIER P.C.BOARD REMOVAL
1. Detach the Radio Chassis by following the instructions for it
and remove the four screws (9 ~ 12) fastening the
Amplifier P.C.Board.
2. Pullout the connector CN4 from the Amplifier P.C.Board.
CN4
2. Detach the Cabinet Bottom by lifting it in the direction of the
arrow and pull out the connector of the antenna from the
Radio Tuner P.C.Board.
3. Reassemble in reverse order.
RADIO CHASSIS REMOVAL 3. Detach the Amplifier P.C.Board by lifting it in the direction of
1. After detaching the Cabinet Bottom, pull out the Tuning, the arrow noting the lead wires.
Volume Control, Balance Control, Treble Control, and Bass
Control Knobs from the unit. 4. Reassemble in reverse order.

DISASSEMBLY
INSTRUCTIONS
(continuea)
RADIO TUNER P.C.BOARD REMOVAL
1. Detach the Radio Chassis by following the instructions for it
and fully turn the Tuning Shaft in an arbitrary direction.
2. Remove the three screws (13 ~ 15) fastening the Radio
Tuner P.C.Board.
Then, detach the P.C.Board by lifting it in the direction of the
arrow noting the lead wires.
AMSS Control
P.C.Board
3. Remove the three screws (19 ~ 21) fastening the
Mechanism Chassis and unsolder the two leads (pink and
black) from the Motor.
Radio Tuner P.C.Board
3. Reassemble in reverse order. Mechanism Chassis
NOTE:
* Do not turn the Tuning Shaft before the Radio Tuner
P.C.Board is re-mounted to the unit.
* When the Radio Tuner P.C.Board is mounted, insert the
shaft of the variable capacitor into the hole on the drum.
After that, check to see that correct dial indications are
obtained.
MECHANISM CHASSIS REMOVAL
1. Detach the Radio Chassis by following the instructions for it
and remove the screw (12) fastening the Amplifier
P.C.Board. 4. Detach the Mechanism Chassis by lifting it in the direction of
the arrow noting the lead wires.
2. Remove the three screws (16 ~ 18) fastening AMSS :
Control P.C.Board and detach the P.C.Board. 5. Reassemble in reverse order.
—3-

MECHANICAL ADJUSTMENTS
EQUIPMENT REQUIRED
Cassette-type Torquemeter (100g-cm/160g-cm)
. Power Switch
When one of the select buttons (except for the Pause and
e Round-nose Pliers Stop/Eject buttons) is pressed, this Swich is turned on by
e Plus Screwdriver the Shut-off Lever, so that the Motor starts rotating. The
e APair of Tweezers driving motor rotates the flywheel and the rotational force
e Paintor Glue transfered by the actuate gear makes the mechanism
function.
GENERAL
REMARKS
*
Check
that
the
clearance
of
the
switch
contacts
is
0.3
~
1.
When
a
repair
or
an
adjustment
work
on
the
mechanism
is
0.5mm
with
the
Power
Switch
in
contact
with
Shut-off
performed, remove the Mechanism Chassis from the unit Lever as illustrated.
and supply 12V DC from the constant-voltage regulator to
the
Ext.
Power
Jack
on
the
Amplifier
P.C.Board.
-
Screw
2. Before and after the mechanism adjustment, clean the tape Power Switch
contacting surfaces with a soft cloth soaked in alcohol.
Trouble may occur because of oil and grease stains.
0.3 ~ 0.5mm
The belts must be kept clean while the adjustments are
performed.
3. If the Pinch Roller or Belt has quality deterioration such as
scratches, replace it with a new one.
ee Shut-off Lever
4. When the cassette tape is inserted into the cassette holder, .
the Play button can not be pressed.
If the Mechanism is required to function under this
condition, push the Cassette Lever as illustrated, so that the
Button is released and the mechanism functions normally.
2. Play Mute Switch
This switch is normally closed and it is turned off by the
Slide Base when the Play button is pressed.
* Set the unit in the playback mode and check that the
clearance between the switch contacts is more the
Erase Head 0.25mmas illustrated.
Screw
a
Move.
more than 0.25mm j
Slide Base Be
*
a
Push.
Cassette Lever
[ Play Mute Switch
Press the Pause button and check that the clearance
between the switch and the Slide Base is as illustrated.
5. This Mechanism does not function when power is not The clearance should be less than 0.05mm.
supplied and any one of the buttons is pressed.
When the batteries are almost used up and the Play button is
pressed, the Slide Base stops halfway, making it difficult to
remove the cassette tape from the compartment. To avoid
this, replace the batteries with new ones beforehand.
Screw
Move.
less than 0.05mm {
Position Adjustment of Leaf Switches
This model has the following three leaf switches. Checking and
adjustment for each switch must be conducted in accordance
with each adjustment item.
The unit should be set in the stop mode at each adjustment.
* Power Switch
* Play Mute Switch
* AMSS Switch
Slide Base Piay Mute Switch

MECHANICAL ADJUSTMENTS Ccontinuea)
3. AMSS Switch
This Switch is turned on by the Cue/Review Switch Lever
when the unit is set in the cue or review mode by pressing
the F.FWD or Rewind button in the playback mode. Then, the
AMSS circuit is functioning.
* Set the unit in the stop mode and check that the
clearance between the switch contacts is 0.2 ~ 0.3mm
with the AMSS Swtich in contact with the Cue/Review
Switch Lever as illustrated.
Screw
AMSS Switch
Cue/Review Switch Lever
Switch Adjustment
Loosen the screws fastening each switch and move the
switches to the specified positions if position adjustments are
required.
After the adjustment, tighten the screws and secure the
switches with paint or glue.
TAKE-UP TORQUE
1. Insert a cassette-type torquemeter (100g-cm) into the
cassette compartment and set the unit in the playback
mode. Then, check that the take-up torque is 30 ~ 65g-cm.
Take-up Torque
30 ~ 65g-cm
Cassette-type Torquemeter
2. If not, replace the Friction Assembly with a new one.
F.FWD AND REWIND TORQUES
1. Insert a cassette-type torquemeter (160g-cm) into the
cassette compartment and measure the fast forward and
rewind torque. Check that each torque is 55 ~ 180g-cm.
—5—
Rewind Torque
2 = 55 ~ 180g-cm
Fast Forward Torque
2. If not, replace the Friction Assembly with a new one.
AMSS SOLENOID ADJUSTMENT
AMSS (Automatic Music Select System) detects a silent space
(unrecorded portion) between each music on a musictape and
automatically plays back a desired music from the start.
The unrecorded portion should last for more than approximately
4 seconds.
It may not operate correctly in the following cases:
When the recorded sound is often interrupted as in a speech
tape.
When the silent space does not last long enough (less than 4
seconds).
When there is an appreciable noise in the silent space
between two adjacent programs.
When the unit is placed on a television set, AMSS may not
operaie correctiy due to adverse effect of the TV signal. In
this case, put the unit away from the television set.
If AMSS Solenoid is not correctly positioned, AMSS Switch does
not function correctly, F.FWD or Rewind button is released while
AMSS is working, or a button may not be locked. In this case,
perform the adjustment as follows:
1. Remove the Mechanism Chassis from the unit by following
its removal instructions.
2. Loosen the screw fastening the Solenoid and adjust the
Solenoid by moving it in the direction of the arrow, so that the
Plunger Lever is tightly attached to the two absorption
surfaces of the Solenoid as illustrated.
Screw
Solenoid
Plunger Lever
No Clearance

MECHANICAL ADJUSTMENTS (continuea)
After the adjustment, tighten the screw.
Set the unit in the playback mode and check that AMSS
mechanism functions correctly as follows:
* Check if F.F WD button can be locked by pressing it.
Check if Rewind button can be locked by pressing it.
*
button can not be locked or is soon released.
After the confirmation, secure the screw with paint or glue.
RECORD/PLAYBACK HEAD ADJUSTMENT
After a head has been replaced or disassembled, adjust its
position following the procedures.
NOTE:
A Cassette with the specified pin—head distances marked on it
can be used as a very convenient gauge for the Head Position
Adjustment. (Do not use a worn cassette.)
L__Record/Playback Head
1. Set the unit in playback mode and press the Pause button.
Check that the distance from the Chassis Posts to the
Record/Playback Head is 2.0 ~ 2.1mmas illustrated.
Chassis Post mIaNe: q
Screw Screw
Record/Playback Head
Readjust the solenoid position if either F.FWD or Rewind
2. If necessary, loosen the screws’ fastening the
record/playback head and adjust the head to the specified
position by moving it.
3. After the adjustment, tighten the screws and secure them
with paint or glue.
Then, check that AMSS mechanism functions correctly.
ASO LEVER
The service part of the ASO lever is ;noit cut to avoid deforming,
as illustrated.
When replacing, cut 1.5 ~ 3mm of the part indicated in the
illustration.
ASO Lever
1.5 ~ 3mm
NOTICE ON REASSEMBLY
When reassembling the mechanism, check if the resistance
between the screw fastening the Record/Playback Head and the
Lug attached to the Chassis Plate is less than 30.
When the resistance is more, there will be noise during
recording or playback of the cassette tape.
To Screw Record/Playback
Chassis Plate
Van
Less
than
30
Lug

ELECTRICAL ADJUSTMENTS
EQUIPMENT REQUIRED
VTVM (2 sets)
Frequency Counter
Dummy Load (47kQ)
Audio Signal Generator
Attenuator
Dualtrace Synchroscope
DC Constant-voltage Regulator
Test Tapes
* 3kHz Test Tape (Example: TEAC MTT-111) for Tape
Speed Adjustment
* 10kHz Test Tape (Example: TEAC MTT-114) for Head
Azimuth Adjustment
* 4QOHz Test Tape for Dolby Calibration Level (Example:
TEAC MTT-150) for Playback Sensitivity Adjustment
e Test Tapes for Recording and Playback Operations
* Chromium Dioxide Tape (Example: TDK AC-51 2)
* Metal Tape (Example: TDK AC-711)
e Alignment Tool
Uniess especially specified, set the unit and
measuring instruments as follows:
@ Function Switch ............... ccc cece cece cece een eeeeneneeees LINE
@ Dolby NR Switch ........... 0. ccc c cece cece cece cece eeeeeeeeeeee OFF
e@ Tape Select Switch .............cc ccc cec cece ec enee ee ees NORMAL
@ Beat Cancel SWitch .............cc cece cece ee eeeeeeeeeseeeeeeees 2
@ Volume Control ............cccceceeeeseaceseeeaeeees Minimum (0)
e Audio Signal Generator output................. 1kHz, OdB (1V)
NOTE:
*
The Electrical Adjustment should be performed in the
order as described below.
Supply 12V DC from the constant-voltage regulator to the
Ext. Power Jack.
TAPE SPEED ADJUSTMENT
1. Remove the Radio Chassis from the unit and connect a
frequency counter to the left or right channel LINE OUT as
illustrated. Then, insert a 3kHz test tape (Example: TEAC
MTT-111) into the cassette compartment.
Frequency Counter
Dummy Load 47kQ. LINE OUT
2. Adjust the tape speed by slowly turning the potentiometer
inside the Motor until the frequency counter reads 3,000Hz
(+30Hz).
Potentiometer for Tape Speed Adjustment
HEAD AZIMUTH ADJUSTMENT
1.
Connect a dualtrace synchroscope and a VTVM to both
channel LINE OUT as illustrated.
Then, set the dualtrace synchroscope as follows:
a! | © D | <a ene CHOP (chopped)
* SOURGE. 2.2.25 5ccc.cciacsctcswes INT (internal), CH1 or CH2
* SWEEP MODE................. suai deacce AUTO (automatic)
NOTE:
Adjust the field on the synchroscope with the VOLT. ADJ.
and TIME ADJ.

ELECTRICAL ADJUSTMENTS (continuea)
2. Insert a 10kHz test tape (Example: TEAC MTT-114) into the
cassette compartment. While playing back the test tape, turn
the azimuth adjusting screw until the wave forms of the right
and left channels are superimposed and set to optimum at
maximum reading on the VTVM.
Adjustment
R/P Head
Adjusting Screw
3. After the adjustment, secure the adjusting screw with paint
or glue.
PLAYBACK SENSITIVITY ADJUSTMENT
LEFT CHANNEL
1. Connect a VTVM to the test point TP101 as illustrated and
insert a 400Hz test tape for Dolby Calibration Level
(Example: TEAC MTT-150) into the cassette compartment.
VTVM 580mV
Test Point TP101
2. Check that the VTVM reads 580mV for the output of the left
channel while playing back the test tape.
3. If necessary, adjust the output to the specified one by
turning the potentiometer (P102) while the test tape is
played back.
RIGHT CHANNEL
Connect the VTVM to the test point TP201. Then, adjust the
potentiometer (P202) for the right channel by following the
same procedure as in LEFT CHANNEL.
OSCILLATION FREQUENCY ADJUSTMENT
1. Connect a VTVM across the resistor R104 and a frequecy
counter to the output terminal of the VTVM as illustrated.
Frequency Counter
ii
2.
Insert
a
cassette
tape
into
the
cassette
compartment
and
set
the
OSC
Switch
to
the
position
2.
Then,
set
the
unit
in
the
recording
mode.
3.
Turn
the
core
of
the
oscillation
transformer
(T301)
with
an
alignment
tool
until
the
frequency
counter
reads
60kHz
[
+50Hz].
RECORD & PLAYBACK
FREQUENCY RESPONSE ADJUSTMENT
e Chromium Dioxide Tape
Set the Tape Select Switch to “CrO2” and insert a chromium
dioxide tape (Example: TDK AC-512) into the cassette
compartment. Then, make the adjustment by the following
procedures.
LEFT CHANNEL
1. Connect an audio signal generator and an attenuator to the
left channel LINE IN, and a VTVM to the left channel LINE
OUT as illustrated.

ELECTRICAL
ADJUSTMENTS
(continued)
Audio Signal Generator
1kHz
and
12kHz
Attenuator
31.5mV (—30dB)
LINE IN
Dummy Load 47k
Oy)
LINE_OUT
OUTPUT
1kHz > 1 2kHz, (0.5dB +1dB)
2.
Alternately
record
the
1kHz
and
12kHz
signals
from
the
audio
signal
generator
at
31.5mV
{—-30dB)
on
the
tape
several
times.
3.
Check
that
the
12kHz
signal
output
is
identical
to
the
1kHz
signal
output
or
the
deviation
is
0.5dB
(+1dB)
on
the
VTVM
while
playing
back
the
recorded
signals.
4.
If
necessary,
adjust
the
output
by
turning
the
potentiometer
(P101)
and
re-check
the
output
of
each
signal
by
playing
back
the
signals
after
recording
operation
of
the
signals.
5.
Repeat
the
above
adjustment
until
the
specified
output
is
obtained.
RIGHT CHANNEL
Connect the audio signal generator and the attenuator to the
right channel LINE IN, and the VTVM to the right channel
LINE OUT. Then, adjust the potentiometer (P201) for the
right channel by following the same procedure as in LEFT
CHANNEL.
RECORD & PLAYBACK SENSITIVITY
ADJUSTMENT
e Metal Tape
Set the Tape Select Switch to “METAL” and insert a metal tape
(Example: AC-7 11) into the cassette compartment.
Then, perform the adjustment by the following procedure.
LEFT CHANNEL
1. Connect an audio signal generator and an attenuator to the
left channel LINE IN, and a VTVM to the left channel LINE
OUT as illustrated.
Audio Signal Generator
1kHz
Attenuator
LINE IN
2. Set the unit in the record stand-by mode by pressing the
Pause Button first, and then, the Record and Play Buttons
simultaneously.
3. Feed a 1kHz signal from the audio signal generator into the
unit and adjust the attenuator until the VTVM reads 300mV
(~12dB).
Then, record the signal on the tape by releasing the Pause
Button.
4. While playing back the recorded signal, check that the signal
output is 300mV (—12dB) on the VTVM.
5. If necessary, adjust the potentiometer (P103) and re-check
the reading of the VTVM by playing back the signal after the
recording operation for the signal.
6. Repeat the above adjustment until the specified output is
obtained.
RIGHT CHANNEL
Connect the audio signal generator and the attenuator to the
right channel LINE IN, and the VTVM to the right channel
LINE OUT. Then, adjust the potentiometer (P203) for the
right channel by following the same procedure as in LEFT
CHANNEL.

EQUIPMENT REQUIRED
» AM Standard Signal Generator
FM Standard Signal Generator
Generator Scope
Stereo Signal Generator
Loop Antenna
Ceramic Capacitor (1 OpF)
Carbon Resistor (830kQ)
VTVM
Frequency Counter
NOTE:
Use an alignment tool with plas
MW ALIGNMENT
TUNER ADJUSTMENT
Dummy Antenna (3800/1 OpF) for SW2
Dummy Antenna (75Q, unbalanced type) for FM
tic grip for all adjustments.
Oscilloscope
Dummy Load (3.20)
Alignment Tool
Before performing the adjustment, set the switches and
controls as follows:
* Function Switch ............cccccccccccseccceeeeeeuenes RADIO
* Mode Switch .............c ccc cece eeeeeceneee see eaes MONO
*) “TONE: CONtrOlS: a. s.aascciceseeseeleeesvawiunosisde odtanee’ Max.
* Balance Control ..................... Center (click position)
* Volume Control ............c cece ccees eee eseeeeneeenees Center
Standard Test Frequency 400Hz and Modulation 30% at AM
Frequency
Alignment
Calibration terminal of
1 of IF gene-scope.
for AM
60cm away f
bar antenna.
Calibration
of
Tuning Range | of AM signal
generator.
LU Connections
INPUT OUTPUT
Connect loop
antenna to output
Place loop antenna
Connect loop
antenna tc output
Connect input
terminal of gene-
scope to detector
output terminals
(CN1-1 and CN1-2,
or CN1-3). rom
of Signal
Generator
455kHz
Tuning Dial
Setting Remarks
Adjustments
Obtain symmetrical curve
and maximum amplitude.
Low End T3, T4 and T5
Connect VTVM with
3.20 dummy load
and oscilloscope
Adjustment Place loop antenna | to Phones/Ext.
of 60cm away from Speaker jack.
Tracking bar antenna.
510kHz
1,670kHz
600kHz
pale nne
Obtain sine-wave of 400Hz
and maximum amplitude.
High End
600kHz
1,400kHz
L4-3 (bar ant. coil)
SW1 ALIGNMENT
Alignment
Calibration
of
Tuning Range
of AM signal
generator.
Connect loop
antenna to output
Connections
OUTPUT
Connect VTVM with
3.20 dummy load
and oscilloscope
Adjustment Place loop antenna to Phones/Ext.
of 60cm away from Speaker jack.
Tracking bar antenna.
an
Repeat the above steps until no further change is noted in any of the adjustments.
Frequency
of Signal
Generator
Tuning Dial
Setting
Low End Obtain sine-wave of 400Hz
and maximum amplitude.
High End
2.5MHz
L4-1
(bar
ant.
coil)
Max.
6.5MHz
TC3 (PVC)
Repeat the above steps until no further change is noted in any of the adjustments.