SHARP WQ-790 Service Manual

WQ-790W

SERVICE MANUAL

No. S7852WQ790W//

WQ-790W

• In the interests of user-safety the set should be restored to its original
condition and only parts identical to those specified should be used.

CONTENTS

Page

SPECIFICATIONS ...............................................................................................................................................................1

VOLTAGE SELECTION.......................................................................................................................................................2

AC POWER SUPPLY CORD AND PLUG ........................................................................................................................... 2

FITTING OF DIAL POINTER ...............................................................................................................................................2

NAMES OF PARTS ............................................................................................................................................................. 3

DISASSEMBLY....................................................................................................................................................................4

ADJUSTMENT .....................................................................................................................................................................5

NOTES ON SCHEMATIC DIAGRAM .................................................................................................................................. 6

VOLTAGE ............................................................................................................................................................................7

TYPES OF TRANSISTOR AND LED...................................................................................................................................7

SCHEMATIC DIAGRAM / WIRING SIDE OF P.W.BOARD................................................................................................. 8

PARTS GUIDE / EXPLODED VIEW

SPECIFICATIONS

● General

Power source: AC 110-127 V/220-240 V,

50/60 Hz
DC 15 V ["D" size (UM/SUM­1, R20 or HP-2) battery × 10]

Power consumption: 20 W
Output power: PMPO; 120 W (60 W + 60 W)

(AC operation)
MPO (Max.); 30 W
(15 W + 15 W) (AC operation)
RMS; 15 W (7.5 W + 7.5 W)
(DC operation, 10 % T.H.D.)

Speakers: 12 cm (4-3/4") free-edge

speaker × 2
5 cm (2") surround speaker × 2

Input terminal: MIC 1/2; 1 mV/600 ohms

CD/LINE; 350 mV/47 kohms

Output terminal: Headphones; 16-50 ohms

(recommended; 32 ohms)

Dimensions: Width; 630 mm (24-13/16")

Height; 205 mm (8-1/8")
Depth; 215 mm (8-1/2")

Weight: 5.3 kg (11.7 lbs.) without bat-

teries

SHARP CORPORATION

● Radio section

Frequency range: FM; 88 - 108 MHz

SW1; 2.3 - 7.3 MHz
SW2; 7.3 - 22 MHz
MW; 526.5 - 1,606.5 kHz

● Tape recorder section

Frequency response: 60 - 12,000 Hz (Normal tape)
Signal/noise ratio: 40 dB (TAPE 1, recording/playback)

55 dB (TAPE 2, playback)

Wow and flutter: 0.15 % (WRMS)
Motor: DC 15 V electric governor
Bias system: AC bias
Erase system: Magnet erase

Specifications for this model are subject to change without
prior notice.

This document has been published to be used
for after sales service only.
The contents are subject to change without notice.

WQ-790W

FOR A COMPLETE DESCRIPTION OF THE OPERATION OF THIS UNIT, PLEASE REFER
TO THE OPERATION MANUAL.

VOLTAGE SELECTION

Before operating the unit on mains, check the preset voltage. If the voltage is different from your local voltage, adjust the voltage
as follows: Slide the AC power supply socket to the visible indication of the side of your local voltage.

AC POWER SUPPLY CORD AND PLUG

9FF24801830210

9FF24801600292 9FF26802125210

9FF26802125120

FITTING OF DIAL POINTER

1. Remove the main PWB. Attach the dial pointer as shown

A

arrow on the front cabinet, putting it into the section
indicated by arrow .

2. Install the main PWB in the front cabinet and secure it with
the four screws.

3. Turn the tuning control knob in the direction indicated by .
Set the dial pointer to point "0", and then make the rest of
the adjustments.

B

C

Front Cabinet

Dial Pointer (234)

C

Dial Pointer
(234)

"0" Point

A

Tuning Control
Knod (233)

B

Dial Drum (231)

Screw (608)
ø3x10mm

Main PWB

Figure 2

– 2 –

NAMES OF PARTS

WQ-790W

16

17 18 19 20 2122 23 24

25
26
27
28

11.

(TAPE 1) Cassette Compartment

12.

(TAPE 1) Record Button:

13.

(TAPE 1) Play Button:

14.

(TAPE 1) Rewind Button:

15.

(TAPE 1) Fast Forward Button:

16.

(TAPE 1) Stop/Eject Button:

17.

(TAPE 1) Pause Button:

18.

(TAPE 2) Reverse Mode Switch:

19.

(TAPE 2) Play Button:

10.

(TAPE 2) Fast Wind Buttons:

/

11.

(TAPE 2) Stop/Eject Button:

12.

(TAPE 2) Direction Switch:

1

14 15

29
30

31
32

13.

(TAPE 2) Cassette Compartment

14.

Full-Range Speaker

15.

Surround Speaker

16.

Mixing Microphone Sockets

17.

Mixing Microphone Volume
Control

18.

Surround On/Off Switch

19.

Surround Mode Select Switch

20.

Function Selector Switch

21.

Surround Mode Indicators

22.

Band Selector Switch

23.

Tuning Control

24.

Fine Tuning Control

25.

Spectrum Analyzer

26.

FM Stereo Indicator

789101112

65432

33

34 35 36

37 38 39

27.

Power/(TAPE 2) Play Direction
Indicators

28.

Built-in Microphone

29.

Dubbing Speed/Built-in
Microphone/FM Mode Switch

30.

Extra Bass Control: X-BASS

31.

Graphic Equalizer Controls

32.

Volume Control

33.

FM/SW Telescopic Rod Aerial

34.

CD/Line Input Sockets

35.

Headphone Socket

36.

Beat Cancel Switch

37.

Battery Compartment

38.

AC Power Input Socket

39.

AC Voltage Selector

13

– 3 –

WQ-790W

Front Cabinet

(D1)x5
ø3x10mm

(E3)x1
ø2x6mm

(E2)x2
ø3x10mm

Graphic
Equalizer PWB

Volume PWB

Lug Wire

(E1)x1

DISASSEMBLY

Caution on Disassembly

Follow the below-mentioned notes when disassembling
the unit and reassembling it, to keep it safe and ensure
excellent performance:

1. Take cassette tape out of the unit.

2. Be sure to remove the power supply plug from the wall
outlet before starting to disassemble the unit and remove
the batteries from the unit.

3. Take off nylon bands or wire holders where they need
to be removed when disassembling the unit. After
servicing the unit, be sure to rearrange the leads where
they were before disassembling.

4. Take sufficient care on static electricity of integrated
circuits and other circuits when servicing.

STEP REMOVAL PROCEDURE FIGURE

1 Front Cabinet/ 1. Battery Compartment Lid. 4-1

Rear Cabinet ................................. (A1)x1

2. Screw ................... (A2)x1

3. Screw ................... (A3)x8

4. Socket .................. (A4)x1

2 Tape mechanism 1. Screw ................... (B1)x2 4-2

2. Socket .................. (B2)x4

3. Open the cassette holder.

4. Screw ................... (B3)x6

3 Main PWB 1. Knob..................... (C1)x1 4-2

2. Screw ................... (C2)x4

3. Socket .................. (C3)x5

4 Graphic Equalizer 1. Screw ................... (D1)x5 4-3

PWB

5 Volume PWB 1. Knob..................... (E1)x1 4-3

2. Screw ................... (E2)x2

3. Screw ................... (E3)x1

6 Power PWB 1. Screw ................... (F1)x1 4-4

2. Bracket................. (F2)x1

(B1)x1
ø3x20mm

Front Cabinet

(C3)x1

(C2)x4
ø3x10mm

(B2)x1

Open

(B3)x6
ø3x10mm

(C3)x4

Main PWB

Figure 4-2

Casette Holder
(Left/Right)

Open

(B1)x1
ø3x20mm

Tape Mechanism

(C1)x1

(B2)x3

(A2)x1
ø2.6x10mm

(A1)x1

(A3)x8
ø3x20mm

Figure 4-1

(A4)x1

Main PWB

Rear
Cabinet

Front
Cabinet

Figure 4-3

Rear Cabinet

(F2)x1

Power
PWB

Pull

(F1)x1
ø3x10mm

Power
Transformer

Figure 4-4

– 4 –

ADJUSTMENT

WQ-790W

MECHANISM SECTION

• Driving Force Check

Torque Meter

Play: TW-2412 Tape 1: Over 60 g

Specified Value

Tape 2: Over 50 g

• Torque Check

Torque Meter

Play: TW-2111 30 to 60 g.cm 30 to 60 g.cm
Fast forward: TW-2231 80 to 135 g.cm 55 to 120 g.cm
Rewind: TW-2231 80 to 135 g.cm 55 to 120 g.cm

Specified Value

Tape 1 Tape 2

• Head Azimuth

Test Tape

MTT-114 Headphones Socket

Instrument Connection

(Load resistance: 32 ohms)

* Open the cassette holder, and load the test tape directly into

the mechanism. (Do not load the tape into the cassette
holder.)

• Tape Speed (Normal only)

Test Tape

MTT-111 Tape 1,2:VR501 3,000 ± 60 Hz Headphones

Adjustment

Point

Specified

Value

Instrument

Connection

Socket
(Loadresistance:

32 ohms)

DECK SECTION

• Bias Oscillation

• Beat Cancel Switch: A

Adjustment Point Specified value Instrument

T301 100 kHz + 4 kHz Pin 1 of CNS108

Specified Value

Beat Cancel A: 100 ± 4 kHz

B: 94 ± 4 kHz
C: 104 ± 4 kHz

Connection

TUNER SECTION

fL: Low-range frequency
fH: High-renge frequency

• FM IF/RF

Test Stage

IF T201 Input: FM Antenna
Detection T202 Output:Pin 9 of IC202

Band fL: L202 Input: Antenna
Coverage fH: TC202 Output: Headphone Socket
Tracking fL(88.0 MHz): L201 (Load resistance:

Specified Value/

Adjusting

Point

fH(108 MHz): TC201 32 ohms)

• AM IF/RF

Test Stage

IF T203

MW Band fL: L203
Coverage fH: TC203

MW Tracking fL(600 kHz): L206

SW1 Band fL(2.3 MHz): L204
Coverage fH(7.3 MHz): TC204

SW1 fL(2.6 MHz): L207
Tracking fH(6 MHz): TC209

SW2 Band fL(7.3 MHz): L205
Coverage fH(22 MHz): TC205

SW2 fL(8.5 MHz): L208
Tracking fH(19 MHz): TC210

Specified Value/

Adjusting

Point

fH(1,400 kHz):TC207

• VCO Frequency

Adjustment

Point

VR201 76 kHz ± 200 Hz Pin 13, Pin 21 and ground

Specified value Instrument Connection

Note:

After preparing the test circuit shown in Fig. 5, connect the Pin
13, Pin 21 and ground of the IC202 with the test circuit, and
measure the value.

Instrument

Connection

Instrument

Connection

Input: Antenna
Output: Pin 9 of IC202

Input: Antenna

Output: Headphone Socket

(Load resistance
32 ohms)

of IC202

Pin 13 of IC202

– 5 –

Pin 21 of IC202

D

G

10 pF

1M ohm

10K ohm

FET: 2SK212
(or Other 2SK Type FET.)

S

0.1 µF

TO FREQUENCY
COUNTER

Figure 5 VCO FREQUENCY TEST CIRCUIT

WQ-790W

CNS110

T301

BIAS
OSCILLATION

CNS108

1
2
3
4

SW2
TRACKING

FM
TRACKING

FM
DETECTION

fH

fL

VCO

AM IF

VR201

TC210

L208

fH

T203

IC202

2113

fL

19

T202

TC209

FM IF

T201

IC201

L201

TC
201

TC
207

1

L202

TC
202

TC
203

L203

TC204

TC205

L205

L204

fH

FM BAND
COVERAGE

fL
fH

SW1 BAND
COVERAGE

fL

MW BAND

fL

COVERAGE

fL

SW2 BAND
COVERAGE

fH

MW BAND

fH

COVERAGE

MW
TRACKING

SW1
TRACKING

fH

fL

MW

L206

Figure 6 ADJUSTMENT POINTS

NOTES ON SCHEMATIC DIAGRAM

• Resistor:
To differentiate the units of resistors, The symbol as K and
M are used: the symbol K means 1000 ohm and the symbol
M means 1000 kohm and the resistor without any symbol
is an ohm resistor. The resistor designated “Fusible” is a
fuse type resistor.

• Capacitor:
To indicate the unit of capacitor, a symbol P is used: this
symbol P means pico-farad and the unit of the capacitor
without such a symbol is microfarad. As to electrolytic
capacitor, the expression “capacitance/withstand voltage”
is used.
(CH),(RH),(UJ): Temperature compensation
(ML): Mylar type
(S): Styrol type

• The indicated voltage in each section is the one measured
by Digital Multimeter between such a section and the
chassis with no signal given.

• Schematic diagram and Wiring Side of P.W. Board for this
model are subject to change for improvement without prior
notice.

• Parts marked with “ ” ( ) are important for
maintaining the safety of the set. Be sure to replace these
parts with specified ones for maintaining the safety and
performance of the set.

fH

fL

MAIN PWB

SW1

L207

REF. NO. DESCRIPTION

SW201 BAND SELECTOR FM
SW301 BEAT CANCEL C
SW302 RECORD/PLAYBACK PLAYBACK
SW401 SURROUND MODE LIVE

SELECT
SW402 SURROUND ON/OFF OFF
SW403 DUBBING SPEED/ HIGH/FM STEREO

BUILT-IN MICROPHONE/

FM MODE
SW404 FUNCTION SELECTOR TAPE

SW501 TAPE 2 MAIN OFF
SW502 TAPE 1 MAIN OFF
SW503 TAPE 2 PLAY OFF
SW504 TAPE 2 DIRECTION A
SW505 VOLTAGE SELECTOR AC220-240V

POSITION

– 6 –

WQ-790W

CNS110

T301

BIAS
OSCILLATION

CNS108

1
2
3
4

SW2
TRACKING

FM
TRACKING

FM
DETECTION

fH

fL

VCO

AM IF

VR201

TC210

L208

fH

T203

IC202

2113

fL

19

T202

TC209

FM IF

T201

IC201

L201

TC
201

TC
207

1

L202

TC
202

TC
203

L203

TC204

TC205

L205

L204

fH

FM BAND
COVERAGE

fL
fH

SW1 BAND
COVERAGE

fL

MW BAND

fL

COVERAGE

fL

SW2 BAND
COVERAGE

fH

MW BAND

fH

COVERAGE

MW
TRACKING

SW1
TRACKING

fH

fL

MW

L206

Figure 6 ADJUSTMENT POINTS

NOTES ON SCHEMATIC DIAGRAM

• Resistor:
To differentiate the units of resistors, The symbol as K and
M are used: the symbol K means 1000 ohm and the symbol
M means 1000 kohm and the resistor without any symbol
is an ohm resistor. The resistor designated “Fusible” is a
fuse type resistor.

• Capacitor:
To indicate the unit of capacitor, a symbol P is used: this
symbol P means pico-farad and the unit of the capacitor
without such a symbol is microfarad. As to electrolytic
capacitor, the expression “capacitance/withstand voltage”
is used.
(CH),(RH),(UJ): Temperature compensation
(ML): Mylar type
(S): Styrol type

• The indicated voltage in each section is the one measured
by Digital Multimeter between such a section and the
chassis with no signal given.

• Schematic diagram and Wiring Side of P.W. Board for this
model are subject to change for improvement without prior
notice.

• Parts marked with “ ” ( ) are important for
maintaining the safety of the set. Be sure to replace these
parts with specified ones for maintaining the safety and
performance of the set.

fH

fL

MAIN PWB

SW1

L207

REF. NO. DESCRIPTION

SW201 BAND SELECTOR FM
SW301 BEAT CANCEL C
SW302 RECORD/PLAYBACK PLAYBACK
SW401 SURROUND MODE LIVE

SELECT
SW402 SURROUND ON/OFF OFF
SW403 DUBBING SPEED/ HIGH/FM STEREO

BUILT-IN MICROPHONE/

FM MODE
SW404 FUNCTION SELECTOR TAPE

SW501 TAPE 2 MAIN OFF
SW502 TAPE 1 MAIN OFF
SW503 TAPE 2 PLAY OFF
SW504 TAPE 2 DIRECTION A
SW505 VOLTAGE SELECTOR AC220-240V

POSITION

– 6 –