Sharp RT-31, RT-31H, RT-31HB Service Manual

SHARP

SERVICE

MANUAL $1

OUTSTANDING RECEPTION THE WORLD

OVER

ATM581

067DCK

Photograph of RT-31

H

Notice: You can make use of the item “DISASSEMBLY”,

regardless of the difference in appearance of the set,

whose photographs are all those of Model

RT-31H

(not RT-31 for SEC.)

SPECIFICATIONS

Power source:

Power consumption:
Semi-conductors:

Dimensions: Width;

Height;
Depth;

Weight:
Tape:

Tape speed

:

Wow & flutter:

Frequency response:

Normal tape;

(RT-31

H/HB)

Normal tape;

(RT-31)

AC 11 OV/22OV/24OV,

50160

Hz

(RT-31

H/HB)

AC

12OV,

50/60 Hz (RT-31)

12 wattes (RT-31

H/HB)

10

wattes (RT-31)

7

ICs

(Integrated Circuits)

12 Transistors

9 Diodes
6

LEDs

(Light Emitting Diodes)

430 mm (16-15116”)

1 15.5 mm

(4-9/l

6”)

237 mm

(9-5/l

6”)

3.9 kg (8.6

Ibs)

(RT-31 H/HB)

3.7 kg (8.2

Ibs) (RT-31)

Philips standard compact cassette

tape

4.8 cm/set. (

l-7/8 ips.)

0.19% (DIN 45 500)

0.06%

(W.R.M.S.) (RT-31

H/HB)

0.065% (W.R.M.S.)

(RT-31)

40 - 12,500 Hz (DIN 45 500)

40-ll,OOOHz~3dB

30 - 14,000 Hz

40-12,000Hz+3dB

00

DOLBY

SYSTEM

@

Noise reduction system manufactured under license
from Dolby Laboratories Licensing Corporation.
“Dolby” and the double-D symbol are trademarks of
Dolby Laboratories Licensing Corporation.

RT-31

For SEC)

RT-31

H

(For SEEG, SUK, SCA

and

General)

RT-31

HB For SEW

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

MAXELL

UDXLII

tape;

(RT-31

H/HB)

40-14,000Hz(DIN45500)

40 - 13,000 Hz 2 3

dB

MAXELL

UDXLII

tape;

(RT-31)

30 - 15,000 Hz
40 - 13,009 Hz f 3

dB

TDK Metal tape; 40 - 16,000 Hz (DIN 45 500)

(RT-31 H/HB)

40 - 14,000 Hz f 3

dB

SONY

Fe-Cr

tape; 40 - 14,000 Hz (DIN 45 500)

(RT-31

H/HB)

40 - 13,000 Hz + 3

dB

S/N ratio (MAXELL

UDXLII

tape):

Dolby NR off;

56

dB

Dolby NR on; 66 dB (at over 5

kHz)

Input sensitivity and input impedance:

Microphones;

0.2 mV (6.8K ohms)

Line in;

50 mV (50K ohms)

DIN input;

0.2 mV

(6.8K

ohms) (RT-31 H/HB)

Output level and loaded impedance:

Headphones;

46 mV (“0”

dB)

, 8 ohms

Line out; 550 mV

(“0”

dB), 50K ohms

DIN output; 550 mV

(“0”

dB), 50K ohms

(RT-31 H/HB)

Specifications are subject to change without prior notice.

SHARP CORPORATION

SHARP ELECTRONICS

CORPORATION

DISASSEMBLY

(Photographs of RT-31H)

Prior to the disassembly, be sure to remove the AC supply
cord from a wall outlet and the input/output plugs from the
rear of the set. Take out a cassette tape, if loaded in the
cassette compartment,

=

REMOVAL OF CABINET

(See Figures

2-1

and

Z-2)

From the cabinet, remove four screws two each at its
right and left sides, and one screw at its rear surface.
Then take the cabinet off.

Figure 2-l

n

REMOVAL OF BOTTOM PLATE

(See Figure 2-3)
Turn the set upside down, remove two screws from the
bottom plate, and take the bottom plate off by shifting
it in the arrow direction.

n

REMOVAL OF FRONT PANEL

(See Figures 2-4 and 2-5)

18Remove four screws from the front panel.

2 Push down three stoppers at the upper surface of the

front panel, See that the front panel is now free from
the stoppers.

@

Pull the front panel frontwards.

Figure 2-4

n

REMOVAL OF MECHANISM BLOCK

(See Figures 2-6 and

3-l)

Note:
Be sure to open the cassette compartment lid before

disassembling the mechanism block,
18Remove two screws from the bottom of the set.
2 Remove two screws from the rear of the mechanism

block.

@

Detach the tape counter belt from the tape counter.

4 Remove the record/playback selector switch rod.

8

5 Remove four sockets from the mechanism block P.W.

board. Then separate the mechanism block from the set.

Figure 2-2

Figure 2-3

Figure

2-5

Figure

2-6

-2-

Figure 3-l

Figure 3-2

’

REMOVAL OF FRONT PANEL CHASSIS

(See Figures 3-2 and 3-3)

Pull out two record level control knobs
Remove one nut from the record level control,
Remove two screws.
Remove eight screws.
Remove one screw. Then the front panel chassis can be

separated from the set.

n

REMOVAL OF METER P.W. BOARD

(See Figure 3-3)

@

Push outward six tabs on the meter

P.W.

board holder,

and remove the meter P.W. board.

Figure 3-3

VOLTAGE SELECTION

(Use of RT-31H/HB)

The unit is designed to operate from

IIOV, 22OV,

or

24OV,

AC mains.
Check the voltage selector setting on the rear panel before
connecting with the AC supply cord.
Adjust the voltage selector to match your local AC power

supply.

The voltage selector is located on the rear panel of the unit.

If adjustment is necessary, use a screwdriver in order to turn
the selector in either direction until the correct voltage in the
window next to the adjusting screw.

Figure 3-4

CAUTION

(RT-31

H/HB)

If any one of the nylon bands shown in the Figure 3-5 is

once removed for some reason, be sure to reprise it to the
original place in the same appearance as before.

Figure 3-5

-3-

MECHANICAL

ADJUSTMENT

Pinch Roller Spring

Figure 4-l

n

PINCH ROLLER PRESSURE ADJUSTMENT

(See Figure 4-l and 4-2)

1.

Place the unit in play mode,

2. Use a tension gauge (0 - 500

gr.)

to push it to a part

@

of the pinch roller until the pinch roller comes away
the capstan. Next gradually weaken the force in the
reverse direction until the pinch roller hits the capstan
(that is, it begins rotating), then see that tension gauge
is reading 295 to 365 grams.

3. Make sure there are clearances

6

0

,

@and @

between

the pinch roller lever and sub. chassis.

4. If the above value is not satisfied, adjust the pinch roller
pressure spring by bending it, or replace.

n

TORQUE CHECK AT PLAY, FAST FORWARD AND

REWIND MODES

1. Put a torque measuring cassette into the set.

2. The torque values, in each mode must be as tabulated
below.

n

TAPE SPEED ADJUSTMENT

1. Using a test tape (TEAC, MTT-113C, 8

kHz

record­ed), play it back at the midpoint but not at the running
start or end point.

2. Connect a frequency counter to the line output socket.

rlgure

4-z

3. Use a bladed screwdriver to adjust, through the adjusting
hole at the bottom of motor, the semivariable resistor

so that the frequency counter reads 2975 to 2995 Hz.

TEST

TAPE
MTT-1

PLAYBACK Mode

Frequency Counter

IIIIlll

13c

000

RECORD/

J

PLAYBACK

\

HEAD

Line output socket (SO3 or S04)

Figure 4-3

-

-4-

ELECTRICAL ADJUSTMENT

=

BIAS CURRENT AND BIAS OSCILLATION FREQUEN-

CY ADJUSTMENT OF RECORD AMPLIFIER

(See Figure 5-l) * SW7 is not used for model

RT-31.

I.

Connect VTVM between the test point

TPIOI

(or

TP201)

and ground.

2. Connect the vertical input terminal of oscilloscope to
the VTVM and its horizontal input terminal to CR
oscillator.

3. Apply the signal

105 kHz

from the CR oscillator to the

unit, and push the tape selector switch SW4.

4. Place the unit in record mode and adjust bias oscillation
coil

L303

so that the bias oscillation frequency is

105 kHz,

while watching Lissajous’ figure on the oscillo-

scope.

5. Push tape selector switch

SW6.

6. Adjust semi-variable resistor VR301 (ro VR302) so that
VTVM indicates 70 mV.

7. Make sure the indicated value of VTVM varies according
to each position of tape selector switch as tabulated
below.

n

ERASE VOLTAGE CHECK

(See Figure 5-2)

I.

Connect VTVM between test point

TP301

and

ground.

2. Connect oscilloscope to the output terminal of VTVM,

3. Push the tape selector switch SW6.

4. Place the unit in record mode, then see that VTVM is
value 210

mV.

n

RECORD/PLAYBACK HEAD AZIMUTH ADJUSTMENT

(See Figure 5-3)

1.

Connect VTVM between the test point TP103 (or

TP203) and ground.

2. Push the tape selector switch SW4 and set the Dolby

NR

switch SW3 at off position.

3. Put a test tape (TEAC, MTT-114, IO kHz, 250

pWb/mm,

-10 dB recorded) into the unit and play it.

4. Adjust the head azimuth adjusting screw so that the

indicated value of VTVM reaches the maximum and a

difference in phase becomes as small as possible.

g

PLAYBACK FREQUENCY CHARACTERISTIC CHECK

(See Figure 5-4)

1. Connect VTVM to the line output socket.

2. Push the tape selector switch SW4 and set the Dolby

NR

switch SW3 at off position.

3. Put a test tape (TEAC,

MTT-217G,

12.5

kHz/l

kHz/

40 Hz, 250

pWb/mm,

-10 dB recorded) into the unit

and play it.

4. See that VTVM is showing the deviation of two different

input signals (40

kHz

and 12.5

kHz)

against the 1

kHz

input, as tabulated below.

Posit ion

Switch Indicated value

I

normal

Push SW4

37

mV

Fe -

Cr

CrOs

Push SW7
Push SW5

41

mV

52

mV

Figure

5-I

Figure 5-2

Figure 5-3

Test Tape

With 40 Hz input

Deviation against 1

kHz

input

shown by VTVM

OdBto6dB

I

With 12.5

kHz

input

(

-3 dB to 4

dB

I

-

Figure 5-4

-5-

=

PLAYBACK SENSITIVITY ADJUSTMENT

(See Figure 6-l

)

1. Connect VTVM between test point

TP103

(or TP203)

and ground.

2. Push the tape selector switch SW4 and set the Dolby

NR

switch SW3 at off position.

3. Put a test tape (TEAC, MTT-150,400 Hz, 200

pWb/mm,

recorded) into the unit and play it.

4. Adjust semi-variable resistor

VRlOl

(or VR201) so that

580 mV will be indicated on VTVM.

n

RECORD/PLAYBACK SENSITIVITY ADJUSTMENT

(See Figure 6-2) * SW7 is not used for model RT-31H.

1. Connect VTVM between test point TP103 (or TP203)
and ground.

2. Connect CR oscillator to the line input socket, and
apply the signal of oscillation frequency 400 Hz, output
level -13 dB (0 dB = 1 V) to the unit.

3. Push tape selector switch SW4 and set the Dolby

NR

switch SW3 at off position.

4. Put a normal tape (TEAC, MTT-502, blank) into the
unit, and place it in record mode. Adjust the record
level control VRIOZ (or VR202) so that the reading
of VTVM becomes 390 mV.

5. Playback the normal tape which has been recorded
in the step 4, and adjust the semi-variable resistor

VR103 (or VR203) so that the reading of VTVM be-

comes 410 mV. Repeat the steps 4 and 5 until the
VTVM reading stays in the range from 360 mV to
460

mV.

6. Put a

CrOs

tape (MAXELL, UDXL

II)

into the unit.

7. Push the tape selector switch SW5, and place the unit in
record mode.

8. Playback the

CrOz

tape which has been recorded in the
step 7, and make sure VTVM indicates the reading
within 326 mV to 487 mV.

m

PEAK LEVEL DISPLAY METER SENSITIVITY ADJUST-

MENT

(See Figure 6-3)

1,

Connect VTVM between test point TPI 02 (or

TP202)

and ground.

2. Set the Dolby NR switch SW3 at off position and
input selector switch SW2 at “LINE” position.

3. Connect CR oscillator to the line input socket, and
apply the signal of oscillation frequency 1

kHz,

316

mV

(-10

dB)

to the unit, placing it in record mode.

4. Adjust record level control VR102 (or VR202) so that
VTVM will indicate 580 mV (-4.7 dB).

5. Change the output level of CR oscillator from 316

mV

(-10

dB)

to 305 mV (-10.3

dB),

then adjust the

semivariable resistor VR601 (or VR602) so that the

segments

(LEDs)

up to 0 dB of the peak level display

meter light up.

6. Again change the output level of CR oscillator from
305 mV (-10.3

dB)

to 295 mV (-10.6 dB), then see

that the segments up to -3 dB remain lit.

n

DOLBY NOISE REDUCTION CIRCUIT CHECK

(See Figure 6-4)

1. Connect VTVM between test point TPI 03 (or

TP203)

and ground.

2. Push the tape selector switch SW4, and set the input
selector switch

SW2

at LINE

posi;tion and Dolby NR

switch SW3 at off position.

3. Connect CR oscillator to the line input socket, and

apply the signal of oscillation frequency

100

Hz, output

level -35 dB (0 dB = 1

V),

to the unit.

Figure 6-l

J

9. Put a metal tape (TDK, AC-71 I) into the unit.

10.

Push the tape selector switch SW6, and place the unit

in record mode.

11. Playback the metal tape which has been recorded in the
step

10,

and make sure VTVM indicates the reading

within 326 mV to 487 mV.

12. Put a Fe-Cr tape (SONY, CS-30) into the unit.

13. Push the tape selector switch SW7 and place the unit
in record mode.

14. Playback the Fe-Cr tape which has been recorded

in the step

10,

and make sure VTVM indicates the

reading within 326 mV to 487 mV.

Line l”PYf sccket

so1 or so2

Figure 6-2

Figure 6-3

Frequency

1 kHz 10

kHz

12.5

kHz

Indicated

45.7 to 44.5 to 42.6 to

Value 81

mV

70 mV 68.2 mV

A

Table

1

Frequency

1

kHz

10 kHz

12.5

kHz

Indicated

8.2 to 13.7 to 13.5 to

Value 16.4

mV

24.9 mV 23.4 mV

Table 2

Figure 6-4

-6-

4. Put a normal tape into the unit and place it in record
mode. Adjust the record level control

VRI

02 (or

6. Give the set the

signal

of oscillation frequency 100 Hz,

output level -50 dB (0 dB = 1 Vi, then adjust the record

VR202) so that VTVM

WIII

indicate 32.6

mV.

5. Give the set 1

kHz

signal, 10

kHz

signal and 12.5

kHz

level control VR102 (or VR202) so that VTVM will

indicate 5.8 mV.

signal one after another, then see that VTVM indicates
the reading listed in Table 1.

7. In the same manner as in the step 5 give the set 1

kHz

signal, 10

kHz

signal and 12.5

kHz.

Consequently, make

sure VTVM indicates the reading listed in Table 2.

ALIGNMENT

POINTS

Figure 7-l

VHILA3160//-1 (ICI)

~-fijTJ

FRONT

VIEW

rlgure I--L tuuIvHLtI\I I l;iKLuI I

I

i i

I

I

I f:

Q301,0302

2SCl214C

P70

I

2SA733K

MARKING SIDE

(Specifications or wiring diagrams of this model

L

7

2

I

FILIOI
FI L20

I

NOTES:

0702 2SD794P

~1

are subject to change for improvement without prior notice.)

3

I

4

5

I

6

Figure 9 SCHEMATIC

c