Sanyo mr 939

Page 1

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Stereo Tape Recorder

mom MR-939

SERVICE MANUAL
SANYO ELECTRIC CO., LTD.

INTERNATIONAL DIVISION : SANYO ELECTRIC TRADING CO., LTD.
OSAKA, JAPAN

SPECIFICATIONS

Speed Accuracy
Jpeed Variation
Wow ..................

$39.5 Standard (7-1/2, 3-3/4 or 1-7/8 ips) Gain Balance, CH-CH 2 dB max. difierence (overall record/
1% Max. (Start to end of reel) play)
0.15% Max. 7-1/2 ips (WRMS VaIUe) Frequency Responce

0.20% Max. 3-3/4 ips (WRMS Value) Record-Plsyv---SPEED 1 FREQUENCY c/s
0.30% Max. 1»7/8 ips (WRMS Value) l10011°00300015000t 10000
Rewind/Fast Forward ----- Up to 2min. for 120011. on 7in. reel l l
7-1/2' 1+7 oi- - +3
Sensrtlblty 1 195 _3 _7
Mlerophone Input-u-67 to -73 (Him for standard Rec. 373/4 ips :2 0 # is _
level on meter
AUX Input ............ ~17 to #23 dBm for standard Rec. 1.7/3 ips _ 0 l :2I _ _
level on meter
/ . _ .........
Power Output (10% Dust.) 3 Watts each channel Reel Torque (gr cm) MODE l LEFT I RIGHT
Cross-Talk, I l
Channel to Channeln-Better than 60 dB PLAY } 30-60 100- 150
Bias Frequency SOKC . g17"
Erase Efficiency -At least so (13 W Mfsflfifl 40")
Signal Noise Ration- Better than 38 dB without Weighting F. FOW. l 30-60 500_700
Network
Hum and Noise --------------- 30 mV Max. Volume and Tone Max. Pinch Roller Pressure ..,...900.1300 gr

DISASSEMBLY

7 To Disassemble:
Step 1. Pull ofl' control knobs.
Step 2. Remove nuts of the headphone and microphone jacks.
Step 3. Remove tape speed selector knob.
Step 4. Remove set-screws and pull ofl control lever.
Step 5. Remove head-housing.
Step 6. Remove screws (five) fixing front panel, and remove
paneL
Step 7. Remove screws (two) fixing chassis to top of cabinet.
Step 8. Remove screws (four) fixing chassis to rear of cabinet.

Remove chassis carefully.

To Reassemble:

' .
Reverse disassembly sequence.

For sub-disassembly and sub-reassembly refer to illustrations in
replaceable parts list.

Page 2

MECHANICAL ADJUSTMENTS

Pressure Roller Tension

PRESSURE RULLER TENSlDN

c , l , \ L
ans m\ \. can swing or Pressure

Roller

PYBSSUH Roller

\Tmtslon Lima

Measurement (refer to fig. 2)

Fig. 2

Pressure between the pressure roller and capstan should be
gauged; satisfactory tension is between 900 and 1300 grams. To
take the reading, play the tape then pull the pressure roller
away from capstan until the tape stops and read the tension
gauge. This process should be repeated two or three times.

Adjustment (refer to fig. 2)

Adjust the pressure roller spring. If spring tension is too
weak, tht the spring 1 or 2 turns shorter or hook it to the
next hole.

If spring tension is too strong, stretch the spring throughout
its length.

Winding Torque For Play, Rewind 8: Fast Forward

Prepare an empty reel (1-3/4' hub) with a few turns of

thread and hook a tension gauge (150-450 grams) to its end.

Measurement (refer to fig. 3)

Lelt mt

Mm Heel

Temm Game
to Fuel Forward
m Play rem-1mg

Fig. 3

Tenwn Game 7m, mu

m Fltwrnd Reading

Operated in each mode, Pull the thread in the opposite
direction, and reed the gauge when the reel stops. Repeat each
reading several times. Normal torque should be as lollows:

LEFT REEL RIGHT REEL
FAST
FORWARD 1.0 - 1.2 015 1.1 - 1.5 lbs
REWIND 1.0 - 2.1 lbs 1.4 - 2.1 ozs
PLAY 1.0 - 2.1 ozs 3.5 - 5.3 025
Adjustment
Forward & Playback
U

or incorrect take-up torque.

1. Check the belt and take-up idler for wear and/or dirt.
Change the belt if necessary, cleaning the motor pulley and
take-up idler.

2. If the belt is in good condition check the felt washer for
oil or wear.

3. If the felt washer is in good condition, check the springs.
Bend the springs or change the thickness of the nylon washer
to increase or decrease take-up torque.

Rewind
lnsufiicient rewind torque could be caused by worn belt or

incomplete travel of the rewind roller lever.

Adjust the nut of the action rod so that the rubber rewind
roller firmly presses against the motor pulley.

Tape Padlressure
Set the unit in Play mode. Press the tension gauge against
the top of the tape pad plate. Read the tension gauge at the
moment when the tape pads separate from the heads.
Normal pressure at the top of the tape pads should be 0.74
1.4 025.

Tension Gauge 0. 7* I . A 013.

Erase or

Record Flay Head
-._ /,. Felt Pad

[Pad Piole
/ tor Erase or R,'P Head.

Fig. 4

ADJUSTMENT OF HEAD HIGHT & AZIMUTH

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Fig. 5

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