Nakamichi 481, Service Manual

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Page 2: ...1 Switch P C B Ass y 17 3 12 volume P C B Ass y and Control Switch P C B Ass y 17 3 13 Rear Panel Ass y Power Transformer and Power Switch 17 3 14 Cassette Case Ass y and Cover Plate Ass y 19 3 15 Tape CounterAss y 19 3 16 Capstan Motor Ass y and Flywheel Ass y 20 3 17 Sub Mechanism Chassis Ass y 20 3 18 Control Motor Ass y and Reel Motor Ass y 20 3 19 Cam Control volume 20 3 20 Reel Hub Ass y and...

Page 3: ...ntrol Switch Holder Ass y B02 43 9 6 Headphone Jack Ass y B03 43 9 7 Mechanism Ass y 481 B04 44 9 8 Chassis Ass y B05 45 9 9 Flywheel Holder Ass y C01 45 9 10 Sub Mechanism Chassis Ass y C02 46 9 11 Main Mechanism Chassis Ass y C03 47 9 12 Rear Panel Ass y D01 49 9 13 Reel Motor Ass y E01 50 9 14 Control Motor Ass y E02 50 9 15 Head Mount Base Ass y F01 50 9 16 Supply Pressure Roller Ass y F02 50 ...

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Page 5: ...th can now be avoided at changing of cassette tape if only the Record Head azimuth is properly adjusted in advance The Fig 2 1 2 shows trackings of each head against a tape of the N 481 wherein the figure shows ideal locations at the time of designing thus the tracking in actual use will vary more or less depending upon the tape width etc 1 Adjustment of Tape Guide Height Tape Guide of the N 481 i...

Page 6: ...tly generates holdback ten sion As you note if the diameters of the 2 capstans should be the same the generation cycles of wow and flutter will be come approximately the same as a result of which defe ctive portion will be doubly superposed and preferable portion vice versa The N 481 employs 2 capstans each having different diameter and rotations thereby avoiding 4 Erase Head Height and Tilt Adjus...

Page 7: ...Stop position gets released and the Head Base will slowly come out for playing To explain this function first the Head Base is latched and the Reel Motor begins to turn Then the Pressure Roller will be pushed and the Brake will be released Now the tape begins to run If you press the Pause Switch at this stage it comes to Pause mode Brake operates and the Pressure Roller moves away from the Capstan...

Page 8: ...ad gap loss and improve frequency response at high L101 and C186 compose a bias trap circuit and prevent bias leakage from playback eq amp circuit Playback eq amp gain adjustment should be performed so as to obtain 100 mV at TP101 TP201 by adjusting VR101 VR201 during the course of playing back 400 Hz Level Tape DAO9005A Eq Switch 70 us 1 20 us is connected to the playback eq amp circuit and the o...

Page 9: ...rd must also be changed Therefore even though record and playback is made by the method other than the IEC Standard no deterioration of frequency response or level difference will occur Any other method for instance record and playback on ferric oxide tape with putting Tape Switch on EX and Eq Switch on at 70 us When Nakamichi EX or EXII Tape is used at Tape Switch EX and Eq Switch 70us S N ratio ...

Page 10: ...resonance frequency at 21 kHz or neighborhood L105 C138 and C139 compose a recording bias trap cir cuit 2 2 3 Bias Oscillation Circuit Fig 2 2 5 shows a push pull oscillator with an oscillation frequency of 105 kHz which is constructed by capacitors C302 and C303 coupling the collectors and bases of two transistors Q301 and Q302 This is used to provide recording bias and as an erase sig nal By pre...

Page 11: ...hile FF mode 2 Auto Shut off Function Refer to Fig 2 3 1 basic circuit diagram During FF REW or PLAY PLAYBACK or RECORD mode auto shut off will be activated when the tape comes to end and FF REW or PLAY mode is changed to STOP mode Following explanation is made in regard to REW mode In the initial condition Q428 is turned ON and 24 VS is applied to the emitter of Q402 When Rewind Button is pressed...

Page 12: ...up reel and the intermittent flashes coming through the disc are converted into electrical signals by a phototransistor Q450 These signals are amplified into square waves and transmitted to the shut off detecting circuit in the subsequent stage When the tape end comes the take up reel and the disc stops rotating and no pulse is output from the sensor Meanwhile the Power mute L pulse is applied to ...

Page 13: ... resulting in C412 being charged continuously When the voltage of C412 exceeds the sum of the emitter voltage approx 5 5 V and the VBE of Q430 Q430 is turned ON and the base current flows to 0429 Con sequently Q429 is turned ON Q428 is cut off 24 VS is shut off PLAY mode is changed to STOP mode and play lamp goes out Q430 Q429 Q428 R476 R474 R456 and C420 consist of a Schmitt circuit which provide...

Page 14: ...since the base current to Q427 is supplied from C411 through R469 R427 is turned ON until the discharge of C411 is completed When the voltage of C411 is lower than the emitter voltage approx 4 2 V of Q430 Q430 and Q429 are cut off Q428 is turned ON and 24 VS is supplied as a result the PLAY signal becomes H 24 VS and PLAY mode is set 2 From RECORD mode to FF or REW mode When mode is changed from R...

Page 15: ... circuit is designed to protect from the erroneous setting of RECORD mode even if wrong record button operation is made Q422 is turned ON during FF or REW mode or when the cam is set to the play or pause position i e PLAY or PLAY PAUSE mode In this case as D422 is grounded by Q422 Q421 is not turned ON and the record lamp is not lit even if Record Button is further pressed Further the base of Q420...

Page 16: ... motor is driven until both inputs are balanced The cam control variable resistor VR601 moves synchronously with the motor so that the voltage at the sliding contact of VR601 is changed When the voltage at the sliding contact of VR601 is changed and the input difference of the differential amplifier IC402 1 2 becomes zero the control motor stops The following table shows the relationship between c...

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Page 18: ... position signal becomes H as a result Q417 is turned OFF and the reel motor is turned at a constantt speed by the governor composed of Q414 and Q415 During PLAY PAUSE mode Q412 is turned ON and the Pause position signal becomes L therefore Q417 is turned ON Q414 is biased in the reverse direction and Q414 is cut off thus the reel motor does not turn Take up function at loading When a cassette tap...

Page 19: ...y 90 degrees either clockwise or counter clockwise then disassemble F02 Power Switch Joint Bar from the Power Switch Knob Ass y 4 Remove F03 then disassemble F04 Front Panel Ass y 3 5 Headphone Jack Ass y Refer to Fig 3 2 1 Remove Front Panel Ass y referring to item 3 4 2 Remove F05 then disassemble F06 Headphone Jack Ass y 3 6 Mechanism Ass y Refer to Fig 3 2 1 Remove Front Panel Ass y referring ...

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Page 21: ...e P C B Ass y and Control Switch P C B Ass y Refer to Fig 3 3 1 Remove Control Switch Holder Ass y referring to item 3 10 2 Remove F10 then disassemble F11 Volume P C B Ass y 3 Remove F12 then disassemble F13 Control Button Spring 4 Remove F14 Control Button Shaft then disassemble F15 Control Buttons 5 Remove F16 then disassemble F17 Control Switch P C B Ass y 3 13 Rear Panel Ass y Power Transform...

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Page 23: ...ase Ass y 3 Remove F01 then disassemble the piston of the Pneumatic Damper Ass y 4 Remove F02 and F03 Cassette Case Holder L Ass y then disassemble F04 Cassette Case Ass y 5 Remove F05 then disassemble F06 Cover Plate Ass y 3 15 Tape Counter Ass y Refer to Fig 3 5 1 Refer to Fig 3 2 Remove Meter Ass y referring to item 3 7 2 Remove F07 then disassemble F08 Tape Counter Ass y ...

Page 24: ...ing to item 3 16 2 Remove F10 and F02 then disassemble F03 Sub Mechanism Chassis Ass y 3 18 Control Motor Ass y and Reel Motor Ass y Refer to Fig 37 1 Remove Sub Mechanism Chassis Ass y referring to item 3 17 2 Remove F04 then disassemble F05 Control Motor Ass y 3 Remove F06 then disassemble F07 Reel Motor Ass y 3 19 Cam Control Volume Refer to Fig 3 7 1 Remove Sub Mechanism Chassis Ass y referrin...

Page 25: ... Head Mount Base Ass y 3 23 Pressure Roller Ass y and Erase Head Refer to Fig 3 8 1 Remove Head Mount Base Ass y referring to item 3 22 2 Remove F03 and a washer then disassemble F04 Supply Pressure Roller Ass y 3 Remove F05 then disassemble F06 Erase Head 4 Remove F07 and a washer then disassemble F08 Take up Pressure Roller Ass y 3 24 Playback Head Ass y and Record Head Ass y Refer to Fig 3 8 1 ...

Page 26: ...uency Response Tape DA09003A 18 Reference EXII Tape DA09O21A 19 Reference SX Tape DA09025A 20 Reference ZX Tape DA09037A 21 Tilt check Gauge M 9039 DA09039A 22 EH Tilt Check Gauge M 9040 DA09O4OA 23 EH Stroke Check Gauge M 9042 DA09042A 24 EH Stroke Check Gauge M 9051 DA09O51A 25 Stroke Check Gauge M 9047 DA09047A 26 Record Head Mounting Gauge M 9048 DA09048A 27 Audio Analyzer T 1 00 including Dis...

Page 27: ...a range of F PS or R mark respectively f If out of the range precise adjustment for each position according to 2 Offset Fine Adjustment of Control Motor Driver will be required 2 Offset Fine Adjustment of Control Motor Driver Adjust only if a satisfactory result is not obtained in 1 Offset Adjustment of Control Motor Driver This adjustment is made by changing the value of the fixed resistors on th...

Page 28: ...tip press the Record and Play Switches to set the N 481 in record mode c Turn the Cam and bring the PY mark toward the pointer by hand Reel Motor will rotate before the PY mark reaches the pointer Adjust the value of R436 so that the voltage at the sliding contact of VR601 becomes 9 7 V 0 3 V when Reel Motor starts rotation d Observe the mute signal at the Q416 collector Turn the Cam referring to ...

Page 29: ... the original place to be in contact with record head and play back head surfaces after play mode is securely locked 5 Check to insure freedom from contact between the Gauge and pad lifter 6 Beacon Playback Head Lower will light on when height adjustment screw P turned clockwise but Playback Head Upper when counterclockwise Adjust so that both Upper and Lower will light on even when you move the s...

Page 30: ... guide thus check can be made on take up tape guide height d If the take up tape guide is misaligned the Take up Tape Guide Check Bar will not come into the take up tape guide If such is noted turn to adjust the height adjustment nut B till the Take up Tape Guide Check Bar is accepted by the take up tape guide e If the above are insured set the N 481 in pause mode then in play mode to see whether ...

Page 31: ...ockwise to light on Beacon 2 Excessive turning will cause the Beacon 1 to light off Adjustments of Screw Tilt will therefore be conducted till both of the Beacons 1 and 2 illuminate 6 Turn Screw Azimuth counterclockwise or clock wise to light on Beacon 3 Excessive turning will cause either Beacon 1 or 2 to light off and therefore adjust with Screw Azimuth until all of the 3 Beacons 1 2 and 3 illum...

Page 32: ... set the N 481 in record and play mode c Feed in 400 Hz 0 dB then turn the RH Height Gear until the output of both channels becomes maximum d Feed in 15 kHz 20 dB then turn the RH Azimuth Alignment Screw until the output of both channels becomes maximum e Repeat c and d 1 2 times f After completion of both adjustment and alignment feed in 400 Hz 0 dB and record it to the same portion of both A and...

Page 33: ...ate 7 Remove the R 8L record head assembly from the Mounting Gauge Plate 8 Readjustment of Record Head Mounting Gauge M 9048 DA09048A a Mount the Block B onto the Mounting Gauge Plate b Loosen the 2 screws fixing the Block A c As shown in the Fig 5 14 hold the Gauges 3 05 mm and either one of 0 05 0 15 0 2 0 25 0 3 or 0 35 mm thickness between the Block A and Block B fix the Block A with screw pus...

Page 34: ...eight Adjustment and Azimuth Alignment 5 8 Record Head Stroke Adjustment etc will be required As a case may be the said waving or slippage may have been caused from defective supply Pressure Roller Ass y or Take up Pressure Roller Ass y without parallel contact with capstans If such are noted the Pressure Roller Assemblies will have to be replaced Further excessively weak take up torque or strong ...

Page 35: ...urning the Eject Arm in the illustrated direction then set the N 481 in playback mode 2 With pushing the Eject Arm by hand loosen the screw and then pull the Eject Wire in the direction of the arrow until it stops as shown in Fig 5 19 2 3 Tighten the screw then apply a quantity of lock tight paint 5 13 Lubrication N 481 is a lubrication free cassette deck except when parts are replaced Apply the f...

Page 36: ...6 PARTS LOCATION FOR ELECTRICAL ADJUSTMENT ...

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