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CONTENTS
1. General ................................................................................................. 3 2. Principle of Operation ............................................................................ 4 2. 1. Mechanisms ............................................................................ 4 2.1.1. Headblock ................................................................. 4 2.1.2. Erase Head ................................................................. 5 2.1.3. Double Capstan Tape Drive ....................................... 5 2.1.4. Mechanism Control Cam Operation .............................. 6 2. 2. Amp. Circuits ............................................................................ 7 2.2.1. Playback Eq. Amp. Circuit ............................................ 7 2.2.2. Record Eq. Amp. Circuit ................................................... 9 2.2.3. Bias Osc. Circuit ................................................... 9 2. 3. Mechanism Control Circuits ................................................... 10 2.3.1. Outline ............................................................... 10 2.3.2. +12 v Power Source ...................................................... 11 2.3.3. Power-mute Signal ...................................................... 11 2.3.4. Auto Shut.off Circuit ...................................................... 11 2.3.5. Record Control Circuit ...................................................... 14 2.3.6. Mute Signal ............................................................... 14 2.3.7. Control Motor Drive Circuit .......................................... 15 2.3.8. Reel Motor Governor ...................................................... 16 3. Removal Procedures ........................................................................... 17 3. 1. Cassette Case Cover Ass'y ............................................................... 17 3. 2. Top Cover Ass'y .................................................................. 17 3. 3. Bottom Cover Ass'y .................................................................. 17 3. 4. Front Panel Ass'y .................................................................. 17 3. 5. Headphone Jack Ass'y .................................................................. 17 3. 6. Mechanism Ass'y ............................................................................. 17 3. 7. Meter Ass'y ............................................................................. 17 3. 8. Lamp P.C.B. R Ass'y and Lamp P.C.B. L Ass'y ................................. 17 3. 9. Main P.C.B.Ass'y ............................................................................. 17 3. 10. Control Switch Holder Ass'y ....................................................... 17 3. 11. 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 Idler Ass'y ...................................................... 20 3. 21. Cam Drive Gear and Control Cam ............................................. 20 3. 22. Head Mount Base Ass'y ................................................................... 20 3. 23. Pressure Roller Ass'y and Erase Head .............................................. 20 3. 24. Playback Head Ass'y and Record Head Ass'y ................................... 20 4. Measurement Instruments ................................................................... 21 5. Mechanical Adjustments ................................................................... 21 5. 1. Mechanism Control Cam Adjustment ............................................. 21 5. 2. Tape Speed Adjustment ................................................................... 22 5. 3. Record Head and Playback Head Tilt Adjustment ................................... 23 5. 4. Head Base Stroke Adjustment ......................................................... 24 5. 5. Tape Guides Adjustment and Erase Head Stroke Adjustment ............. 25 5. 6. Erase Head Height and Tilt Adjustment ............................................. 26 5. 7. Playback Head and Record Head Height Adjustment and Azimuth Alignment 27 5. 8. Record Head Stroke Adjustment ....................................................... 28 5. 9. Tape Travelling Adjustment.................................................................. 29
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5. 10. Record Switch Linkage Adjustment .................................................................. 29 5. 11. Flywheel Holder Adjustment ........................................................................ 30 5. 12. Eject Wire Adjustment .................................................................................... 30 5. 13. Lubrication ................................................................................................ 30 6. Parts Location for Electrical Adjustment .................................................................. 31 7. Electrical Adjustments and Measurements ........................................................................ 32 7. 1. Adjustment and Measurement Instructions ................................................ 32 7. 2. Playback Frequency Response Adjustment ................................................ 35 7. 3. Check on Dolby NR Circuit ............................................................................... 35 8. Mounting Diagrams and Parts List ............................................................................... 36 8. 1. Volume P.C.B. Ass'y ...............................................................................36 8. 2. Control Switch P.C.B. Ass'y ............................................................................... 36 8. 3. Switch P.C.B. Ass'y ..................................................................................... 36 8. 4. Control P.C.B. Ass'y ..................................................................................... 36 8. 5. Auto Shut-off P.C.B. Ass'y ............................................................................... 36 8. 6. Lamp P.C.B. L Ass'y ..................................................................................... 36 8. 7. Lamp P.C.B. R Ass'y ..................................................................................... 36 8. 8. Main P.C.B. Ass'y ........................................................................................... 37 9. Mechanism Ass'y and Parts List ..................................................................................... 41 9. 1. Synthesis ................................................................................................. 41 9. 2. Front Panel Ass'y (A01) ............................................................................... 41 9. 3. Synthesis Mechanism Ass'y (A02) ................................................................... 41 9. 4. Meter Escutcheon Ass'y (B01) ......................................................................... 42 9. 5. Control 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 9. 17. Take-up Pressure Roller Ass'y (F03) ................................................................... 50 9. 18. Head Base Ass'y C (F04) ............................................................................... 51 9. 19. Cassette Case Holder L Ass'y (F05) ................................................................... 51 9. 20. Cassette Case Holder R Ass'y (F06) ................................................................... 51 9. 21. Auto Shut-off Ass'y (F07) ............................................................................... 51 9. 22. Pneumatic Damper Ass'y (F08) ......................................................................... 51 9. 23. P-8L Playback Head Ass'y (G01) ................................................................... 51 9. 24. R-8L Record Head Ass'y (G02) ......................................................................... 51 10. Overall Timing Chart ................................................................................................. 53 11. Eq.Amp. Frequency Response ..................................................................................... 54 11. 1. Playback Frequency Response ......................................................................... 54 11. 2. Record Current Frequency Response ............................................................. 54 12. Wiring Diagram ......................................................................................................... 55 13. Block Diagrams ......................................................................................................... 57 13. 1. Amplifier ................................................................................................. 57 13. 2. Mechanism Control ..................................................................................... 58 14. Schematic Diagrams ................................................................................................. 59 15. Specifications .........................................................................................................62

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2. PRINCIPLE OF OPERATION
2.1. Mechanisms 2.1.1. Headblock Refer to Fig. 2.1.1 Headblock. Nakamichi 481 Headblock provides more stabilized tape travel. Accuracy of tape travel is one of the most essential factors for a device to optimize its performance. Inaccurate tape travel will therefore induce deterioration exemplified by the following: (a) vibration will be given to tape travel, as a result of which flutter and modulation noise will become in creased (b) insufficient tape-to-head contact will result in level drops (c) tape skew will become greater and frequency response will become decreased Needless to say, constant tape travel must consist of smooth drive mechanism, as well as of the fact that tape, heads and tape guide are placed in the most appropriate positions. N481 Playback Head and Record Head, they are both made small in size so that the both heads are assembled in a space of the conventional Record/Playback Head. Erase Head is located at the place where the Record Head is located in the N-700II/1000II. Both Playback Head and Record Head are assembled on the Head Mount Base. Take-up Tape Guide and Supply Tape Guide are fixed to the Take-up Pressure Roller Arm and Supply Pressure Roller Arm, respectively. Erase Head is placed on the Head Base. All these can be separately adjusted. Record Head is placed slightly backward, approximately 0.15 mm away from the Playback Head. Record Head is placed approximately 3° inclined leftward. Shape of the Heads and its location have been carefully studied to bring about smoother contact of tape with the Heads. Pad Lifter is affixed to the Playback Head so as not to let Tape Pad touch the Head to give more stabilized tape travel, making it free from the influence of the Tape Pad within the Cassette Tape. Thus the trouble of changes in azimuth 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 is assembled into the Take-up and Supply Pressure Roller Assemblies. With a spring in the stud of Mechanism Chassis Ass'y, Pressure Roller Ass'y is tightly affixed with Tape Guide Adjustment Nut. The Adjustment Nut is placed on a spring through Pres sure Roller Arm, and therefore by either tightening or loosening, height adjustment of the Tape Guide will become possible. (2) Playback Head Height Adjustment and Azimuth Alignment Azimuth and height of Playback Head can be made in dependently and adjustment may be done separately without affecting others. In order to adjust the tilt of Playback Head backwards or frontwards, take off the Height Gear Stopper and take out the Height Gear and then turn the two Height Adjustment Screws. After the adjustment is done, place the Height Gear back and fix it with the Height Gear Stopper. After the tilt is adjusted in such a way as above, adjust the height by loosening or tightening the Height Gear. Azimuth alignment is adjusted by loosening or tightening the PH Azimuth Screw. This system has been carefully designed so as to minimize in -fluence each other between azimuth and height adjust -ment. (3) Record Head Height Adjustment and Azimuth Alignment Record head tilt adjustment can be performed in the same way as for the Playback Head. Height adjustment can be adjusted while recording 400 Hz test tone by loosening or tightening RH Height Adjust ment Screw to obtain the maximum level on the both Level Meters. Azimuth alignment can be adjusted while playing back 15 kHz signal by loosening or tightening RH Azimuth Alignment Screw to obtain the maximum

level on the both Level Meters. This system has also been carefully designed so as to minimize influence each other between azimuth and height adjustment. 2.1.2. Erase Head Fig. 2.1.3 shows the sectional view of the Erase Head. Fig. 2.1.4 shows the characteristics of erasing current and erasure.

assembled with the Head Base. It is installed with three screws. By turning these screws, its height, tilt of back ward or frontward, and tilt of leftward or rightward can be adjusted separately, thus the best location of Erase Head can be obtained. the aforesaid occurrence and stabilizing wow and flutter characteristics.

It has the same characteristics with the previous type Direct-Flux Erase Head but been purposely developed to minimize the size further. Conventional Erase Head had its inside core narrower than its outside core, while this Erase Head is equipped with an inside core wider than the outside core. This has resulted more power sufficient enough for erasing with small power consumption, approx. 0.5 W, though the head width is as small as 3 mm. The smaller the power con sumption is, the smaller will be the heat generation, and this is of course another merit.

2.1.3. Double Capstan Tape Drive As shown in Fig. 2.1.5, the double capstan system con sists of two capstan shafts (a) and (b) connected to the two flywheels which are driven by a capstan belt. Against these capstans two pressure rollers (a) and (b) are engaged to run the tape with an adequate holdback ten sion created by the double capstan and pressure rollers. Since the diameter of capstan shaft (a) is smaller than that of capstan shaft (b), when two flywheels begin to turn as shown in the figure, capstan (a) runs slightly faster than capstan (b), which subsequently 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 Adjustment Erase Head is affixed onto the Erase Head Plate which is

As the double capstan system always creates a constant and stable holdback tension between the two capstans, the condition of the tape between two capstans will not be affected by any external conditions such as irregular take-up and supply torques, irregular loading of cassette tape, undesirable mechanism vibration and etc., thus assuring the superior wow and flutter characteristics. The double capstan system provides a constant holdback tension on the tape and maintains the stable pressure onto the tape against the heads. The only critical factor in the double capstan system is to be considered; the two capstans have to be positioned per fectly in parallel and to be precisely vertical against the head base, the pressure rollers have to be evenly pressed against the capstan shafts and the head surface must be

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positioned perfectly vertical to the tape surface. Otherwise, the running tape might become out of the tape guide resulting in irregular movement.

2.1.4. Mechanism Control Cam Operation Refer to Fig. 2.1.6 Mechanism Control Cam timing chart. Function of N-481 Mechanism is done by Cam Control. Cam is driven by the Control Motor. The Motor operates so as to result zero in the difference of voltages between each voltage corresponding to mechanism function and each reference voltage which corresponds to each commands of the Control Switch. When the difference comes to zero, then it stops. In this way, each function is kept properly operated. For further details, please see the explanation on Logic Control. Here we explain principle of its mechanical functions. Cam Control System works as follows: Cam Drive Gear is driven by Control Motor by means of Drive Belt. Cam Drive Gear is related to the cam with which each function may be mechanically set on. (1) Play Mode Press the Play Switch to make it Play mode. Then the Cam begins to move from Stop position to Play position and the Play mode will be set. The Head Base which is linked to the Cam and which is normally pushed against the 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 and the Reel Motor stops. Play mode may be changed to Stop mode by pressing the Stop Switch, and latch of the Head Base being released. The Cassette Case cannot be opened because of the latched eject effect unless it is in Stop mode. (2) Record Mode By pressing the Record Switch and the Pause or Play Switch, it may be made to Record mode. The Cam at this moment moves from Stop position to Rec. position. At the same time, Rec. Trigger Mechanism is driven and the Record Switch on the Main P.C.B. is switched on to the Record side. Further, the Cam turns until it comes to the Pause or Play position. On the other hand, the Rec. Trigger Mechanism is released during this process. When the Cam is set in Rec./Pause or Rec./Play position, Record signals will be sent to Bias Oscillating Circuit from Logic Control Circuit to let the Bias to oscillate. Press the Stop Switch and the Cam comes back to the Stop position. At the same time, it will set the Record Switch on the Main P.C.B. to the Play side.

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(3) F.F. or Rewind Mode By pressing the F.F. or Rewind Switch, it comes either to F.F. or Rewind mode. The only difference of these two modes is that one is to turn the Reel Motor reverse and the other to transmit the torque against the Reel Hub onto the take-up side or to the supply side. Brake is re leased at this stage and the Reel Motor begins to turn F.F. or Rewind.

(4) Pause Mode Press the Pause Switch to make it to Pause mode. In changing it from Stop mode to Pause mode, the Brake is first released, then the Head Base is latched, and again the Brake works. At this stage, the Reel Motor would not turn with the Pressure Roller being apart from the Capstan, and the tape would remain still.

2.2. Amp. Circuits 2.2.1. Playback Eq. Amp. Circuit Fig. 2.2.1 shows the playback equalizer amp. circuit. Fig. 2.2.2 shows its system diagram, and Fig. 2.2.3 shows the time constant of equalizer. Playback Head is connected to the input of this circuit. Amplifier, which is composed of Q101 and Q102, is an equalizer amplifier and its time constant is shown in Fig. 2.2.3. R111, R112, L101 and C109, which consist of a peaking circuit, compensate playback head 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 overall time constant of playback eq. amp. circuit will become as follows:

Tape SW ZX SX

Eq. SW 70us 70us

Tape Nakamichi ZX Nakamichi SX, TDK SA, Maxell XL-II Scotch Master 70 us Low-Noise High-Density (including EX, EXll, TDK AD, Maxell XL-l, Scotch Master 120 us) Nakamichi EX, EXII

EX

120us

70 us

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It is specified in the IEC Standard that the time constant is 120 us on tapes of ferric oxide, and 70 us on tapes of Cr02. However, in the case of Eq. Switch on N-481, when time constant at playback is changed, at the same time constant at record 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 will be improved by approximately 4 dB (WTD).

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2.2.2. Record Equalizer Amplifier Circuit The record equalizer amplifier circuit consists of the Out put Amp. incorporated in the Dolby NR IC and peripheral circuits as shown in Fig. 2.2.4. VR102, VR103, and VR104 are the record calibration semi-fixed volumes for ZX, SX and EX tapes. The output of the Output Amp. is given to these volumes, and the outputs from the volumes are fed back to the inverting input of the Output Amp. via amplifier Q103 and a time-constant changeover circuit. By adjusting L104, compensation for the high frequency range is made by setting a resonance frequency at 21 kHz or neighborhood. L105, C138 and C139 compose a recording bias trap circuit.

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 pressing the Record and Pause, or Record and Play Buttons, (Play+ Pause)-position signal conducted from the Logic P.C.B. Ass'y becomes H and Q303 turns to ON. Therefore, +24 V is applied to the circuit, as a result of which oscillation begins. When the record mode is released, oscillator output is damped by the discharge of C304. This prevents mag -netization of the Record Head.

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2.3. Mechanism Control Circuits 2.3.1. Outline (1) Control Button Operation Record, Rewind, Stop, Play, and Fast-Forward Buttons consist of a 5--way switch and are interlocked each other. When one button is pressed, it is mechanically locked in the ON state and other buttons are mechanically released. Stop Button is of momentary type and acts to release other buttons mechanically. But it is not used to control circuits electrically. Pause Button is independent from others and is of push-on and push-off type. Note that if two or more buttons are pressed simultaneously, these buttons are locked in the ON state. Under the normal con trol button operation, only Record and Play Buttons are pressed simultaneously to set the N-481 in RECORD mode. In this case, both Record and Play Buttons are locked in the ON state and RECORD mode is set. The N-481 is designed so as not to occur erroneous operation even if two or more buttons are pressed simultaneously. Further, to prevent from abnormal tape tension, loosening of tape, etc., the N-481 changes its mode by passing through momentary STOP mode automatically, for ex ample, when PLAYBACK mode is commanded while FF mode, or REW mode is commanded while 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, it is locked in the ON state, as a result, Q402 is turned ON, the REW signal becomes H, and the N-481 is set in REW mode. When tape-end comes, auto shut-off is activated and Q428 is turned OFF, as a result, +24 VS is shut-off, Q402 is cut off, and the REW signal becomes L. In this way, REW mode is changed to STOP mode. (Note that Rewind Button is still locked in the ON state.) When Play Button is pressed in this state, REW Button is released and Q428 is turned ON, as a result, +24 VS is applied again, Q418 is turned ON, the PLAY signal becomes H, and the N-481 is set in PLAY mode. (3) Unattended Recording or Playback Unattended recording or playback is carried out by the use of the lock mechanism of control button, therefore, no special circuit is required for this purpose. If Record and Play Buttons are pressed, unattended re cording can be carried out when the power is connected to the N-481. If only Play Button is pressed, playback will be carried out when the power is connected to the N-481.

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2.3.2. +12 V Power Source Refer to Fig. 2.3.2 circuit diagram. Only +24 V DC power supply is used in the N-481. The circuit acts to produce a +12 V power source from the +24 V DC power supply. Mechanism control is done by using thus produced +12 V. 2.3.3. Power-mute Signal Refer to Fig. 2.3.3 circuit diagram and Fig. 2.3.4 timing chart. Power-mute = L signal is produced pulse-likely when Power Switch is turned ON or OFF. This L pulse mutes the amp, circuit and also acts to shut off the shut off circuit initially. (1) Power Switch ON Q433 is turned ON at every positive half cycle of the out put from the secondary winding of the power transformer. When Q433 is turned ON, C416 is discharged, as a result, the voltage of C416 can not exceed the VBE of Q432, and Q432 is in the cutoff state. Therefore, the Power-mute =L pulse is produced for a certain period of time when +24 V is built up after Power Switch is turned ON. The Power-mute= Lsignal makes Q4l6 to turn ON, as a re -sult, Mute signal becomes H and the amp. circuit is muted.

Meanwhile, the Power-mute = L pulse is applied to the shut-off circuit and shut-off is activated. (2) Power Switch OFF The output from the secondary winding of the power transformer ceases quickly, and Q433 is turned OFF. Consequently, the base current flows to Q432 through R481, Q432 is turned ON, and the Power-mute signal becomes L. The Power-mute = L signal makes Q416 to turn ON, as a result, Mute signal becomes H and the amp. circuit is muted. At the same time, shut-off circuit is shut off by the Power-mute = L signal.

2.3.4, Auto Shut-off Circuit Refer to Fig. 2.3.5 circuit diagram and Fig. 2.3.6 timing chart. (1) Shut-off Sensor Light from lamp PL407 is projected through holes in a disc rotating synchronously with the take-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.

(2) Shut-off Detecting Circuit and Peripheral Circuits Shut-off conditions are as follows: o reached tape-end during PLAY (PLAYBACK or RECORD), FF, or REW mode o mode is changed as follows: from FF to REW mode, or vice versa from FF to PLAY mode from RECORD mode to FF or REW mode When the mode is changed, shut-off is momentarily activated and the mode is changed to STOP mode in a short period of time, and after this STOP mode is over, a new mode is set. 0 Power-mute = L pulse is generated when Power Switch is turned ON or OFF 0 memory rewind function is activated.

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(a) Reached tape-end during PLAY (PLAYBACK or RECORD), FF, or REW mode Explanation is made for PLAY mode as an example. For FF or REW mode, the shut-off function is the same as for PLAY mode. As Play Button is locked ON mechanically, Kplay = L. Accordingly, R488 (100 kohm) is grounded through Play Button and the voltage at the point A becomes approx. +23 V. Since the voltage at the point A is not lower than the emitter voltage of Q424, Q424 is turned OFF and Q426 is also turned OFF. (Q424 and Q426 will be turned ON when the voltage at the point A is further lowered as described in subsequent (b).) Q425, Q427, Q430, R470 and C412 consist of a shut-off detecting circuit. During PLAY mode, the voltage at the point A is approx. +23 V. therefore, Q425 is turned ON and C412 (2.2 pF) is charged toward +24 V through R470. Meanwhile, pulses from the shut-off sensor are applied to the base of Q427 through R489 and C418, and, at every H cycle of the sensor output pulse, Q427 is turned ON and C412 is discharged through Q427. When the tape-end is detected, pulses from the shut-off sensor are not transmitted and Q427 is turned OFF, 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 provides hysteresis characteristics for ON/OFF of Q430. Accordingly, Q430 will be turned ON or OFF without chattering for the input waveform with a large time constant developed across C412. If Pause Button is pressed during PLAY mode, tape stops and no pulse is transmitted from the shut-off sensor, but Q427 is kept ON since Q423 is turned ON during PLAY.PAUSE mode, therefore, no charge is made at C412 and shut-off is not activated. When shut-off is made at the tape-end during PLAY mode, PLAY mode is changed to STOP mode. If Stop Button is further pressed, Play Button will be re leased and the voltage at the point A returns to +24 V as R488 is released from grounding, as a result, Q425 is turned OFF and C412 is discharged quickly through D423 and R467 (10 kohm). Accordingly, Q430 is turned OFF, Q429 is turned OFF, Q428 is turned ON, and +24 VS is again applied preparing for the next control button operation.

(b) Mode is changed 1) From FF to REW mode, or vice versa, or from FF to PLAY mode Refer to Fig. 2.3.7 timing chart. When mode is changed from FF to REW mode, or vice versa, or from FF to PLAY mode, momentary STOP mode is automatically taken in view of the response of the tape deck mechanism, and after this is over, a new mode is set. The following explains in regard to the case when FF mode is changed to PLAY mode by pressing Play Button during FF mode: During FF mode, R486 (100 kohm) is grounded by the NOT Kf.f. = L signal. When Play Button is pressed, it is locked ON and FF Button is released. Although FF Button is re leased, the NOT Kf.f. signal is kept L for a short period of time because the delay circuit (C605 and R608) connected in parallel to FF Button acts to prolong the NOT Kf.f = L signal. In this period, the voltage at the point A becomes approx. +22 V from +23 V pulse-likely as R486 and R488 are grounded by the NOT Kf.f = L and NOT Kplay = L signals respectively. Consequently, Q424 and Q426 are turned ON, and C411 is charged up to +24 V, but C411 will be discharged after this period is over. The base current to Q430 is supplied from C411 through D424 and R475, as a result, Q430 and 0429 are turned ON, Q428 is turned OFF, and +24 VS is shut off resulting in STOP mode. On the other hand, 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 RECORD to FF or REW mode, momentary STOP mode is automatically taken in view of the tape deck mechanism, and after this is over, a new mode is set. When Record Button is released by pressing either FF or REW Button, Q419 is turned from ON to OFF, therefore, a negative differentiated pulse is applied to the point A via C421 (22 uF). This negative pulse acts to turn ON Q424 and Q426, as a result, C411 is charged up to +24 V. FF or REW mode is set after passing through a certain period of STOP mode in the same manner as above (1). (c) Power-mute = L The Power-mute = L pulse is generated when Power

Switch is turned ON or OFF. During the Power-mute sig -nal is L, the voltage at the point A becomes lower than the emitter voltage of Q424. Subsequently, Q424 and Q426 are turned ON, C41 1 is charged up to +24 V, and shut-off is activated in the same manner as above (b). (d) Memory Rewind During REW mode and with Memory Rewind Switch turned ON, C414 is grounded when the tape counter

comes to "999" and Q431 is turned ON pulse-likely. As a result, Q430 is turned ON, and shut-off is activated resulting in STOP mode.

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2.3.5. Record Control Circuit Refer to Fig. 2.3.8 circuit diagram. RECORD mode is set by pressing Record Button, then Play Button together. By pressing Record Button, the Krec. signal becomes L, Q419 is turned ON, Q421 is turn ed ON, and the record lamp is illuminating. Then, by pres sing Play Button further, the Kplay signal becomes L,Q418 is turned ON, the PLAY signal becomes H (+24 VS), and Q420 is turned ON. Accordingly, the base current flows to Q403 via C406 connected to the base of Q403, and Q403 is turned ON pulse-likely. The output of Q403 is fed to the control motor drive circuit and acts to bring the cam to the record position, When Q403 returns to OFF, the cam then moves to the

play position and stays there, thus the mechanism is set to RECORD mode. Record 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 is grounded via D419 and Q422, consequently, Q420 and Q403 are not turned ON and no pulse is output from Q403 to the control motor drive circuit.

2.3.6. Mute Signal Refer to Fig. 2.3.9 circuit diagram. When Q416 is turned ON, the Mute = H signal is fed to the amp. circuit and the amp. circuit is muted. The condition that the amplifier circuit is muted are (Mute = H):

R/P Switch : When R/P Switch on the Main P.C.B. is in the record position, +24 V is applied, but when it is in the play position, no voltage is applied. The modes in which the amplifier circuit is not muted are

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2.3.7. Control Motor Drive Circuit Refer to Fig. 2.3.10 circuit diagram and Fig. 2.3.11 timing chart. The control motor is turned by varying amounts, according to which control button is set. This motor is connected to the mechanism control cam, and the mechanism is set to the mode indicated by this cam. The motor is driven by the differential amplifier IC402 (1/2) and drivers Q405 and Q406. In the control motor stop condition, both voltages at pins No.5 (non-inverting input) and No.6 (inverting input) of lC402 (1/2) are equal and the difference of both inputs is zero. When a new mode is demanded, the balance of both inputs is broken, as a result, the control 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 Mode Record Stop FF/REW Play/Pause Play ON Q403, Q410 pulse Q404, Q410 D417 ON

amplifier IC402 (1/2) becomes zero, the control motor stops. The following table shows the relationship between cam position and the voltage at the sliding contact of the cam control variable resistor VR601, and the state of transistors in each mode. Position on Cam Record Stop FF/REWPause Play Typical Voltage at Sliding Contact of Corn Control Volume 16V 15V 13.5V I0V 7.5V

Q412 Q412 Q412 Q411, Q412 Q411

OFF Q404 Q403, Q404,Q410 Q403 Q403, Q404, Q410 Q403, Q404, Q410

Q411 Q411 Q411 Q412

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2.3.8. Reel Motor Governor Refer to Fig. 2.3.12 circuit diagram. One end of the reel motor is connected with +12 V and the other end is a terminal for controlling. During FF mode, Q413 is turned ON and the reel motor is grounded. Accordingly, the reel motor turns in the direction of fast-forwarding. On the other hand, during REW mode, +24 V (REW H) is applied to the reel motor and the reel motor turns in the direction of rewinding. During PLAY (PLAYBACK or RECORD) mode, Q412 is turned OFF and the Pause-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 tape is inserted and loaded, Eject Switch will become open. Consequently, the base current is applied to Q413 through C409, and Q413 is turned ON pulse-likely. During Q413 is turned ON, the reel motor turns in the direction of fast-forwarding and eliminates tape loosening of the cassette tape if any.

3. REMOVAL PROCEDURES
3.1. Cassette Case Cover Ass'y Refer to Fig. 3.1. (1) Press the Eject Button to open the Cassette Case Ass'y. (2) Pull out F01 (Cassette Case Cover Ass'y) upwardly. 3.2. Top Cover Ass'y Refer to Fig. 3.1. Remove F02 and F03, then disassemble F04 (Top Cover Ass'y). 3.3. Bottom Cover Ass'y Refer to Fig. 3.1. Remove F05, then disassemble F06 (Bottom Cover Ass'y). 3.4. Front Panel Ass'y Refer to Fig. 3.2. (1) Refer to Fig. 3.1. Remove Top Cover Ass'y and Bottom Cover Ass'y referring to items 3.2 and 3.3. (2) Pull out F01 (Volume Knobs). (3) Remove F02 (Power Switch Joint Bar) by releasing the self-interlocking pin of the Power Switch Joint Bar from Power Switch, and turn F02 (Power Switch Joint Bar) by 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 to item 3.4. (2) Remove F07 and F08, then disassemble F09 (Mechanism Ass'y including 5 connectors and record switch linkage). 3.7. Meter Ass'y Refer to Fig. 3.2. (1) Remove Front Panel Ass'y referring to item 3.4. (2) Remove F10 (Meter Ass'y) by releasing self-interlocking pins of the Meter Ass'y. 3.8. Lamp P.C.B. R Ass'y and Lamp P.C.B. L Ass'y Refer to Fig. 32. (1) Remove Meter Ass'y referring to item 3.7. (2) Remove F11 (Lamp P.C.B. R Ass'y) and F12 (Lamp P.C.B. L Ass'y) by releasing the self-interlocking pins.

3.9. Main P.C.B. Ass'y Refer to Fig. 3.3. (1) Refer to Fig. 3.2. Remove Front Panel Ass'y referring to item 3.4. (2) Remove 5 connectors and the wires connected by wrapping from the F05 (Main P.C.B. Ass'y). (3) Remove F01, F02, F03, F04 and the Record Switch Linkage from the Wire Holder assembled with Record Switch, then disassemble F05 (Main P.C.B. Ass'y). 3.10. Control Switch Holder Ass'y Refer to Fig. 3.3. (1) Refer to Fig. 3.2. Remove Meter Ass'y referring to item 3.7. (2) Remove F06, then disassemble F07 (Control Switch Holder Ass'y). 3.11. Switch P.C.B. Ass'y Refer to Fig. 3.3. (1) Refer to Fig. 3.2. Remove Front Panel Ass'y referring to item 3.4. (2) Remove F08, then disassemble F09 (Switch P.C.B. Ass'y). 3.12. Volume 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 Transformer and Power Switch Refer to Fig. 3.4. (1) Refer to Fig. 3.1. Remove Top Cover Ass'y and Bottom Cover Ass'y referring to items 3.2 and 3.3. (2) Remove F01, F02 and F03, then disassemble F04 (Rear Panel Ass'y). (3) Remove F05 and F06, then disassemble F07 (Power Transformer). (4) Remove Power Switch Joint Bar by releasing the self-interlocking pin of the Power Switch Joint Bar from Power Switch and F08, then disassemble F09 (Power Switch Holder Ass'y). (5) Remove F10, then disassemble F11 (Power Switch).

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3.14. Cassette Case Ass'y and Cover Plate Ass'y Refer to Fig. 3.5. (1) Refer to Fig. 3.2. Remove Mechanism Ass'y referring to item 3.6. (2) Press the Eject Button to open the Cassette Case 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).

3.16. Capstan Motor Ass'y and Flywheel Ass'y Refer to Fig. 3.6. (1) Refer to Fig. 3.2. Remove Mechanism Ass'y referring to item 3.6. (2) Remove F01 and F02, then disassemble F03 (Fly wheel Holder Ass'y) and F08 (Capstan Belt). (3) Remove F04, then disassemble F05 (Capstan Motor Ass'y). (4) Remove F06, then disassemble F07 (Control P.C.B. Ass'y). (5) Remove F09 (Supply Flywheel Ass'y), then disassemble F10 (Take-up Flywheel Ass'y). (6) After removing both Flywheel Assemblies, disassemble F11 (Thrust Washer 3 mm), F12 (Thrust Washer 2.6 mm), F13 (Flange Thrust Caps) and F14 (Thrust Springs). 3.17. Sub Mechanism Chassis Ass'y Refer to Fig. 3.7. (1) Refer to Fig. 3.6. Remove Flywheel Assemblies refer ring 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 referring to item 3.17. (2) Remove F08, then disassemble F09 (Volume Coupler). (3) Remove F10, then disassemble Fl 1 (Cam Control Volume). 3.20. Reel Hub Ass'y and Idler Ass'y Refer to Fig. 3.7. (1) Remove Sub Mechanism Chassis Ass'y referring to item 3.17. (2) Remove F12 (Reel Hub Heads), then disassemble F13 (Reel Hub B Assemblies), F14 (Reel Hub Take-up Ass'y), F15 (Reel Hub Supply Ass'y), F16 (Back Tension Ass'y) and F17 (Back Tension Spring). (3) Remove F18, then disassemble F19 (Idler Ass'y).

3.21. Cam Drive Gear and Control Cam Refer to Fig. 3.7. (1) Remove Sub Mechanism Chassis Ass'y referring to item 3.17. (2) Remove F20, then disassemble F21 (Cam Drive Gear). (3) Remove F22, then disassemble F23 (Counter-Load Arm Ass'y). (4) Remove F24, then disassemble F25 (Control Cam). 3.22. Head Mount Base Ass'y Refer to Fig. 3.8. (1) Refer to Fig. 3.5. Remove Cassette Case Ass'y refer-ring to item 3.14. (2) Remove F01, then disassemble F02 (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) Remove Head Mount Base Ass'y referring to item 3.22. (2) Turn F09 by 90 degrees by pushing it, then disassemble F10 (Playback Head Ass'y). (3) Turn Fl 1 by 90 degrees by pushing it, then disassemble F12 (Record Head Ass'y).

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4. MEASUREMENT INSTRUMENTS

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27)

Audio Generator (20 Hz -- 200 kHz) AC Millivolt Meter (with dB measures) Oscilloscope (DC -- 5 MHz) Distortion Meter Speed & WOW/Flutter Meter Frequency Counter (DC -- 1 MHz) Ohm Meter DC Volt Meter AC Volt Meter Torque Gauge (DA09013A) 15kHz Azimuth Tape (DA09004A) 3 kHz Speed & Wow/Flutter Tape (DA09006A) 1 kHz Track Alignment Tape (DA09007A) 400 Hz Level Tape (DA09005A) 20 kHz PB Frequency Response Tape (DA09001A) 15 kHz PB Frequency Response Tape (DA09002A) 10 kHz PB Frequency Response Tape (DA09003A) Reference EXII Tape (DA09O21A) Reference SX Tape (DA09025A) Reference ZX Tape (DA09037A) Tilt check Gauge M-9039 (DA09039A) EH Tilt Check Gauge M-9040 (DA09O4OA) EH Stroke Check Gauge M-9042 (DA09042A) EH Stroke Check Gauge M-9051 (DA09O51A) Stroke Check Gauge M-9047 (DA09047A) Record Head Mounting Gauge M-9048 (DA09048A) Audio Analyzer T-1 00 (including Distortion, Wow/Flutter, Speed, Oscillator and dB meter)

Notes: 1. (10) -- (27) are the products of Nakamichi Corporation. 2. EH Stroke Check Gauge M-9042 (DA09042A) should be used for the Models from serial Nos. A30601001 to A30604798, and EH Stroke Check Gauge M-9051 (DA09O51A) is for the Models bearing serial Nos. A30604799 and greater.

5. MECHANICAL ADJUSTMENTS

5.1. Mechanism Control Cam Adjustment Before Adjustment, disassemble the Front Panel Ass'y then remove the Cover Plate Ass'y, referring to items 3.4 and 3.14. (1) Offset Adjustment of Control Motor Driver (a) Refer to Figs. 5.1 and 5.2. Adjust VR602 and VR603 on the Control P.C.B. to locate approximately at the middle of the variable range. Then turn ON the Power Switch. VR602 (for Cam position stop) VR603 (for Cam position play) (b) Press the Stop Switch to set the N-481 in stop mode. Adjust VR602 (for stop) so that the "S" mark on the Cam corresponds to the pointer on the mechanism chassis. (c) Press the Play Switch to set the N-481 in playback mode. (Cam will rotate, and the position marked with "PY" comes to the pointer.) Adjust VR603 (for play) so that the "PY" mark on the Cam corresponds to the pointer. (d) Repeat above (b) and (c) 2 -- 3 times so that the "S" and "PY" marks on the Cam correspond to the pointer accurately in stop and playback modes respectively. (This adjustment is required because the position adjusted by one volume will be slightly changed when the other volume is adjusted.) (e) Set the N-481 in FF, pause, or record mode by pres sing each switch and check to insure that the pointer is in 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 the Main P.C.B. Note: The value of voltage is typical value.

(a) Observation Point of Reference Voltage Observe the each voltage at the sliding contact of the Cam Control Volume VR601 (10 kohm) in stop, fast (FF or REW), pause, record and playback modes. Note: When Record and Play Switches are pressed to set N-481 in record mode, the Cam is first set to the record position in a short period of time then stays at the play position. Therefore to keep the Cam at the record position, following procedure is required: Short the both leads of capacitor C406 (2.2 uF) on the Main P.C.B. with a jumper wire, then press the Record and Play Switches. (b) Reference Voltage Reference voltage at the sliding contact of VR601 (Cam Control Volume) in each mode is as follows:

(d) Adjustment Procedures

1)

Press the Stop Switch to set the N-481 in stop mode. Adjust the value of R415 and R416 to obtain 15 V (±0.6 V) at the sliding contact of VR601. Note: When R415 and R416 are adjusted, the re-

21

2)

3)

4)

5)

ference voltage in Fast (FF or REW) mode is changed. Therefore, re-check of the reference voltage in Fast (FF or REW) mode is required. If the reference voltage is out of the range, re adjustment of R414 according to next step 2) is necessary. Set the N-481 in FF mode, then adjust the value of R414 so that the voltage of VR601 will become lower by 1.5 V (±0.25 V) than in stop mode. Press the Pause Switch to set the N-481 in pause mode. Adjust the value of R454 to obtain 10 V (+0.4, -0.15 V) at the sliding contact of VR601. Set the N-481 in playback mode, then adjust the value of R453 so that the voltage of VR601 will be come lower by 2.5 V (±0.4 V) than in pause mode. Short the both leads of capacitor C406 with a jumper wire. Set the N-481 in record mode, then adjust the value of R419 so that the voltage of VR601 will become higher by 1 V (+0.4, --0.2 V) than in stop mode. Note: Remove the short of C406 after completion of adjustment.

(3) Cam Timing Adjustment (a) Remove the wires from the Control Motor terminals to set the motor open. (b) Without loading a cassette tape and with pressing the record protecting switch with your finger 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 above step (c) and check to insure that the voltage at the sliding contact of VR601 is 9.5 V (±0.3 V) when mute is released (mute signal changes from H to L). (This voltage is determined by the adjustment of R436 in above step (c).) (e) Observe the (Play + Pause)--Position signal at the Q411 collector. Turn the Cam referring to above step (c) and adjust the value of R432 to obtain 11.2 V (±0.4 V) at the sliding contact of VR601 when (Play + Pause) -- Position signal changes from L to H (bias oscillation will begin). (f) Upon completion of above adjustment, re-connect wires to the motor terminals. 5.2. Tape Speed Adjustment (1) Remove the Top Cover. (2) Connect a Frequency Counter to the Output Jack. (3) Load a 3 kHz Speed Wow/Flutter Tape (DA09006A) and play it back. (4) Referring to Fig. 5.3, adjust the Tape Speed Adjustment Volume (VR501) incorporated in the Capstan Motor to obtain 3,000 Hz on the Frequency Counter. CCW: Motor drives slowly. CW: Motor drives fast.

5.3. Record Head and Playback Head Tilt Adjustment Note: On items 5.3 -- 5.8, please refer to Fig. 5.4 flow chart. Refer to Figs. 5.5 and 5.6. (1) Load a Tilt Check Gauge M-9039 (DA09039A) in the N-481. (2) Clip the grounding terminal of the Tilt Check Gauge with one end of the cord with clip, and the other end to the chassis of the N-481. (3) Remove both of the Height Gears. (4) Set the N-481 in play mode. Check to insure whether the Beacons Playback Head "Upper" or "Lower" and Record Head "Upper" or "Lower" are illuminating. In order not to give damages onto the head surfaces, push both of slide knobs of the Gauge to the direction of arrow marks, then return it to 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 slide knob to the direction of an arrow mark and then return it to the original place. (7) Same procedures will apply to the Beacons Record Head "Upper" and "Lower", except for the height adjustment screw (A). (8) Set the N-481 in stop mode and fit both of the ser rated height gears. Then set the N-481 again in play mode and insure all of the 4 Beacons are illuminating. If not, (3) through (7) will have to be repeated till satisfactory results are obtained.

5.5. Tape Guides Adjustment and Erase Head Stroke Adjustment Remove Head Mount Base Ass'y. Refer to Figs. 5.8 and 59. (1) Supply Tape Guide Height Adjustment (a) Load an EH Stroke Check Gauge M-9042/M-9051 in the N-481. (b) Set the N-481 in play mode. (c) Slide the Supply Tape Guide Check Bar down against the supply tape guide, thus check can be made on supply tape guide height. (d) If the supply tape guide is misaligned, the Supply Tape Guide Check Bar will not come into the supply tape guide. If such is noted, turn to adjust the height adjustment nut A till the Supply Tape Guide Check Bar is accepted by the supply tape guide. (e) If the above are insured, set the N-481 in pause mode, then in play mode to see whether adjustments are appropriately made. If not, (b) through (e) will have to be repeated till satisfactory results are obtained. (2) Take-up Tape Guide Height Adjustment (a) Load an EH Stroke Check Gauge M-9042/M-9051 in the N-481.

(b) Set the N-481 in play mode. (c) Slide the Take-up Tape Guide Check Bar down against the take-up tape 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 adjustments are appropriately made. If not, (b) through (e) will have to be repeated till satisfactory results are obtained. (3) Erase Head Stroke Adjustment (a) Load an EH Stroke Check Gauge M-9042/M-9051 in the N-481. (b) Set the N-481 in play mode, thus check can be made on erase head stroke through the EH Stroke Indicator. (c) Check to insure whether the erase head surface is aligned with red line on the EH Stroke Indicator. If not, adjust the erase head stroke by loosening 2 screws that assembled erase head and erase head plate. (d) After completion of adjustment, 2 pcs. of screws shall be locked with lock tight paint. Note: EH Stroke Check Gauge M-9042 (DA09042A) should be used for the Models from serial Nos. A30601001 to A30604798, and EH Stroke Check Gauge M-9051 (DA09051A) is for the Models bearing serial Nos. A30604799 and greater.

5.6. Erase Head Height and Tilt Adjustment Refer to Figs. 5.10 and 5.11. (1) Remove Head Mount Base Ass'y referring to item 3.22. (2) Load an EH Tilt Check Gauge M-9040 (DA09040A) in the N481. (3) Set the N-481 in stop mode. (4) Check to insure whether one of the 3 Beacons is illuminating. Look down the mirror as shown by an arrow mark and slowly turn the Screw "Height" counterclockwise (or clockwise) so that the two horizontal lines of the mirror will become superposed on the line (in different color) of the erase head, and check to insure whether Beacon "1" is illuminating. (5) Turn Screw "Tilt" counterclockwise (or clockwise) 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" illuminate. (7) Check to insure whether the horizontal line on the mirror corresponds to that on the erase head. If not, (4) through (7) will have to be repeated till satisfactory results are obtained. (8) After completion of adjustment, 3 pcs. of screws shall be locked with lock tight paint Note: Before use of this gauge, check to insure freedom from dust or dirts, or overflow in the groove of the erase head surface.

5.7. Playback Head and Record Head Height Adjustment and Azimuth Alignment Refer to Fig. 5.12. (1) Playback Head Height Adjustment and Azimuth Alignment (a) Connect a VTVM to the Output Jacks. (b) Load a 1 kHz Track Alignment Tape (DA09007A), then set the N-481 in play mode. (c) Turn the PH Height Gear until the output of both channels becomes minimum. (d) Load a 15 kHz Azimuth Tape (DA09004A), then set the N-481 in play mode. (e) Turn the PH Azimuth Alignment Screw until the output of both channels becomes maximum. (f) Repeat (b) through (e) 1 -- 2 times. (2) Record Head Height Adjustment and Azimuth Alignment (a) Connect a VTVM to the Output Jacks. (b) Load a Reference SX Tape (DA09025A). Set the Eq. and Tape Switches of the N-481 to 70 ps and SX positions, then 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 B sides of the tape. (g) Immerse the recorded tape in a magnetized develop ing solution. In turn, check to insure that the recording head tracks across the center are separated with a distance of 0.55 to 0.75 mm (typically 0.65 mm) as illustrated in Fig. 5.13. Note: Liquid for tape magnetized development solution "MAGNA-SEE, SOUND CRAFT a product of CBS RECORDS a division of Columbia Broad casting System, Inc., Danbury, Conn. 06810 U.S.A., or equivalent". After development, clean the tape otherwise pressure rollers and heads will become dirty.

5.8. Record Head Stroke Adjustment Refer to Figs 5.14 and 5.15. Note: This adjustment will be required only to insure freedom from misalignment of the record head stroke in the record head stroke check mode. (1) Check the accuracy of the record head stroke. (2) Remove Head Mount Base Ass'y referring to item 3.22. (3) Remove the record head assembly. (4) Adjustment 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 0.1 mm thickness) between the Block A and Block B, fix the Block A with screws, pushing the Block A to the 2 guide pins. (5) Remove the Block B from the Mounting Gauge Plate. (6) As shown in the Fig. 5.15, mount the R-8L record head assembly onto the Mounting Gauge Plate, then check the location of the R-8L record head surface. (If record head contacts to the Block C, loosen 2 pcs. of screws that assembled record head and R-8L record head assembly, then place the R-8L record head assembly onto the Plate.) (7) Remove the R-8L record head assembly from the Mounting Gauge Plate.

(8)

(9) (10) (11)

(12)

(13) (14) (15)

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, pushing the Block A to the 2 guide pins. Remove the Block B from the Mounting Gauge Plate. Mount the R-8L record head assembly onto the Mounting Gauge Plate. As shown in the Fig. 5.15, loosen the R-8L record head with 2 pcs. of screws onto the record head plate. As the location of the Block A is secured by the item (8) - (c), push the record head to the directions A and B, then tighten 2 pcs. of screws. Check to insure freedom from gap between the Block C and record head surface, then tighten the 2 pcs. of screws on the record head plate with lock tight paint. Assemble the record head assembly to the head mount base assembly. Assemble the head mount base assembly to the mechanism assembly. Check the record head stroke. If the above are inaccurate, items (1) through (15) will have to be repeated till satisfactory results are obtained.

5.9. Tape Travelling Adjustment The adjustment shall be made with a modified version of the current type EXII C-90 as shown in Fig. 5.16 (error will be made if a current type Tape Travelling Cassette (DAO9011A) should be used for this purpose). While modifying an EXII C-90, the tape guides in the cassette housing shall be kept protected to avoid tilt. Check shall be made in the following procedures: (1) An EXll C-90 Tape thus modified shall be loaded onto the N-481. (2) Release the back-tension (rotate the Supply Reel and feed out some length of tape) and set the N-481 in play mode. (3) In this juncture, check to insure whether the tape is free from waving or slippage from the tape guide. (4) When the modified EXII C-90 is played back, check to insure whether the tape is freedom from waving from head surface or at pressure rollers. (5) If either of waving or slippage from the tape guide should be noted, adjustments of "5.3. Record Head and Playback Head Tilt Adjustment", "5.4. Head Base Stroke Adjustment", "5.5. Tape Guides Adjustment and Erase Head Stroke Adjustment", "5.6. Erase Head Height and Tilt Adjustment", "5.7. Playback Head and Record Head Height 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 take-up torque may cause defective tape travelling. The N-481 is intended to be an adjustment-free Model, however if the similar matters as above should be noted, please replace the Reel Hub Ass'y to obtain appropriate

take-up torque. 5.10. Record Switch Linkage Adjustment (1) Set the N-481 in stop mode. (2) Loosen the screw of the Record Spring Holder, and shift the Record Spring Holder in order to remove the looseness of the Linkage Wire as shown in Fig. 5.17.1. Then tighten the screws for fixing the Record Spring Holder. (In this case, the Record Switch should be positioned at play side. If on the record position, it will be defective.) (3) Set the N-481 in record and pause mode. Check to insure that the gap between the top of the wire and the Record Spring Holder is approx. 1 mm as shown in Fig. 5.1 7.2. (Check that the Record Switch is in record position.) (4) Upon completion of the above adjustments, apply a quantity of lock tight paint.

5.11. Flywheel Holder A