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User manual NAKAMICHI 481 - SERVICE MANUAL

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Manual abstract: user guide NAKAMICHI 481 - SERVICE MANUAL

Detailed instructions for use are in the User's Guide.

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 1 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 2 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 azi ...
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