Nakamichi 481, Service Manual

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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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