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 Assy ……………………………………………………… 17 3. 2. Top Cover Assy ………………………………………………………… 17 3. 3. Bottom Cover Assy ………………………………………………………… 17 3. 4. Front Panel Assy ………………………………………………………… 17 3. 5. Headphone Jack Assy ………………………………………………………… 17 3. 6. Mechanism Assy …………..……………………………………………………… 17 3. 7. Meter Assy ..………………………………………………………………… 17 3. 8. Lamp P.C.B. R Assy and La mp P.C.B. L Assy …………………………... 17 3. 9. Main P.C.B.Ass y ..……………………………………… ………………………... 17 3. 10. Control Switch Holder Assy .……………………………………………… 17 3. 11. Switch P.C.B. Assy ………………………… ……………………………... 17 3. 12. volume P.C.B. Assy and C ontrol Switch P.C.B. Assy ..………………… 17 3. 13. Rear Panel Assy, Power Transformer and Power Switch ..………………… 17 3. 14. Cassette Case Assy and Cover Plate Assy …………………………… 19 3. 15. Tape CounterAssy ………………………………………………………… 19 3. 16. Capstan Motor Assy and Flywheel Assy ……………………………………… 20 3. 17. Sub Mechanism Chassis Assy ……………………………………………… 20 3. 18. Control Motor Assy and Reel Motor Assy ……………………………………… 20 3. 19. Cam Control volume ………………………………………………………… 20 3. 20. Reel Hub Assy and Idler Assy ……………………………………………... 20 3. 21. Cam Drive Gear and Control Cam ……………………………………… 20 3. 22. Head Mount Base Assy .………………………………………………………… 20 3. 23. Pressure Roller Assy and Erase Head ..…………………………………….. 20 3. 24. Playback Head Assy and Record Head Assy ..…………………………… 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 Ad justment ...……………………………………………… 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 Heig ht Adjustment and Azimuth Alignment 27 5. 8. Record Head Stroke Adjustment .……………………………………………… 28 5. 9. Tape Travelling Adjustment ………………………………………………………… 29 1

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5. 10. Record Switch Linkage Adjustment ………………………………………………\ ………… 29 5. 11. Flywheel Ho lder Adjustment ………………………………………………\ ……………… 30 5. 12. Eject Wire Adjustment ………………………………………………\ ………………………… 30 5. 13. Lubrication ………………………………………………\ …………………………………… 30 6. Parts Location for Electrical Adjustment …………………………………………………………\ 31 7. Electrical Adjust ments 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. Assy ……………….…………………………………………\ …………36 8. 2. Control Swit ch P.C.B. Assy ………………………………………………\ ……………………. 36 8. 3. Switch P.C.B. Assy ………………………………………………\ …………………………. 36 8. 4. Control P.C.B. Assy ………………………………………………\ …………………………. 36 8. 5. Auto Shut-off P.C.B. Assy ………………………………………………\ ……………………. 36 8. 6. Lamp P.C.B. L Assy ………………………………………………\ …………………………. 36 8. 7. Lamp P.C.B. R Assy ………………………………………………\ …………………………. 36 8. 8. Main P.C.B. Assy ………………………………………………\ ………………………………. 37 9. Mechanism Assy and Parts List ………………………………………………\ …………………………. 41 9. 1. Synthesis ………………………………………………\ ……………………………………. 41 9. 2. Front Panel Assy (A01) ………………………………………………\ ……………………. 41 9. 3. Synthesis Mechanism Assy (A02) ………………………………………………\ …………. 41 9. 4. Meter Escutcheon Assy (B01) ………………………………………………\ ………………. 42 9. 5. Control Switch Holder Assy (B02) ………………………………………………\ …………. 43 9. 6. Headphone Jack Assy (B03) ………………………………………………\ ………………. 43 9. 7. Mechanism Assy 481 (B04) ………………………………………………\ ………………. 44 9. 8. Chassis Assy (B05) ………………………………………………\ …………………………. 45 9. 9. Flywheel Ho lder Assy (C01) ………………………………………………\ …………. 45 9. 10. Sub Mechanism Chassis Assy (C02) ………………………………………………\ ……. 46 9. 11. Main Mechanism Chassis Assy (C03) ………………………………………………\ ……. 47 9. 12. Rear Panel Assy (D01) ………………………………………………\ ……………………. 49 9. 13. Reel Motor Assy (E01) ………………………………………………\ ……………………. 50 9. 14. Control Motor Assy (E02) ………………………………………………\ ……………………. 50 9. 15. Head Mount Base Assy (F01) ………………………………………………\ ………………. 50 9. 16. Supply Pressure Roller Assy (F02) ………………………………………………\ …………. 50 9. 17. Take-up Pressure Roller Assy (F03) ………………………………………………\ …………. 50 9. 18. Head Base Assy C (F04) ………………………………………………\ ……………………. 51 9. 19. Cassette Case Holder L Assy (F05) ………………………………………………\ …………. 51 9. 20. Cassette Case Holder R Assy (F06) ………………………………………………\ …………. 51 9. 21. Auto Shut-off Assy (F07) ………………………………………………\ ……………………. 51 9. 22. Pneumatic Damper Assy (F08) ………………………………………………\ ………………. 51 9. 23. P-8L Playback Head Assy (G01) ………………………………………………\ …………. 51 9. 24. R-8L Record Head Assy (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

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11 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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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.

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