Nakamichi-481-tape-sm 维修电路原理图.pdf
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1、 RadioFans.CN 收音机爱 好者资料库 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. Am
2、p. 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 Govern
3、or 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 Lamp P.C.B. L Assy . 17 3. 9. Main P.C.B.Assy . 17 3
4、. 10. Control Switch Holder Assy . 17 3. 11. Switch P.C.B. Assy . 17 3. 12. volume P.C.B. Assy and Control 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 an
5、d 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.
6、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 Adjustment . 24 5. 5. Tape Guides
7、 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 RadioFans.CN 收音机爱 好者资料库 5. 10. Record Switch
8、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
9、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 Switch 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
10、 . 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. Mecha
11、nism Assy 481 (B04) . 44 9. 8. Chassis Assy (B05) . 45 9. 9. Flywheel Holder 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
12、 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. Pneumati
13、c 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 Diagram
14、s . 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
15、 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-hea
16、d contact will result in level drops (c) tape skew will become greater and frequency re- sponse 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. N48
17、1 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 t
18、he 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 fro
19、m 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 stabi
20、lized 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
21、 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 Asse
22、mblies. With a spring in the stud of Mechanism Chassis Assy, Pressure Roller Assy 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
23、 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 a
24、nd 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 align
25、ment 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
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