Nakamichi-481-tape-sm 维修电路原理图.pdf

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. 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 Lamp P.C.B. L Assy . 17 3. 9. Main P.C.B.Assy . 17 3. 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 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 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 RadioFans.CN 收音机爱 好者资料库 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. 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 . 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 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 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 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 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. 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 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 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 5 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. 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 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. 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 6 positioned perfectly vertical to the tape surface. Other-wise, 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 com-mands 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 ex-planation 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. Trig-ger 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. 7 (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. 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: (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 latc