Nakamichi BX-300 / BX-300E Discrete Head Cassette Deck

1. General

1.1. Voltage Selector

The voltage selector is installed on the rear panel for versions of the Nakamichi BX-300 other than the standard. This selector allows the user to choose between 120 V or 220-240 V operation.

1.2. Packing Materials and Owner's Manual

2. Test Tapes and Gauges

The following test tapes and gauges are used for adjustments and checks:

1. 400 Hz Level Tape (DA09005B)
2. 1 kHz Track Alignment B Tape (DA09087B)
3. 10 kHz PB Frequency Response Tape (DA09003B)
4. 15 kHz PB Frequency Response Tape (DA09002B)
5. 20 kHz PB Frequency Response Tape (DA09001B)
6. 15 kHz Azimuth Tape (DA09004B)
7. 3 kHz Speed and Wow/Flutter Tape (DA09006C)
8. Tape Travelling Cassette (DA09071A)
9. Reference EXII Tape (DA09066B)
10. Reference SX Tape (DA09025B)
11. Reference SX-E Tape (DA09086A)
12. Reference ZX Tape (DA09037B)
13. EH Tilt Check Gauge S (DA09088A)
14. Stroke Check Gauge S (DA09090A)
15. Tape Guide Height Check Gauge S (DA09091A)
16. Tilt Check Gauge S (DA09039B)

3. Mechanical Adjustment

3.1. Record Head and Playback Head Tilt Adjustment

This procedure involves adjusting the tilt of the record and playback heads using a Tilt Check Gauge S. The process includes removing the pad lifter, loading the gauge, grounding the unit, removing height gears, setting the deck to Play mode, and adjusting height adjustment screws (PH for playback, RH for record) until specific beacons illuminate correctly. The adjustment ensures that both 'Upper' and 'Lower' beacons for each head are lit, and that all four beacons illuminate when the cassette deck is in Play mode after refitting the height gears.

3.2. Head Base Stroke Check

This check requires removing the Cover Plate Ass'y and using a Stroke Check Gauge S. The cassette deck is set to Play mode, and the Record and Playback Head Indicators are moved towards the heads. The adjustment ensures that the 'P' line on the Playback Head Indicator aligns with the central line on the Indicator Plate, and that the 'P' line on the Playback Head Indicator is positioned between the two lines on the Record Head Indicator, verifying the record head stroke.

3.3. Erase Head Stroke Adjustment and Tape Guide Height Check

This section details adjustments for the erase head and tape guides. For erase head stroke, a Tape Guide Height Check Gauge S is used, and the erase head surface is aligned with a red line on the EH Stroke Indicator by adjusting a screw (A) on the erase head plate. For tape guide height, a specific check bar is used to ensure it is accepted by the supply and take-up tape guides.

3.4. Erase Head Height and Tilt Adjustment

This procedure uses an EH Tilt Check Gauge S and involves adjusting 'Height', 'Tilt', and 'Azimuth' screws. The adjustment is performed in Stop mode, observing illuminated beacons on the gauge. The 'Height' screw is adjusted to superpose horizontal lines on a mirror. The 'Tilt' screw is adjusted to light the second beacon, and the 'Azimuth' screw to light the third beacon, ensuring all three beacons illuminate without affecting others. Final checks involve ensuring the horizontal line on the mirror aligns with the erase head surface.

3.5. Playback Head and Record Head Height Adjustment and Azimuth Alignment

Playback Head Height and Azimuth Alignment: Set the Monitor switch to Tape, connect a VTVM to the Output Jacks. Load a 1 kHz Track Alignment Tape and set to Play mode. Adjust the PH Height Gear until outputs of both channels are minimized. Then, load a 15 kHz Azimuth Tape and adjust the PH Azimuth Alignment Screw until outputs of both channels are maximized. Repeat these steps for optimal performance.

Record Head Height and Azimuth Alignment: Set the cassette deck to Stop mode. Set the Monitor switch to Tape, Eq. switch to 70 µs, and Tape Selector to ZX. Load a reference ZX tape and connect a VTVM to the Output Jacks. Feed in 400 Hz (0 dB) to the Input Jacks. Set the deck to Record and Play mode, and adjust the RH Height Gear until outputs of both channels are maximized. Then, feed in 15 kHz (-20 dB) and adjust the RH Azimuth Alignment Screw until outputs of both channels are maximized. Repeat for optimal performance.

3.6. Pressure Adjustment of Take-up Pressure Roller

In Play mode, measure the torque of the Take-up Pressure Roller. It should be within the range of 320 ±50 g-cm. If the torque is outside this range, adjust it by changing the installation point of the Pressure Roller Spring.

3.7. Tape Travelling Check

Load and play a Tape Travelling Cassette. Check that the tape makes sufficient contact with the heads and pressure rollers, that tape waving is minimal, and that the tape moves smoothly without waving or slippage from the tape guides.

3.8. Eject Damper Adjustment

Load a cassette tape. Open the cassette case by pressing the Eject button, then close it manually. Adjust the speed of the damper action using the Adjustment Screw.

3.9. Reel Motor Speed Adjustment in Play Mode

Warm up the deck by playing a C-60 cassette for over four minutes. Load a torque meter (TW-211) and set the deck to Play mode. Adjust VR601 on the Main P.C.B. Ass'y to achieve exactly 50 g-cm on the torque meter.

3.10. Tape Speed Adjustment

Set the Pitch Control Knob to its mechanical center position. Connect a frequency counter to the Output Jacks. Load a 3 kHz Speed and Wow/Flutter Tape and play it back. Adjust VR101 on the Motor P.C.B. Ass'y to obtain 3,000 Hz on the frequency counter. CCW rotation makes the motor drive faster, and CW rotation makes it drive slower.

3.11. Lubrication

The tape transport mechanism is lubrication-free. Apply specified lubricants when replacing the following parts:

• Molykote (R) Grease (X5-6020): Cam Motor Pulley, Thrust portion on the Capstan Shaft
• FLOIL GB-TS-1: Washer between Reel Hub Ass'y and Back Tension Spring
• Diamond Oil (EP56): Reel Hub Shaft
• Anderol 456: Capstan Shaft

Recommended suppliers for these lubricants are Dowcorning Co., Ltd., Kanto Chemicals Co., Ltd., Mitsubishi Oil Co., Ltd., and Toyo Kokusai Oil Co., Ltd.

4. Parts Location for Electrical Adjustment

This section provides diagrams showing the location of components for electrical adjustments on the Main P.C.B. and Meter Amp. P.C.B. These diagrams indicate potentiometers (e.g., VR601 for Reel Motor Speed, VR101-VR104 for Record Level/Peaking, VR105-VR107 for Bias) and other components like filters (L102, L202) and test points.

5. Electrical Adjustments

Electrical adjustments should be performed after mechanical adjustments are complete. The following table outlines the steps, signal sources, output connections, modes, adjustments, and remarks for various calibration procedures.

5.2. Playback Frequency Response Adjustment

Figs. 5.1 and 5.2 illustrate the playback amplifier circuit and the playback equalization curve. This adjustment is necessary if the playback level is insufficient when using a 20 kHz PB frequency response tape. The equalization curve's peaking compensates for playback head gap loss, with the peaking level adjusted by shorting R109 (R209) and/or R110 (R210) on the Main P.C.B. Ass'y.

Diagram Description (Fig. 5.1): Shows a simplified schematic of the playback amplifier circuit with components R109, R110, L101, C105, VR101, R111, and the output stage.

Diagram Description (Fig. 5.2): A graph showing Gain (dB) versus Frequency (Hz) from 100 Hz to 20 kHz. It displays equalization curves for different settings: 70 µs and 120 µs, with variations indicated by shorting or opening of specific components (e.g., ①,② short; ② short; ① short; ①,② open).

8. Schematic Diagrams

8.1. IC Block Diagrams

This section presents block diagrams for various integrated circuits used in the Nakamichi BX-300/BX-300E:

• Fig. 8.1.1: Operational Amplifier IC 4558DD, 072DE, 4556D, 4556C, 2043DD, 082D, TL092. Shows the pin configuration and internal structure of a dual operational amplifier.
• Fig. 8.1.2: OR Gate C-MOS IC µPD4071BC. Depicts the pinout and logic gates for a quad 2-input OR gate.
• Fig. 8.1.3: Exclusive OR Gate C-MOS IC µPD4030BC. Shows the pinout and logic gates for a quad 2-input exclusive OR gate.
• Fig. 8.1.4: Analog Switch Selector TC9145P. Illustrates the block diagram and pinout for an analog switch selector, likely used for signal routing.
• Fig. 8.1.5: Level Meter Driver TA7612AP. Shows the pin configuration and internal structure of a level meter driver IC.
• Fig. 8.1.6: 4-Bit Micro-processor LM6416E-106. A block diagram detailing the internal components such as CPU, RAM, ROM, I/O ports, and timers.
• Fig. 8.1.7: 4-Bit Micro-processor TMP4315BP-1814. Another block diagram for a different microprocessor, showing its architecture and pin functions.

8.2. Schematic Diagrams

This subsection contains detailed schematic diagrams of the Nakamichi BX-300/BX-300E. These diagrams cover the entire circuitry, including power supply, audio processing, control logic, and mechanism control. Warnings regarding component replacement (e.g., 3.5V replacement parts) and cautions for specific voltage settings (120V vs. 220-240V) are provided.

• Fig. 8.2.1.1: Power Switch P.C.B. Assy. Shows different configurations of the power switch PCB for UK (240V), Australia (240V), 220V Class 2 (220V), and Other Versions (120V/220V-240V), including voltage selector and transformer connections.
• Fig. 8.2.1.2: Main Schematic Diagram. A comprehensive circuit diagram illustrating the interconnections of all major components and PCBs.

10. Wiring Diagram

The wiring diagram illustrates the connections between various PCBs and external components. It details the power supply connections for different regions (UK, Australia, 220V, Others, USA/Canada/Japan) via the Power Switch P.C.B. Assy and Power Transformer. It also shows the routing of wires to the Fuse P.C.B. Assy, Control P.C.B. Assy, Counter P.C.B. Assy, Shut-off P.C.B. Assy, and Pitch Control.

Wire Color Codes:

• BRN - Brown
• RED - Red
• ORN - Orange
• YEL - Yellow
• BLK - Black
• BLU - Blue
• VIO - Violet
• GRY - Gray

11. Block Diagrams

11.1. Amplifier Section

This block diagram outlines the signal path within the amplifier section. It shows inputs from the Input VR and Cds, passing through the Input Amp. and MPX Unit. The signal then goes to the Dolby NR Section (Encode/Decode), Rec. Level Calibration, Tape SW IC, Rec. Amp., and Line Amp. The output stage includes Output VR and Meter Amp. The diagram also shows connections for Tape Selector (ZX, SX, EX), Bias Osc., Erase Head, Record Head, Playback Head, and various control signals like Rec. Mute and Line Mute.

11.2. Mechanism Control Section

This block diagram details the mechanism control system. It includes a Counter Controller (with display and buttons like Repeat, Memory, Counter Reset), a Mechanism Control Micro-processor (IC601), and various control circuits for motors and sensors. Key functions managed include motor control (Reel Motor, Control Motor), cam position sensing, eject mechanism, shut-off sensor, and various operational modes (Play, Rec, Pause, Rew, Fwd, Stop). It also shows connections for the DC Power Supply Section and Pitch Controller.

12. Specifications

• Track Configuration: 4 tracks/2-channel stereo
• Heads: 3 (Erase Head x 1, Record Head x 1, Playback Head x 1) <Tape Transport>
• Motors: FG Servo Brushless, Slotless, Coreless, DD Motor (Capstan Drive) x 1, DC Motor (Reel Drive) x 1 <Mechanism> DC Motor (Cam Drive) x 1
• Power Source: 100, 120, 220-240 V AC, 50/60 Hz (according to country of sale)
• Power Consumption: 27 W max.
• Tape Speed: 1-7/8 ips (4.8 cm/sec.) ±0.05%
• Wow and Flutter: Less than 0.048% WTD Peak, Less than 0.027% WTD RMS
• Frequency Response: 20 Hz–20,000 Hz ±3 dB (recording level –20 dB)
• Signal to Noise Ratio: Dolby C-Type NR on <70 µs, ZX tape> Better than 70 dB (400 Hz, 3% THD, IHF A-WTD RMS), Dolby B-Type NR on <70 µs, ZX tape> Better than 64 dB (400 Hz, 3% THD, IHF A-WTD RMS)
• Total Harmonic Distortion: Less than 0.9% (400 Hz, 0 dB, ZX tape), Less than 1.0% (400 Hz, 0 dB, SX, EXII tape)
• Erasure: Better than 60 dB (100 Hz, 0 dB)
• Separation: Better than 60 dB (1 kHz, 0 dB)
• Crosstalk: Better than 60 dB (1 kHz, 0 dB)
• Bias Frequency: 105 kHz
• Input (Line): 50 mV/30 kΩ
• Output (Line): 1.0 V (400 Hz, 0 dB, output level control at max.)/2.2 kΩ
• (Headphones): 5 mW into 8 Ω (400 Hz, 0 dB, output level control at max.)
• Fast Wind Time: Approx. 80 seconds (with C-60 cassette)
• Dimensions: 430 (W) x 100 (H) x 250 (D) millimeters (16-15/16 (W) x 3-15/16 (H) x 9-7/8 (D) inches)
• Approximate Weight: 5.6 kg (12 lb. 6 oz)

Specifications and design are subject to change for further improvement without notice.

Noise Reduction System manufactured under license from Dolby Laboratories Licensing Corporation.

The word "DOLBY" and the Double-D Symbol are trademarks of Dolby Laboratories Licensing Corporation.