The Kenwood DP-7050 is a compact disc player designed for high-fidelity audio playback, featuring advanced digital signal processing and a user-friendly interface. This service manual provides comprehensive information for its operation, maintenance, and repair.
Function Description
The DP-7050 functions as a digital audio playback device, capable of reading and playing standard compact discs. Its core functionality revolves around a sophisticated digital signal processing chain that includes:
- RF Amplifier (CXA1571S): This IC processes the raw RF signal from the optical pickup, handling 3-spot optical pickup signals, focus error amplification, tracking error amplification, and an Automatic Power Control (APC) circuit for stable laser operation.
- Servo Signal Processor (CXA1372Q): This bipolar IC is crucial for managing various servo controls, including auto asymmetry control, focus OK detection, mirror detection, defect detection and countermeasure, EFM comparison, focus servo control, tracking servo control, and sled servo control. It ensures accurate disc tracking and data retrieval.
- Digital Signal Processor (CXD2500BQ): This LSI (Large Scale Integration) handles all digital signal processing for replay. Key features include a wide frame jitter margin (32K-RAM, ±28 frames), digital PLL for EFM signal strobing (±150kHz capture range), EFM data demodulation, robust error correction (C1: Double correction, C2: Quadruple correction), noise reduction during track jumps, auto zero cross muting, and sub-code Q data demodulation. It also incorporates a digital spindle servo, 16-bit traverse counter, CPU interface via serial bus, built-in servo auto sequencer, digital audio interface output, and a digital level/peak meter.
- Digital Filter (SM5840CP): This 8-times over-sampling digital filter (interpolation) supports 16, 18, or 20-bit input signals and outputs 16, 18, or 20-bit signals, making it a versatile interface. It includes digital de-emphasis (matched to 3fs of 48kHz, 44.1kHz, and 32kHz) and a noise shaping function to reduce re-quantized noises. The filter composition involves three stages of straight-line phase FIR filters and an IIR filter for de-emphasis, ensuring accurate gain and phase characteristics.
- Bitstream Conversion DAC (SAA7350): This 20-bit input CMOS digital-to-analog converter utilizes Philips bitstream conversion technique. It supports various input data formats (I2S, Sony serial, simultaneous idling on LSB/MSB, and simultaneous burst clock) and can be used with the TDA1547 device. It incorporates third-order noise shaping to improve signal-to-noise ratio and prevent idle patterns.
- Bitstream DAC (1-bit) (TDA1547): This dedicated one-bit digital-to-analog converter is designed for high-fidelity sound reproduction. It works in conjunction with the SAA7350, separating noise shaping and one-bit conversion to reduce crosstalk. The TDA1547 is processed in BIMOS, with fully separated left and right channels and supply voltage lines for optimal performance.
- Microprocessor (µPD75216ACW-W35): This central control unit manages all system operations, including user input, display control, and communication with other ICs.
- Power Supply Backup Circuit: This circuit memorizes the ON/OFF status of the secondary power and backs up the IC106 RAM for disc file and the +5V power for the system unit, ensuring data retention even when the primary plug is disconnected.
Important Technical Specifications
The DP-7050 boasts impressive audio specifications:
- Format: Compact disc digital audio system
- Laser: Semiconductor laser
- Number of channels: 2 channels
- Playing rotation: 200rpm~500rpm (CLV)
- D/A Conversion: Twin 1 Bit
- Oversampling: 8fs (352.8kHz)
- Wow & flutter: Unmeasurable Limit
- Frequency response: 4Hz~20kHz, ± 0.5dB (EIAJ)
- Signal to noise ratio: More than 105dB (EIAJ)
- Dynamic range: More than 100dB (EIAJ)
- Total harmonic distortion: Less than 0.001%
- Channel separation: More than 100dB (EIAJ)
- Output level/impedance:
- Fixed: 2V/0.4kΩ
- Variable: 0V~2V/1.1kΩ
- Digital output (Optical): -15dBm~-21dBm (Wave length 660nm)
- Headphone output: 20mW (16Ω)
- Power consumption: 20W
- Dimensions (W x H x D): 440mm (17-5/16") x 127mm (5") x 318mm (12-1/2")
- Weight (Net): 6.8kg (15.0lb)
Usage Features
The DP-7050 offers a range of features for user convenience and control:
- Front Panel Controls: Includes a power key, open/close key, play/pause, stop, search keys, skip keys, display mode key, repeat key, play mode key, numeric keys (0-9, +10), and an output level control knob for adjusting variable and phones jack output levels.
- Indicators: Features a comprehensive set of indicators such as DISC OUT, Program check, Time display, Play track No., Program No., FILE, PEAK SEARCH, EDIT, SPACE, Index No., RANDOM, TIME, PGM, TRACK, STAND BY, EMPHASIS, REPEAT, and A-B REPEAT.
- Remote Control: A full-function remote control unit (A70-0921-05) provides access to all major playback and programming features, including TIME, PGM, TRACK, CLEAR, EDIT, CHECK, RANDOM, POWER, OPEN/CLOSE, PEAK SEARCH, numeric keys, ERASE, SPACE, OUTPUT LEVEL, REPEAT, TIME DISPLAY, and A-B REPEAT.
- Tray Mechanism: The unit features a motorized disc tray for smooth loading and unloading.
- Headphone Jack: A dedicated headphone jack with an output level control allows for private listening.
- Line Out: Both fixed and variable line output options are available for connecting to external audio systems.
- System Control Cord: Allows for integration with other Kenwood components.
Maintenance Features
The service manual details several procedures and considerations for maintenance and repair:
- Disassembly for Repair: Step-by-step instructions are provided for disassembling the unit, including removing the tray panel, disconnecting connectors, removing screws, and detaching the mechanism assembly and PCB board.
- Tray Removal and Mounting: Specific procedures are outlined for safely removing and mounting the disc tray, including setting the pole to fully clockwise and inserting the tray into the chassis guides.
- Pickup Replacement: Instructions for replacing the laser pickup assembly are provided, emphasizing the importance of shorting the short-land of the pickup before procedures and unsoldering it after connecting the flexible wire.
- Test Mode: A dedicated test mode is accessible by short-circuiting specific pins on the microprocessor. This mode allows for functional checks and adjustments, displaying track numbers and enabling various servo functions (focusing, tracking, feed servo).
- Adjustments: Detailed adjustment procedures are given for critical parameters:
- Laser Power: Adjusted to 0.1~0.3mW for an RF level of 1.0Vp-p or more.
- Tracking Error Balance: Adjusted for symmetry between upper and lower waveforms or DC=0±0.05V.
- Focus Error Balance: Adjusted for optimum eye pattern.
- Focus Gain and Tracking Gain: Adjusted to ensure two VTVMs read the same value.
- Circuit Description: Comprehensive block diagrams and pin functions for all major ICs (RF Amplifier, Servo Signal Processor, Digital Signal Processor, Digital Filter, Bitstream DACs, Microprocessor) are provided to aid in troubleshooting and repair.
- PC Board Views: Component side views of the PC boards are included to facilitate component identification and location.
- Exploded Views: Detailed exploded views of both the mechanism and the unit assembly are provided, along with parts lists, to assist in reassembly and part identification.
- Safety Critical Components: The parts list clearly indicates safety-critical components, which must be replaced with specified parts to ensure continued safe operation.
- Regional Variations: The manual notes that component and circuitry may vary by region, providing information on regional circuit modifications and component variations through alternate schematic diagrams and parts lists.
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