Korg SP-250 Service Manual

CONTENTS

• 1) Circuit Diagrams: Page 2 - 6
• 2) Disassembly: Page 7 - 20
• 3) Test Mode: Page 21 - 29
• 4) Parts List: Page 30 - 34

Circuit Diagrams

This section contains detailed circuit diagrams for the Korg SP-250. The diagrams illustrate the electronic components and their interconnections for various boards, including the AMP BOARD, MAIN BOARD, FUNCTION BOARD, and PANEL BOARD. Specific components like ICs (e.g., NJM4580, LA4708, BA3823LS), transistors (e.g., 2SD2114S, DTC114ESA), resistors, capacitors, coils, and connectors are labeled with their respective values and part numbers.

Key boards and their functions are depicted:

• AMP BOARD: Features audio amplification circuits, including power supply regulation (7809, 7805), operational amplifiers (NJM4556A, NJM4580), and power transistors. It includes connectors for outputs, inputs, and speaker connections.
• MAIN BOARD: Houses the central processing unit (CPU), memory, and various control interfaces. It details connections for USB, MIDI, and other peripheral functions.
• PANEL BOARD: Illustrates the control interface, including switches, LEDs, and potentiometers for various functions like tempo, reverb, chorus, and instrument selection (Piano, Organ, Guitar, etc.).
• FUNCTION BOARD: Contains specific functional components related to the instrument's operation.
• PHONES BOARD: Dedicated to the headphone output circuitry.

Disassembly

This section provides instructions for disassembling the Korg SP-250. It details the process of accessing and removing various components and sub-assemblies, including the top cabinet, function board, amp board, main board, and speaker components. Screw types and locations are often indicated in the diagrams.

Test Mode

The SP-250 features a TEST MODE for diagnostic purposes. To enter TEST MODE, the unit should be powered on while simultaneously pressing the [REVERB] and [TRANSPOSE] buttons.

Within TEST MODE, several checks can be performed:

• Internal Check: Verifies MASK ROM and MIDI IN/OUT functionality. The METRONOME LED indicates the status, flashing for OK and stopping for NG.
• Max Output Level / Distortion Ratio Check: Assesses output levels and distortion for OUTPUT, PHONES1, and PHONES2. The METRONOME button is used to cycle through tests. Specific conditions like dummy plugs and 33ohm loading are required.
• Noise Check: Evaluates noise levels for OUTPUT, PHONES1, and PHONES2.
• Speaker Check: Tests speaker output using sine waves at different frequencies (Bass: 120Hz, Treble: 3kHz) in a specific order (Left Bass, Right Bass, Left Treble, Right Treble).
• Keyboard Check: Verifies individual key functionality by pressing keys sequentially from highest to lowest, checking for correct sound output and phase.
• SW & LED Check: Confirms that all LEDs are operational and that switches function correctly, with specific sequences for testing.
• Slide VR Check: Tests the TEMPO VR (volume slider) for smooth movement and sequential LED indication.
• Pedal Check: Verifies pedal functionality by checking LED indicators when the pedal is stepped.
• From Test Mode to Normal Operation: Instructions on how to exit TEST MODE.
• Consumption Currency Measurement: Measures the unit's power consumption.
• Speaker Noise Output Check: Listens for abnormal noises from the speakers with the Master Volume at maximum.
• MIDI Synchronization Check: Confirms proper MIDI communication by connecting the SP-250 to another MIDI unit.
• Demo Performance and Master VR Inspection: Checks the demo song playback, smooth volume control, and potentiometer feel.
• Headphone SW Check: Tests the headphone jack switches to ensure correct sound routing.
• Bad Soldering Check: Involves shaking the unit during demo performance to detect internal soldering issues. A warning is given not to drop the unit from more than 5cm.
• Press Key Check: Evaluates key response to varying velocity (weakly and strongly).
• LINE OUT CHECK: Confirms normal sound output to an external monitor.

Parts List

The document includes comprehensive parts lists, detailing component codes, names, locations on the circuit boards, reference designators, and quantities. These lists cover a wide range of electronic components, mechanical parts, cables, and accessories necessary for the Korg SP-250. The parts are categorized by board (e.g., AMP BOARD, MAIN BOARD, HEADPHONE BOARD) and include items such as:

• Electronic Components: Integrated circuits (ICs), transistors, resistors, capacitors, diodes, coils, ferrite beads, crystals.
• Connectors: Various types of pin headers, jacks, and connectors for internal and external interfaces.
• Switches and Controls: Tact switches, slide potentiometers, knobs, and buttons.
• Mechanical Parts: Cabinets, stands, covers, rubber legs, screws, and mounting hardware.
• Cables: Internal and external wiring harnesses, including ribbon cables and power cords.
• Accessories: Power adapters, owner's manuals.

The parts are also cross-referenced with illustrated parts breakdown diagrams, aiding in identification and replacement.