Yamaha AX-300 Natural Sound Stereo Amplifier
Service Manual
Front Panel
The front panel of the Yamaha AX-300 features controls for Power, Volume, Bass, Treble, Balance, Tape Monitor, and Input Selector. It also includes a Phones jack.
Important Notice
This manual is intended for authorized Yamaha service personnel. It assumes a basic understanding of industry-standard service procedures. Yamaha advises that all service be performed by authorized technicians to avoid personal injury, component damage, or product malfunction. Static discharge precautions should be observed. Ensure the unit is powered OFF during disassembly and parts replacement.
Contents
- To Service Personnel
- Specifications
- Rear Panels
- Internal View
- Disassembly Procedures
- Block Diagram
- Wiring
- Adjustments
- Adjustment Points
- IC Block
- Printed Circuit Board
- Schematic Diagram
- Parts List
To Service Personnel
Critical components are marked with a symbol (A) and must be replaced with parts of identical specifications. Leakage current measurements are required for 120V models to ensure exposed conductive surfaces are properly insulated. The meter impedance should be equivalent to 1500 ohms shunted by 0.15µF. Leakage current must not exceed 0.5mA, and testing should be performed with the AC plug in both polarities.
Specifications
| Parameter | Value |
|---|---|
| Minimum RMS Output Power Per Channel (20Hz~20kHz, 0.05% THD, 8Ω) | 30W |
| DIN Standard Output Power Per Channel (G) (1kHz, 1% THD, 4Ω) | 40W |
| Dynamic Power (A, G, B) (1kHz, 1% THD, 8Ω/4Ω) | 55W/75W |
| IEC Power (G) (1kHz, 0.01% THD, 8Ω) | 35W |
| Power Band Width (0.05% THD, 15W, 8Ω) | 10Hz~50kHz |
| Damping Factor (1kHz, 8Ω) | 40 |
| Input Sensitivity/Impedance (R, U, C) Phono MM | 2.5mV/47kΩ |
| Input Sensitivity/Impedance (R, U, C) CD, AUX, TAPE, TUNER | 150mV/50kΩ |
| Input Sensitivity (New IHF) (R, U, C) Phono MM | 0.47mV |
| Input Sensitivity (New IHF) (R, U, C) CD, AUX, TAPE, TUNER | 28mV |
| Maximum Input Signal (0.02% THD, 1kHz, Phono MM) | 170mV |
| Output Level/Impedance (REC OUT) | 150mV/560Ω |
| Headphone Jack Rated Output/Impedance (0.05% THD, 8Ω) | 0.5V/220Ω |
| Frequency Response (VIDEO-AUX/TAPE/TUNER/CD) (20Hz~20kHz) | +0/-0.5dB |
| RIAA Equalization Deviation (Phono MM RIAA) | ±0.5dB |
| Total Harmonic Distortion (20Hz~20kHz) Phono MM to REC OUT 3V | 0.01% |
| Total Harmonic Distortion (20Hz~20kHz) CD, AUX, TAPE, TUNER/CD to SP OUT 15W/8Ω | 0.01% |
| Intermodulation Distortion (VIDEO-AUX/TAPE/TUNER/CD) (Rated Output/8Ω) | 0.05% |
| Signal to Noise Ratio (IHF-A-Network) Phono MM (5mV Input Shorted) | 88dB |
| Signal to Noise Ratio (IHF-A-Network) VIDEO-AUX/TAPE/TUNER/CD (Shorted) | 100dB |
| Signal to Noise Ratio (New IHF) Phono MM | 74dB |
| Signal to Noise Ratio (New IHF) VIDEO-AUX/TAPE/TUNER/CD | 85dB |
| Residual Noise (IHF-A-Network) | 160μV |
| Channel Separation (Vol. -30dB) Phono MM (Input Shorted 1kHz/10kHz) | 60dB/40dB |
| Channel Separation (Vol. -30dB) VIDEO-AUX/TAPE/TUNER/CD (Input 5.1kΩ Terminated 1kHz/10kHz) | 60dB/40dB |
| Tone Control Characteristics BASS boost/cut | ±10dB (at 20Hz) |
| BASS turnover frequency | 350Hz |
| TREBLE boost/cut | ±10dB (at 20kHz) |
| TREBLE turnover frequency | 3.5kHz |
| Gain Tracking Error (0~-60dB) | 2dB |
| Power Supply (U.S.A. & Canadian models) | AC120V 60Hz |
| Power Supply (European model) | AC220V 50Hz |
| Power Supply (British and Australian models) | AC240V 50Hz |
| Power Supply (General model) | AC110/120/220/240V 60/50Hz |
| Power Consumption (U.S.A. & Canadian models) | 140W |
| Power Consumption (British, Australian, and European models) | 180W |
| Power Consumption (General model) | 120W |
| Dimensions (WxHxD) | 435x92x293mm (17-1/8"x3-5/8"x11-9/16") |
| Weight | 4.6kg |
* Specifications subject to change without notice.
Rear Panels
The rear panels vary depending on the model's region (U.S.A. & Canadian, Australian & British, European & North European, and Others). They feature various input and output terminals, including PHONO, TUNER, VIDEO, AUX, TAPE PB/REC, and SPEAKER outputs. Some models include a voltage selector.
Internal View
An internal view shows the placement of key components such as the Power Transformer, Diode Bridge, Main Circuit Boards, Electrolytic Capacitor, Power Switch, Tape Monitor Switch, Input Selector Switch, Power Transistor, and Radiator.
Disassembly Procedures
The disassembly process involves removing the Top Cover (by unscrewing 4 screws and then 2 more to slide it back), the Front Panel (by removing 5 screws and pulling forward), and the Bottom Cover (by removing 5 screws).
Block Diagram
The block diagram illustrates the signal flow through the amplifier, from various inputs (PHONO, CD, TUNER, AUX/VIDEO, TAPE) through the EQ AMP, IC101, LINE AMP, VOLUME, BASS, TREBLE, BALANCE controls, to the POWER DRIVE stage and finally to the SPEAKER output.
Wiring
Wiring diagrams show the connections between different circuit boards (MAIN 1-7) and external components, including power supply connections, speaker terminals, and input/output jacks.
Adjustments
Idling Current Adjustment: This adjustment is necessary when replacing power and drive transistors. After powering on, allow the unit to age for approximately 5 minutes in a non-loaded condition. Adjustments are made at test points TP1-TP4 using VR105 and VR106 to achieve a rating of 10mV ±3mV DC for both Lch and Rch.
Adjustment Points
Diagrams indicate the locations of adjustment points for Input Selector, Tape Monitor, Balance, Treble, and Bass controls.
IC Block
The IC Block section identifies the AN6557 IC and provides its pin configuration.
Printed Circuit Board
Detailed diagrams of the Printed Circuit Board (Pattern Side and Letter Side) are provided, showing component layouts and connections. Various component values and regional differences are noted.
Schematic Diagram
The schematic diagram provides a comprehensive circuit layout of the amplifier, detailing all components and their interconnections. It includes a legend for component identification (resistors, transistors, capacitors) and notes on component specifications and potential substitutions.
Parts List
Extensive parts lists detail electrical components, mechanism parts, and carbon resistors, including part numbers, descriptions, remarks, and applicable models. This section is crucial for identifying and sourcing replacement parts.
