About this Video

• Video Title: Amplificador Philips 302L. distorsión en un canal
• Channel: Electrónica Antigua
• Speakers: The transcript doesn't provide a speaker's name, only "Hola" at the beginning. It's presumed to be a single speaker.
• Duration: 00:19:46

Introduction

This video documents the repair of a Philips 302L amplifier experiencing distortion in one channel. The speaker systematically investigates the issue, using signal tracing and component testing to identify and replace the faulty parts.

Key Takeaways

• The Philips 302L amplifier is a simple design, both externally and internally.
• The distortion is traced to a faulty integrated circuit (IC) amplifier (STK461).
• Several capacitors and a resistor are also replaced as a preventative measure due to signs of overheating and degradation.
• The repaired amplifier delivers approximately 25 watts of power before signal clipping.
• The video demonstrates the calculation of heat dissipation from the amplifier's heat sink, ensuring adequate cooling.

The video doesn't explicitly state the formula as a single equation. However, the speaker describes the formula's elements: Power to dissipate is equal to the thermal transfer resistance of the material multiplied by the temperature difference between the maximum allowable junction temperature of the component and the ambient temperature. The key variables are: power to dissipate, thermal transfer resistance of the heat sink material, maximum allowable junction temperature of the integrated circuit, and ambient temperature.

The speaker followed these steps to repair the Philips 302L amplifier:

1. Visual Inspection and Initial Assessment: The speaker opened the amplifier and examined its internal components. He noted its simple design and identified the likely location of the problem.

2. Signal Tracing: Using a signal tracer, the speaker tested the signal path to pinpoint where the distortion occurred, tracing it back to the integrated circuit. He confirmed a good signal at the input and output of the integrated circuit, indicating a problem within the IC itself, not just at its connection points.

3. Component Testing (Implied): While not explicitly shown, the speaker’s actions imply testing of other components. He mentions replacing capacitors that might have contributed to distortion, as well as a resistor.

4. Component Replacement: The speaker replaced the faulty STK461 integrated circuit. He also replaced several electrolytic capacitors and a resistor that showed signs of overheating (darkening).

5. Thermal Paste Application: New thermal paste was applied to improve heat transfer between the replacement integrated circuit and its heat sink.

6. Testing and Verification: After reassembly, the speaker tested the amplifier's output with a 150kHz input signal, verifying proper signal amplification in both channels. He then ran the amplifier for a period to allow it to heat up, monitoring for any recurrence of the distortion.

7. Power Output Measurement: The speaker measured the amplifier's output voltage and calculated its power output (approximately 25 watts before clipping).

8. Heat Dissipation Calculation: The speaker calculated the heat sink's ability to dissipate the heat generated by the amplifier using a formula relating power dissipation, thermal resistance, surface area, and temperature difference. He used measurements of the heat sink dimensions to verify its suitability for the amplifier's power output.