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Analysis of repair: Philips MCD988 is a miniature theater, respectively, by the DVD player, amplifier, speakers and subwoofer combination, supporting DTS Digital surround and Dolby Digital surround, Dolby Virtual speaker is able to seamlessly broadcast high quality sound, from a two-speaker system to create a rich and lifelike perfect surround sound effect all over the entire room. The sound structure is shown in Figure 1.MiCservice manual download site
MiCservice manual download site
Main speakers left channel output to normal, indicating a switching power supply circuit, control circuit of MCU and normal DVD player signal processing circuit, and no sound right channel speaker and the subwoofer has no sound, the initial judge faults may appear on the audio amplifier circuit.MiCservice manual download site
Opened the amplifier enclosure, first visually inspect the internal circuit, was not found to be obviously burned out element, has two audio-frequency power amplifier circuit on the circuit board, IC203 (TDA8920BTH) is responsible for the main speakers left and right channel audio signal amplification, a circuit is shown in Figure 2. IC204 (TDA8920BTH) is responsible for the subwoofer audio signal amplification, a circuit is shown in Figure 3. TDA8920BTH is a subsidiary of Philips, a high efficiency class-d digital audio power amplifier IC, HSOP24 flat double row package, with very low power consumption, quiescent current and perfect protection. Pin functions are shown in table 1.MiCservice manual download site
MiCservice manual download site
MiCservice manual download site
MiCservice manual download site
First 500 type retaining main speaker power amplifier integrated multimeter voltage IC203 power supply pin voltage, the amplifier circuit using two sets of positive and negative power supply, ¢Û ¢â voltage +28V, 14, 23 feet, cyclophosphamide, 12, 17, 20 pin voltage -28V, supply voltage is normal. Then with digital oscilloscope detection audio signal of waveform, ¢à, and Krispy Kreme feet left channel audio signal entered waveform normal, 16 feet left channel output waveform also normal, and measuring II, and ¢Ý feet right channel audio signal is no signal entered, continues to to II feet perimeter detection, measuring have resistance R226 (5.6k ω) end has entered waveform, and another end is no waveform, by check, found R226 has virtual welding, right channel audio signal cannot entered zoom, thus led to right channel speakers no voice. Re welded R226, power up test machine, right channel speaker returns to normal.
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