数字机顶盒维修（Digital set top box maintenance）.docVIP

数字机顶盒维修（Digital set top box maintenance） Digital satellite set-top box practical maintenance technology Author: Yanshou County Radio and Television Bureau of Heilongjiang province Hao Wenjun The basic principle of digital set-top box The digital set-top box is a kind of digital signal into analog signal conversion equipment. The TV station will first analog signal is converted into digital signal (Digital FM signal), digital set-top box transfer home after the digital signal into analog signal input to the analog TV now display information, which can effectively avoid interference and lead to loss of TV signal in the transmission process, the TV signal quality has been greatly improved. Digital set-top box hardware realized by eight functional modules, including QAM tuner, demodulator, MPEG-2 demultiplexing, MPEG-2 decoding, video encoding, audio D/A and user control interface. 1, tuner (the role of high frequency carrier signal frequency selection and frequency reduction): frequency of DVB-C carrier signal above 550MHZ, generating an intermediate frequency signal. The tuner is through IC bus technology to control the channel selection (tuning), the final output signal, no bad signal or weak signal (usually by RF line strong current.). 2, demodulation chip (QAM demodulation and channel decoding):DVB channel encoding using RS+ convolutional interleaving, modulation using 64QAM mode, so the STB must complete QAM demodulation, RS decoding and interleaving (error correction) process, the final output contains MPEG-2 information flow TS. (damaged) bad. 3, CPU chip (MPEG-2 decoding, logic operation, control the user interface) PEC video data and audio data PEC demodulation chip TS output stream contains compression, must PEC data decompression by MPEG-2 decoder. It outputs two sets of signals, a set of digital video signal to digital video encoder, a digital audio signal to the audio group for digital analog conversion PCM format. The screen Huaping bad (non mosaic) and c