故障现象:开机后无论用遥控器选台还是手动面板调谐,都收不到任何频段的电视信号,屏幕呈现单一蓝色光栅,但无回扫亮线。检修程序:HFD-2956机在V/U频段内都接收不到电视信号的范围包括主基板上的AV控制电路IC_(1302)、图像中放电路IC_(1301)、中频调谐器U002、高频调谐器U001以及中央微处理器系统中的调谐控制电路。 U001为 PLL数字锁相环频率合成式调谐器(简称FS调谐器)。这种FS调谐系统是在原电压合成调谐(VS调谐)系统的基础上增加一只PLL数字锁相环频率合成电路M549398SP,通过微处理器IC_(101)(CCU—FDTV)三线IM总线进行编程控制,具有频率稳定度高、选台精确、调谐速度快等优点。但作为一 Symptom: Whether you use the remote control or manual panel tuning after power on, you can not receive any frequency band television signal, the screen presents a single blue grating, but no flyback bright line. Maintenance procedures: HFD-2956 machine in the V / U band can not receive television signal range includes the main base of the AV control circuit IC_ (1302), the image discharge circuit IC_ (1301), IF tuner U002, high frequency Tuner U001 and tuning control circuitry in a central microprocessor system. U001 PLL digital PLL frequency synthesizer (referred to as FS tuner). This FS tuning system is based on the original voltage synthesis tuning (VS tuning) system to add a PLL digital PLL frequency synthesis circuit M549398SP, through the microprocessor IC_ (101) (CCU-FDTV) three-wire IM bus programming control , With high frequency stability, channel selection accuracy, tuning speed and so on. But as one