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该机VHF频段收看正常,而UHF频段收不到电视节目。从故障现象分析,故障一般在高频头、频段转换开关电路(M54573L)或微处理器(M50436—560SP)等电路中。相关电路如附图所示。工作原理为:在VHF频段搜索时,微处理器第⑥脚电压为0V,第⑦脚电压为5V,经频段转换开关电路后,在其第①、⑦脚输出12V电压,第⑦脚输出0V电压。当
The VHF band watch normal, while the UHF band can not receive television programs. From the failure phenomenon analysis, the fault usually in the tuner, frequency band switch circuit (M54573L) or microprocessor (M50436-560SP) and other circuits. Related circuits as shown in the figure. The working principle is: when searching in the VHF band, the ⑥ pin voltage of the microprocessor is 0V, the voltage of the ⑦ pin is 5V, after the switch circuit of the frequency band is switched, the 12V voltage is output at the first pin and the seventh pin; Voltage. when