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星河XH—800组合音响接收FM广播节目正常,但AM波段收不到电台信号。从该机的电路结构来看,FM收音正常,说明FM与AM收音共用的有关功能开关(AUX、PHONO、TAPE)、音频放大电路均无问题,故障出在μPC1080C集成电路的AM检波及其以前的电路中。参看附图,其故障原因主要有以下几点:(1)AM中放供电端(12)脚无+12V电压输入,致使IC内的AM中放不工作;(2)AM输入调谐回路(16)脚外接的14、VC3电路元件变质或损坏,使IC(16)脚无信号输入;(3)AM振荡回路①脚外接的L5、VC4电路元件变质或损坏,无本振信号送入IC的①脚;(4)(15)、(14)
Galaxia XH-800 combination of FM stereo radio reception program is normal, but the AM band does not receive the radio signal. From the machine’s circuit structure, the FM radio is normal, indicating FM and AM radio shared function switch (AUX, PHONO, TAPE), audio amplifier circuit are no problem, the fault lies in the μPC1080C integrated circuit AM detector and its previous In the circuit. Refer to the attached drawings, the main causes of failure are as follows: (1) There is no +12 V voltage input at the power supply terminal (12) in the AM, causing the AM in the IC not to work; (2) The AM input tuning circuit ) Pin external 14, VC3 circuit components deterioration or damage, so that no signal IC (16) pin input; (3) AM oscillation circuit ① pin external L5, VC4 circuit components deterioration or damage, no local oscillator signal into the IC ① feet; (4) (15), (14)