Figure 1 shows the installation position of the printed board and components of the GL-891 FM radio, and Figure 2 shows the circuit schematic diagram according to its mapping. The component labels on it are the same as the actual objects. It can be seen from Figure 2 that the FM radio is composed of an integrated circuit of model number 9088 BQ8N. It is a dedicated chip for FM radio with electronic tuning and automatic frequency locking. Its operating voltage is 3V and it is packaged. The form is a plastic package, and the functions of each pin are as follows: {1}, {3}, {6}, {7}, {8}, {9}, {10}, {12} are all external capacitors Terminal; pins {4} and {14} are power input terminals; pins {2} are audio signal output terminals; pins {5} and {16} are frequency modulation signal adjustment terminals; {11} pins are antenna signal input terminals; The {15} foot is the reset terminal. The working principle of the machine is as follows: after closing the switch K, the 3V power supply is filtered by C18 to make the working voltage supplied to the whole machine relatively stable. At this time, the radio wave enters the LC composed of the capacitors C13, C14 and the inductor L2 through the headphone lead The resonant circuit is sent to the {11} pin of the integrated circuit, which is shaped and amplified by the relevant circuit inside it, and then the radio switch is selected through the micro switch SW1. When the circuit captures a strong radio signal, it is automatically locked immediately, and it is converted into an audio signal by its internal circuit, and sent to the adjustable potentiometer VR1 through the {2} pin for volume adjustment, and then coupled to the capacitor C16 The audio amplifier circuit composed of transistors VT1, VT2 and its peripheral components is amplified to drive the headset to work. Capacitors C4 and C17 are used to filter out residual high-frequency signals, and inductive coils L3 and L4 are used to prevent high-frequency signals from entering the headphones to ensure high-quality sound quality. When the channel selection is needed, the frequency modulation signal will be selected from low to high after pressing SW1, and it will be automatically locked. When pressing SW2, the circuit will automatically reset to the lowest frequency.
The faults that are easy to occur during use of this FM radio are mainly the headphone lead broken and there is no sound. The carbon film of the potentiometer is worn and causes noise when adjusting the volume. Generally, it can be restored to normal as long as symptomatic treatment is performed, and the damage rate of the integrated circuit Very low.




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