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According to the above phenomenon to judge the fault in AM radio circuit. The radio part adopts monolithic AM / FM special radio integrated circuit ta8122af (IC5), and the electrically tunable station search, and am radio related circuit shown in the figure. Magnetic antenna T1 induced high frequency signals via a varactor diode (D201, C1, C2 component am input circuit selected to receive radio signals, the first of the field effect tube Q201 for high-frequency amplification, and the capacitor C3 is coupled to the input of ta8122af (IC5) 24 feet (AM antenna input end) am mixing. IC520 T2,, C5, C4 and D202,, AM and IC5, the vibration signal is added to the AM mixer. After mixing from 4 feet output AM IF signal, again by T3, CF2 consisting of 456kHz (the am if the signal is not for ordinary machine 465kHZ) frequency selective circuit selected 456kHz intermediate frequency signal, again from the feet to send internal frequency amplifying circuit. If signal within the IC5 the intermediate frequency amplification, detection, detection of audio signal by 19 feet output, the C6, R1 echo to 18 feet, after being amplified from 13, 14 pin l output, R audio signals to stage amplifier circuit.6sfservice manual download site
Will the machine is arranged on the AM radio status, measuring IC5 pin voltage. It is found that the am if input end and pin voltage is low (normal 2.9v) and unstable, suspect faulty feet that the damage to the internal circuitry or peripheral components. First check the peripheral components, assembly under three terminal ceramic filter CF2, the pin voltage immediately rise as normal 2.9v, thus determining the CF2 is damaged. After the replacement of the new, troubleshooting. If there is no 456kHz if ceramic filter, it can also be used as a common 465kHz of the three terminal ceramic filter emergency.
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