Observe some channels TV program audio noise, no sound of individual channels and the picture quality is poor, by manual fine-tuning, sound, image can be restored to normal ; Auto Search , lock sets, storage units were normal, poor sound instant channel change subsequent failure to reproduce normally .99Qservice manual download site

    Poor audio channels by hand after trimming may be normal, the fault is not in the sound channel , but the high-frequency tuning inaccurate. The aircraft tuner tuning voltage related to BT and AFT, the corresponding pin voltage monitor tuner found in instant switching channels AFT terminal voltage 4.4V, then at a faster rate dropped to about 0.8V, followed by the sound poor , while BT terminal voltage constant. Therefore, the determination of the AFT circuit fault .99Qservice manual download site
 99Qservice manual download site

    In the synthesis of high-frequency voltage- head remote control color TV , AFT control in general , there are two , one for the CPU according to the AFT amplifier circuit output voltage changes , a corresponding adjustment to its BT -side output voltage to ensure accurate tuning tuner received in the channel . This form does not need to set the tuner circuit terminal AFT , AFT and its tuning functions performed by all BT terminals , AFT amplifier circuit output voltage to the CPU only appropriate port . Another pair of CPU AFT voltage amplifier circuit served only for tuning purposes lock sets , AFT tuner required a separate dedicated control terminal , direct the Central AFT amplifier circuit output voltage control. In this control mode, the station in order to avoid the accuracy of the fill up process AFT voltage change on the lock station , subject located AFT switch. AFT switch off when the station search , tuner AFT terminal plus a fixed voltage ; during normal viewing , AFT switch is turned on , the terminal voltage controlled tuner AFT AFT in the discharge voltage . The machine AFT control the latter .99Qservice manual download site

    Richard machine AFT relevant circuit , see photos. Which IC102 (μPD4066BC) of AFT ON / OFF control , CPU (MN152810ITC3) ⑧ feet AFT ON / OFF control side , 21 feet for the AFT voltage input , medium IC101 (M52034SP) ② feet AFT voltage output. Under normal TV viewing state , AFT function is enabled , CPU ⑧ pin output AFT opened low , IC102 ⑤, ⑥ pin is low, it ⑧, ⑨ feet and ③, ④ feet inside the switches are off , 12 feet high potential , 10, 11 feet inside the switch is turned on . IC101 ② feet AFT output voltage reaches the foot by IC102 11,10 tuner AFT terminals on the implementation of AFT tuner control . When the TV is fill up station status , CPU ⑧ pin output AFT off high , then IC102 ⑤, ⑥ feet high potential, its ⑧, ⑨ foot inside the switch is turned on, the tuner provides a fixed bias by the AFT terminal R1155, R155 voltage. Meanwhile , ③, ④ feet internal switch is also connected, 3,12 pin is low, 10 and 11 feet inside the switch off, disconnect the tuner AFT end and IC101 ② feet between . After the AFT output voltage IC101 ② feet also through Q151 and its peripheral circuit level conversion added to the CPU 21 feet, the CPU voltage as accurate lock station use.

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