After adjustment of this machine use panel key normal voice tone didn't, in strong noise, but all AV status to normal.  6vUservice manual download site
 6vUservice manual download site
First of all, according to the problem described in the fault phenomenon and idea, think this failure should be overall gain to drop, viewing caused by lower sensitivity. Sound is normal, high-frequency head and the back of the audio circuit are normal, as for the users to adjust the machine key after the strong noise, it's wrong or in the user adjust dispatch system chaos caused by, as long as can be properly adjusted again. Panasonic TC - 25 v20r color TV medium frequency signal processing unit circuit as shown in the figure below. 6vUservice manual download site
 6vUservice manual download site
 6vUservice manual download site
First of all, should be carefully check IC101 (4) feet of + 5 v power supply and voltage controlled oscillator (19) foot images of intermediate frequency power supply + 5 v. Whether viewing sensitivity caused by the voltage drop down. Second, the measured power supply under the premise of normal, measuring image of intermediate frequency signal transmission channel triode Q101, Q115, Q117, see whether have put a lot of decrease, leakage, such as potential pitfalls, using the measuring method of tube voltage provide first-hand analysis thought for maintenance. 3 it is under normal operation of the components in Chad, respectively substitution X102 ~ X105 trap, to see whether there is leakage, short circuit to ground will be part of the video signal. Four is the key check IC101 outside RFAGC output circuit element (17) foot C143 and (15) feet high AGC delay adjustment circuit of C115, D202, see if there is leakage or poor performance. Still need to check the B3 plug-in extension and peripheral circuit related plug-ins have because of oxidation and poor contact or by line ask leakage. Fifth, if the above circuit components are no exception, should check IC101 (2), (3) feet external L106 of voltage-controlled oscillation coil, (20), (21) foot external images of the intermediate frequency coil L109 X101 harmony surface. However, according to the maintenance experience, sound surface, it's more see the failure phenomenon is the picture of multiple different length of ious interference. If according to the above method can't be ruled out fault, need to check (10), (11) foot outside?, look to whether feedback abnormal as a result of feedback resistance change value. And check (16) foot external medium frequency AGC filter capacitance C113, look to whether leakage or damage. According to the above steps should be able to eliminate this kind of problems. If not yet, then you can be sure is AN5179AN integrated block damage or bad. After replacement.

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