Through logical analysis, the real part of the fault is not in the memory but in the selection part, you should check the election platform. Because there is no picture of the frequency band voltage or the voltage error of two aspects of the existence of the problem, must first rule out one, to identify the key lies. So should first of all in the normal work of the measured frequency of voltage and tuning voltage and for the record, and then shut down, in a few minutes to boot, when the fault appears measured frequency voltage is normal, but the tuning voltage has dropped 1V, suggesting that from the IC003, foot to vt tuner circuit work unstable components (see chart).

This machine line voltage synthesis method selection and VT formed by the computer to IC003 provide data, by IC003 converted into serial pulse, by foot, output, after r, C035 integral, added to the Q010 inverted amplifier, and the integral circuit to charge and discharge forming sawtooth wave, after electronic filter ripple get smooth DC voltage to control LNB the vibration level of varactor frequency adjustment. Therefore, the average current of Q010C and the pressure drop of the current in the R071 will directly affect the tuning voltage. Now the tuning voltage is only 45 1V, and the current fluctuation is only A, and there is more and more components, so it can not be used to eliminate the fault. If with a heated iron, the iron in the vicinity of the element is heated and the fault temporarily disappear, before long, had a relapse again, still have to rework. In order to ensure the quality of maintenance, the author made the following test and success.

Repair techniques: a good tune radio, measured Q010b C source voltage and R070, R156, r160, R069 resistance at both ends of the voltage, and recorded, shutdown after every few minutes to boot, at fault has been measured Q010C polar voltage drop 0.7V, the rest of the voltage is essentially the same, according to the analysis of the node current law (Kirchhoff's law and Ohm's law shows that the fault coverage in three of elements of a Q010, C037, IC006. According to the principle from easy to difficult and capacitor leakage are most afraid of heating, the first demolition of IC006 and measured is reverse resistance were about 5K and the current flowing through the Ic006 with applied voltage level is no rule changes, to be fixed at both ends of the voltage, the current changes are minimal. Replacement IC006, fault that is excluded.

Cause analysis: as a internal constancy current source integrated voltage regulator tube, IC006. When internal parts are damaged, the current flow through the diode is not stable, resulting in VT voltage instability. In view of the amount of change is small, so when watching a AFT circuit in normal tracking, no escape phenomenon. Each time the conversion channel, the diode two ends of the voltage change, the flow through the current also has no rules to change, resulting in VT is not accurate, so that no image, but the phenomenon appears to be unable to store the program. In this case the logic analysis, find accurate fault location can prescribe the right medicine, Shoudaobingchu. If according to the phenomenon to look at memory, it will "indiscriminately remedies to go a lot of wrong road, even feel unable to start.