Doubt is the local press due to leakage. Use alcohol to clean button and blow dried it, boot works fine, about 30 minutes later, the fault appears again.
Drawings of the control circuits, such as native CPU key,-when the control input voltage to represent different commands. Cleaning button, do not press button CPU{39} pin voltage measurement is 4. 15V, press the TV/AV key for 3. 15V, are automatically converted in TV-AV State, indicating there is still residual current in the circuit. Check R2903 resistance was only 8. 05k, press on the icon value is changed to 8. After the 2k, TV work steadily in the ratings, {39} pin voltage when you are not key to 4. 60V, press the TV/AV key for 3. 5V, became AV status.


While working at this time, but CPU{39} pin voltage is still on the low side. Analysis of circuits, there may be external leakage is {39} feet C020, C047, when found C020, sees it as a chip capacitor and taped a small piece of thin copper wires, it seems to cut off the legs of components, which pulled out after logging, {39} feet up to 4. 87V, press the TV/AV key for 3. 68V, is close to normal.
Above maintenance situation, in this case the cause of the failure are: (1) press the leakage; (2) R2903 resistance smaller, (3) C020 beside copper head and cause leakage. Also points out that last button like there is some degree of leakage, but not affect TV work. If the key is not leakage, then when the keys are not pressed R2903 resistance change is CPU{39} pin voltage is not impaired.
Maintenance experience in keying circuit in ladder-shaped resistance, when the instruction when dysfunction should measure CPU keyed input voltage, and then ordinary check-related components and wiring whether there is leakage, and ladder-shaped resistance changed.