Sony TV, after working for more than 10 minutes, experiences image and color drift.
Analysis and Repair: Power off and shut down the machine, wait for it to cool down, then restart. However, the fault reoccurs, leading to the estimation that there is a heat stability issue with a faulty component inside the device. Since the same drift phenomenon occurs in the VHF-L, VHF-H, and UHF bands, it suggests that the faulty component is not in the three independent high-frequency amplification stages or the mixing and local oscillator circuits within the CATV.
This model uses an FS tuning system; the oscillator does not experience frequency drift and does not require AFT voltage for fine-tuning, so the AFT control circuit fault can be ruled out. The fault is suspected to be in the BT voltage power supply circuit at pin 8 of TU101 and the internal frequency synthesizer phase-locked loop circuit. By opening the loop and introducing a 0~30V DC voltage as the tuning voltage, the drift phenomenon no longer appears in the three bands, indicating that the CATV electronic tuner is functioning normally. After disconnecting R103 in the +30V power supply circuit of TU101 pin 8 and monitoring the positive terminal voltage of the filter capacitor C104, it remains stable at +30V, confirming that the fault lies in the internal frequency synthesizer phase-locked loop.
After opening the metal shielding cover of TU101 and monitoring the BT voltage at pin 2, preheating the PLL phase-locked loop section with a hairdryer causes the screen to exhibit the image drift phenomenon earlier, and the image and color drift worsen with rising temperature. The BT voltage at pin 2 of TU101 also deviates more as the temperature increases. Using a magnifying glass, the suspected key components were identified: crystal oscillator X01, Q04 in the LPF circuit, C07, C08, and IC02. Each component was wiped lightly with a small alcohol-soaked cotton ball, repeatedly heated and cooled. When cooling to C07 in the LPF circuit, the cooling and startup time was significantly shortened, determining that C07 was defective.
Case from the Beijing Sony TV After-sales Service Center on September 23, 2011.
Solution: Replacing C07 resolved the fault.