Analysis and Repair: Based on the fault symptoms analysis, the common channel of the three frequency bands in the FS tuning system is normal. It can be concluded that there is a fault in the high-frequency amplifier (HFA), local oscillator (LO), and mixer circuits of the VHF-H band. When the fault occurs, the voltage at pin 14 of TU101 for the VHF-H band is measured to be +9V. The voltage at pin 2 (BT) changes normally when switching channels, indicating that the local oscillator for the VHF-H band is basically normal. Gently open the metal shielding cover of T101, and use a magnifying glass to locate the dedicated tuning chip IC025-6, which is the balanced RF input end for the VHF-H band signal and the RF input end of the first gate of the high-frequency amplifier transistor Q02. Observing with an oscilloscope, the RF signal amplitude at both input ends is the same. Measure the DC operating voltage of the drain of the high-frequency MOSFET Q02 and the RFAGC voltage at the second gate, both of which are normal. Open the metal cover of the sub-picture (PIP) FS tuner TU-102, and measure the in-circuit resistance between the first gate, second gate, drain, and source of the internal HFA transistor Q02. These values are completely identical to those of the four terminals of the HFA transistor in TU101. Upon checking the resistive and capacitive components of the VHF-H band HFA stage in TU101, no short circuit or open circuit phenomena were found, and it was determined that the HFA field-effect transistor Q02 is defective.
For the Sony KV-W32MHI1 type TV, the entire unit operates normally when receiving VHF-L and UHF band TV signals, but there is no signal when receiving VHF-H band TV signals.
Solution: After replacing the field-effect transistor Q02, the fault was resolved.
Technical Department of Beijing Sony TV Repair Center, September 28, 2011, bulletin.