Repair case for Skyworth 37K05HR: After booting for about 10 minutes, the screen turns black (no backlight), but the sound is still working properly. The repair was previously attempted elsewhere without success.
Fault analysis:
- The TV boots up normally with no image after 10 minutes.
- Turning it off and on again immediately still results in a black screen for around 10 minutes.
- This behavior suggests a "timed" issue rather than overheating, as overheating would typically cause a shorter delay before failure.
Possible causes include:
- Poor solder joints
- Component instability
- Protection circuit issues
Initial checks confirmed that the power supply voltages (5V, 12V, 24V) were normal, even when the screen was black. However, there was no high-voltage output during the black screen period. This points to an issue with the backlight or high-voltage transformer.
The backlight oscillation circuit uses the STR-H3435 IC. By adjusting the input signal at pin 8 (which controls the pulse frequency), and modifying the reference voltage through the external resistor at pin 8, we can adjust the protection threshold of the IC.
Two possible solutions were considered:
- **Option 1**: Add a 6.8K resistor in series with R25 (currently 33K).
- **Option 2**: Remove R24 (120K).
Only one of these options was implemented in this case. The repair was successful by removing R24 (120K). It's important to note that R25 (33K) and R24 (120K) are connected in parallel.
Below are some photos of the board for reference:
This repair example is for informational purposes only. Always analyze the specific situation before making any modifications.
Biconical Antenna ,Log Periodic Antenna,Marine Vhf Antenna Types
Mianyang Ouxun Information Industry Co., Ltd , https://www.ouxunantenna.com