Repair case for Skyworth 37K05HR: Black screen after 10 minutes of booting, no backlight but sound is normal.
Power board model: 168P-P37ALK-02
This unit was previously repaired elsewhere without success.
Fault description and analysis:
The TV starts up normally with audio, but after about 10 minutes, the screen turns black, although the sound remains fine.
Turning it off and on again immediately still results in a black screen for about 10 minutes, which seems to be "timed."
First, we ruled out overheating as a cause, since that would typically result in shorter operation time.
Possible causes include poor solder joints, unstable components, or issues with the protection circuit.
After opening the cover, all power supplies (5V, 12V, 24V) were found to be normal, whether the screen was on or off.
When the screen is black, there is no high-voltage output, which usually points to an issue with the backlight or the high-voltage transformer.
The backlight oscillation circuit uses the STR-H3435 IC. By adjusting the pulse signal input at pin 8, which determines the core chip's frequency, we can influence the internal voltage comparison threshold.
This allows us to adjust the protection circuit’s behavior.
Two possible solutions:
- Option 1: Add a 6.8K resistor in series with R25 (currently 33K).
- Option 2: Remove R24 (120K).
Only one of these options should be applied.
The repair involved removing R24 (120K), which resolved the issue.
Note: R25 (33K) and R24 (120K) are connected in parallel.
Photos of the relevant parts are attached below for reference.
This case is provided for informational purposes only. Always analyze the specific situation before making any modifications.
Dark gray Transmitting Antenna,B01 Dark gray Receiving Antenna,B01 Dark gray Directional Antenna
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