Today's repair involves a Sharp 26-inch TV. The issue is that the indicator light is red, and pressing the remote or panel buttons does not make any response. Initially, I suspected a problem with the motherboard. Here are the internal components of the unit:
First, I visually inspected the board for any burnt or damaged components. Nothing obvious was found. Next, I checked the voltages. The 12V and 5V rails were normal, but the 1.2V rail was at 0V. When measuring the input pin of the 1.2V three-terminal IC, it showed only 0.7V instead of the expected 3.4V. This indicated a problem in the voltage regulation circuit.
Following this lead, I traced the circuit and found two 1N4007 diodes connected in series. The voltage before the first diode was 5V, as expected. However, after the diode, the voltage was only 1.5V instead of the expected 4.2V.
After further testing, I confirmed that the diodes were faulty. Replacing them restored the 1.2V rail to 3.4V, and the system started working properly.
The repair was successful, and the TV now functions as intended.
There's also a small tip: if the high-voltage transistor on the flyback is damaged, you can replace it with alternatives like BUZ91, K2645, 10N60, 12N10, K1117, etc.
This kind of repair requires careful testing and attention to detail. It's always best to double-check voltages before assuming a component is bad. Sometimes a simple diode or resistor failure can cause the entire system to fail.
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