klv-48r472b-no-display-repair
I repaired the Sony KLV-48R452B model, which had a “no display” fault. Initially, when the set was turned on and off repeatedly, the display would sometimes turn on, and after that, it would work perfectly fine, but there was also a fault in the panel. We will share the details of the panel fault separately.
Fault Finding:
After opening the back cover of the set, I first checked the power supply voltages of the main board: VCC 19V, 3.3V, 1.2V, and 1.5V. All the voltages were okay. The backlight was working perfectly, but the display wasn’t showing. I checked the panel’s VCC 12V, and it was missing. When I turned the set on and off repeatedly, the display would turn on, and the panel voltage would appear. When I checked the panel voltage, it was slightly higher than expected, around 12.30V, which made me suspect that the 12V buck converter circuit was disturbed.
I tested the feedback resistors for open circuits, and I found a discrepancy in their values. There was a set of three resistors on the feedback line, which is called a voltage divider. Their function is to supply the IC with a reference voltage. The resistor values are 22K, 120K, and 10K. According to the formula, the value of the 22K resistor was significantly increased. I replaced it, and immediately the panel voltage came back, and the voltage value stabilized at a perfect 12V.
Fault Finding Summary:
The 12V panel regulator IC’s feedback voltage divider resistor (22K) was faulty.
