Today, I received a 25-inch assembly machine. The main ICs are: lc863528b, LA76810A, and LA78041. The owner mentioned that two technicians have already looked at it. The problem started with high-voltage ignition, which caused the line to burn out. The first technician replaced the high-voltage package and the line tube, but the issue remained. Then they tried replacing the LA76810 and the field block with the same part, but there was still no improvement.
After taking the unit home, I opened the cover for inspection. I found that the high-voltage package and the line tube had already been replaced with faulty components. When testing the line, it showed a short to ground. I desoldered the C5296 transistor and checked the ground resistance, which was normal. I then replaced it with a D1557, and after checking, there was no obvious short circuit in the line. However, when I turned on the power, I heard a "beep" sound from the high-voltage line, indicating a discharge to the core. After replacing the BSC26-3606A, the field width was only about 10cm, and there was a bright white line in the center of the screen.
I measured the +120V supply and it seemed stable. The large block provided 9V, 5V, and 25V for the field power supply, which all appeared normal. Since both the LA76810 and the field block (LA78041) were newly replaced, I checked the voltages on each pin of the field output. The readings were inconsistent compared to the data sheet. For example, the 3rd pin read 5V instead of the expected 2–2.5V, the 5th pin showed 18V (which should be half the supply voltage), and the 7th pin was at 2.7V (expected around 2V).
I checked the related pins on the bulk and field scan section. Pin 23 (excitation output) was at 2.2V, and pin 24 (sawtooth wave forming end) was at 2V—both within normal range. I suspected the field block might be faulty, so I replaced it, but the issue remained unchanged. After analyzing the circuit diagram, I noticed that the 5th pin's voltage is closely related to the 7th pin. I traced the 7th pin’s connection and found it was connected to the output of the 5V regulator (IC7805) through a 1.8kΩ resistor (R453). I tried replacing R453 with a 2.7kΩ resistor, which improved the situation slightly. The voltage on the 5th pin dropped to 13V, and after adjusting the bus, the screen was fully displayed without any issues.
Wall-Mounted Digital Signage,Wall-Mounted Screen,Hanging Display,Digital Lcd Display
Shenzhen Risingstar Outdoor High Light LCD Co., Ltd , https://www.risingstarlcd.com