Konka LCD TV LED32F2000E gray screen fault repair example - appliance repair - Huaqiang electronic network

Filter 18.432M

Konka 32-inch LED32F2000E LCD TV has no picture, no characters, gray screen, remote control and key operation are normal. The initial judgment of the fault is caused by the abnormal operation of the logic board circuit. After disassembling, there is no working voltage input on the power test board 6870C-0414A. After the power is cut off, the inspection work is transferred to the main board 35017303 for maintenance. It was observed that the surface of the upper screen voltage control device V802 on the main board exploded. It is estimated that the rear stage circuit of the V802 has a short circuit. After soldering the V802, test the 8 feet of the V802 to 0 ohms. After unplugging the upper screen line, the test 8 feet are still 0 ohms to the ground. Prove that the logic board should be normal, and the fault is on the motherboard. After checking, it is found that the filter capacitor C864 of the 8-pin output of the V802 is broken down. After replacing 10UF and V802, insert the upper screen line and test the machine OK. (Note: The V802 used in the original machine is a patch 3 foot FET, silk screen WP7N. The model I replaced is the FDS9435 with the 8 pin of the patch, and the soldering copper foil of the two components on the motherboard.)
The following is a schematic diagram of the upper screen voltage control circuit and a simple working principle. After the main chip is working normally, the output PANEL-ON signal (high level), V804 is saturated, and its collector output is low. Thus, the P-channel MOS transistor V802 is turned on, and the 12V voltage is supplied to the T-CON logic board via the S pole and the D pole of the V802.