**LG TV Repair Case: After turning on the TV, there is no raster, no sound, and no image.**
**Analysis and Inspection:** First, measure the output voltage of the switch-mode power supply +B (140V), which is approximately 0V. After disconnecting the power, measure the forward and reverse resistance between the +B output terminal and ground, both of which are a few ohms, indicating that there is a short circuit in the load. Upon inspection, it was found that the horizontal output transistor V301 had been damaged due to breakdown. After removing V301, the forward and reverse resistance between the +B output terminal and ground increased significantly. A 100W incandescent lamp was connected in parallel across the +B filter capacitor C670, and the voltage across its terminals was measured at 193V after powering on. This indicates that the reason for the breakdown of the horizontal output transistor was due to an increase in the voltage of the switch-mode power supply. The focus of the inspection should be on the power supply's voltage stabilization control circuit. Upon inspection, it was found that the resistance value of resistor R655 (47 kΩ) had increased to hundreds of kilo-ohms.
**Repair Method:** Replace R655 and V301, and remove the dummy load. The fault is eliminated.
**Inspection Tip:** For this model of TV, it is common for the resistance of R655 to open up, causing the voltage at the +B output terminal of the power supply to rise, leading to the breakdown of the horizontal output transistor. Therefore, when repairing this type of model, it is best to replace the resistor R655 (47kΩ/1/2W) with a 47kΩ/1W resistor for better performance.
**Source of Information:** [http://blog.sina.com.cn/lgdianshiwx](http://blog.sina.com.cn/lgdianshiwx)