**Source**: Beijing Hisense TV After-sales Service Phone Number, http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3764590.
**Fault Phenomenon**: After turning on the power, the standby indicator light is on, but the entire unit does not work. Using the remote control or the channel button on the panel for a second startup results in the unit working for a few seconds before returning to standby mode.
**Circuit Involved in Fault**: CPU peripheral circuit.
**Fault Location**: Open circuit at R647.
**Methods, Techniques, and Tips**: Control principles and common faults of protection actions in Sanyo A3/A6 chipset TVs.
**Analysis and Repair**: Upon startup, all output voltages from the power supply were measured to be normal, but after a few seconds, the voltage at pin 7 (power control end) of the microprocessor (LC864512V) shifted from a high level (normal operating state) to a low level, placing the unit in standby mode. According to the circuit schematic diagram, analyzed by the Beijing Hisense TV Repair Center, pin 41 of LC864512V is the low-voltage protection detection input terminal. In a normal state, its voltage should be above 4V; if it drops below 3V, the unit enters protection standby mode. The detection signal at pin 41 comes from sampling the 12V, 7.8V, 24V, 180V, as well as the horizontal and vertical pulse signals from the power supply. Upon inspection, it was found that the sampling resistor R647 (390KΩ) for the 180V voltage had an open circuit. This caused the voltage at pin 41 of the CPU to drop to less than 2V through VD642 and R648, prompting the CPU to issue a protection standby command, causing the unit to fail to operate. Replacing R647 resolved the fault.
**★Common Fault**: In Sanyo A3/A6 chipset TVs, an open circuit in the sampling resistor R647 (390kΩ) within the 180V protection circuit causes a malfunction in the protection circuit, which is a common fault.
**Hisense TC-2139 TV No Power-On, Indicator Light On ★**