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故障疑团:开机“三无”,但红灯始终亮。经初诊发现三个问题:(1)+B(115V)对地短路(对地电阻仅为15Ω);(2)遥控(CPU)开/关(待机)功能失效;(3)开关电源无电压输出。三者之间的微妙关系便形成故障疑团。根据以往的检修经验,“三无”(红灯亮),说明电路处于“待机”状态。一般情况是开关电源正常,故障则出在负载或 CPU 开/关机控制电路。因此,检修时往往采用“负载→CPU→开关电源”的顺序。第一次“悬挂”:按照这一检修思路,首先检查了+B(115V)行负载电路,经检查发现+115V 对地电阻仅为15Ω(正常值为3.3kΩ左右),显然是+B 电源负载有短路。检查 D732整流管、C731滤波电容、D731过压保护管、Q602“行管”、C610、C612、C641逆
Suspected of doubt: boot “three no”, but the red light is always on. The first visit found three problems: (1) + B (115V) short to ground (ground resistance of only 15Ω); (2) remote control (CPU) on / Output. The subtle relationship between the three will form a problem suspect. According to the previous maintenance experience, “three no” (red light), indicating that the circuit is in “standby” state. The general situation is that the switching power supply is normal, the fault is out of the load or CPU on / off control circuit. Therefore, maintenance often use the “load → CPU → switching power supply” in the order. The first “suspension”: In accordance with this maintenance idea, first check the + B (115V) line load circuit, the inspection found +15 V resistance to ground is only 15Ω (normal value of about 3.3kΩ), obviously + B power Load short-circuited. Check D732 rectifier, C731 filter capacitor, D731 overvoltage protection tube, Q602 “line control”, C610, C612, C641 inverse