This phenomenon may be poor or load protection for power supply itself. The first groups of output voltage measurement. Found that the shutdown is caused by IC403 output of 5 v voltage decreases, when the voltage to around 4 v, downtime. 5 v to reduce has two possibilities, one is 5 v power supply failure, another for the heavy load, lead to 5 v was dragged across. After the first replace the 5 v three-terminal voltage regulator IC403, fault is still, but at the same time found IC403 very hot, disconnect the load is still hot. IC403 measurement of the input voltage is about 11 v, the drawing is nominal 7 v. Estimation is IC403 power supply voltage is too high, cause its own fever, over a period of time will not be able to provide a stable 5 v output, automatic shutdown. Dangling IC403 input 1 foot, with an external power input 7 v voltage is added to the 1 foot, after startup, commissioning for long, no longer shut down, their fever not serious, that is the input voltage is too high to cause IC403. Check IC401, IC402, R416 works, finally found the light coupling D408 bad, cause IC403 input voltage on the high side. Change after decoupling D408 normal light.NS6service manual download site