My S7 LN randomly shutdowns , sometime after 1 hours ,sometime after 30 min mining, sometime after 6-7 hours

Temperature seems normal, below 63 Centigrade ,both fan are running fine, runs on stock frequency of 600 , all chips seems normal , no faulty chip sign

 What could be the problem ?

devise is 7 days used only and problem starts after day 2 and frequency of random  shut down increased .

in built Power supply can be problem ? So tripping happens

As I need to restart miner by doing jumper switch on-off many time

Please help