DC bus overvoltage fault on SURT10000XLI

[BillP]

at first i brain on (fan on ) the ups.it means after connecting the battery to ups i press the test bottom . the ups fan start to working and i hear a relay sound . after that i apply the AC power (at this moment i should hear the double relay sound ) but i just a one relay sound .after applying the ac power the fault LED (red) turn on. and 3rd LED of battery turn on (i saw the apc manual and i understood it's " DC BUS OVERVOLTAGE FAULT ' . For more info. my OUTPUT outlet socket is faulty but it's not short circuite. i took a pic from my outlet socket. please please tell me which board is faulty ? the PFC or THE INVERTER OR THE Bias board ??? which component ? please please please response fast. thanks thanks thanks aloooooooot .