Smart-UPS SC 1500 - Under voltage detection, UPS stays on battery power.

[BillP]

Hi all,

I have an old version of APC Smart-UPS SC1500, which was running fine with replaced batteries after not being used for over 3 years.

But just after latest blackout, the UPS just won't go back to normal power from the wall.
After checking it with PowerChute it shows that the battery is running good, self-test passed, and it's charging the battery fine.

The only thing is input voltage is way under and fluctuating between 166 volts up to 204 volts. When it's on 204v it boots up normally, tries to stay on outlet power but keeps failing, when I checked again with PowerChute it shows 192v or less.
I've checked the power outlet and it's on acceptable voltage of 215 volts. 

So, I was wondering if anyone had the same experience and how to solve it.
Does anyone know if there is a component that is failing and might need replacing?

Cheers.