I got an old APC Smart UPS 1500VA. UPS could perform only cold start (when I pushed power button over 5 seconds, UPS starts, but running only on battery) .

When i pressed power button, the UPS only beeped shortly and nothing happend. When i connect UPS to the computer and use APC software, I can see that the UPS has detected 230VAC on the power plug. After one hour exploration i was found problem. I don't know why, but it was destroyed transistor Q10.

It was MMBT2222A. After replacing for a new one, everything works. Maybe it helps someone.