UPS TRIPS AFTER 30 SECONDS. I have a Leviton UPS with 6 outlets. Problem is I plug it up (with

Question

I have a Leviton UPS with 6 outlets. Problem is I plug it up (with or without anything plugged in one of the 6 outlets) turn the toggle switch on. Then I get a normal green LED. Within 5 seconds the orange LED flashes about 4 times, then about 10 seconds later the unit trips off. I have checked internal fuses, checked the power cord with ohm meter for a short. Battery is fine, no sign of any thing on pc board getting hot. Anyone have any suggestions?