APC Smart UPS 1500: hiccups

About once a week these 3 year old UPSs (with NEW batteries) cause a computer glitch, apparently during a "self test cycle." Attempts to dukplicate the problem go nowhere. Substituting with a new (cheap) UPS eliminated the problem for over 8 weeks now and counting. I have noticed this condition before with this model and it's prededecessorss.

I suspect one of the (5) Song Chuan (chineese mfg.) relays on the control board has pitted and or bouncing contacts. Replacing all 5 relays on a guess seems like a wast of time and money. Any specific advice? Have you seen or heard of this behavior before?

The lack of a schematic makes this a questionable endeavor, and sending it out for repair of an intermittent condition is almost a guarnteed frustration.