Eaton (MGE) Evolution UPS repair (help)

[+Mikie]

My first post here and it's asking for help... Doesn't look good, does it?

In any case - I need a bit of assistance fixing this UPS. It does not charge batteries (I've checked). It will run correctly on a charged set until they are drained, at which point starts complaining.

I actually have another working one, and my first suspect was a H-bridge nearest to the batteries with MOSFETS specced for under the mains voltage. They measured differently to the working set, so I changed them, but no joy. I've tried running the supply while opened to measure few things, and I noticed that another single MOSFET is getting fairly hottish and is also not measuring the same as the working one, so I'm waiting for a replacement. We'll see how it goes. Other H-bridge MOSFETs are specced above mains voltage, so I don't think I should be looking there because it outputs the correct voltage. It's just this stupid charging problem.

What is unclear to me is the fairly small transformer that doesn't look like a 600W capable. Upon some searching and reading, I figure that its' the patented MGE high-frequency square wave "modulated" mains, so that would explain smaller size. Higher frequency = higher transformer efficiency.

Anyway - if anyone is willing to have a go at this with me, it would be appreciated. I can provide any number of photos, but unfortunately no schematic. One Perth repair company answered my email with a standard confidentiality drivel, so I didn't bother asking elsewhere. I admire their loyalty to a company that no longer exists, but it is a bit stoopeed.