Hi,


I have here a CyberPowerSystems 1500VA (950W) UPS which has failed in a most peculiar way. Actually, it's not the failure that seems peculiar to me, but that it was ever designed this way to begin with. I've chosen not to move forward with any replacement parts until I can nail down exactly why they are there and what kind of intoxicants the original engineer was on at the time of design.

First off, it doesn't know what model it is. The front says 1500AVR, the sticker in the microcontroller says OP1500 (which is another CPS model), the board says OP2200A (yet another). Ignoring that...

There are two large transformers, completely parallel with each other, each with three windings, two with taps. Of interest is the non-tapped winding, which gives me 24V, and connects back to the main board. It hits first a 6..3A fuse, then a full-wave rectifier (made of discrete diodes), expected filter cap, and then... a mosfet. a 60V 80A n-channel mosfet. Source and drain. The gate goes back to a collection of surface-mount parts which my eyeballs can't seem to follow.

I can't see any reason for this mosfet OTHER than to blow that fuse (which is exactly what it did. the mosfet is failed short).


Anybody have any familiarity with these? I've read that they're not very reliable, they must fail fairly often... so I can't be the only person with a broken one...