said by lugnut :
Regardless, it serves as a good reminder to everyone to always power down the equipment before attempting any type of service procedure.
Yeah, normally I'm careful about removing all sources of power, but for some reason this time I forgot.
Hopefully it's just the MOSFETs that fried. My preliminary assumption is that the conductive path turned "ON" the gates of the MOSFETs, and since the primary winding of the transformer is a DC short, well, you know the rest.
When I get some time I'll poke around it and figure out the extent of the damage. If it's just the MOSFETs I'll order some new ones and attempt a repair.
said by shortckt:
I have to agree with lugnut there, the fast temp drop caused condensation which provided an arc path, then the flammability of the duster gas expanded on the problem and gave you the fireworks.
Sounds like a plausible explanation.
With regards to the flammability, there were no flames as such, only arcing from the MOSFETs themselves which were completely blown open. The batteries in this UPS are 4x 12V 7Ah in series, so 48V.