I have an older UPS that I like a lot, but as I was changing the batteries in it a while back, I accidentally touched the shell of the case with one of the battery leads. Now it won't turn on at all.

Can someone give me some pointers as to how I might repair it, or go about finding what compnent is shot?

I can post pictures of the circuit board, if that would help anyone (although not right now).

Thanks.

I was going to write and tell you some anecdotal tales about a former repair-anything-electronic colleague of mine who instinctively knew never to touch UPSs without specialist repair facilities. Instead, for fear of waffling too much, I'll try and give you a couple of practical tips based upon what he told me

Although they run from 12/24/36 volts and may seem fairly harmless they can be very dangerous.

Wear face & eye protection
The current carrying capacity on the switching side of a UPS is very high so even though it's a relatively low voltage there is a LOT of electrical energy available. If, during your investigations, something goes further wrong there could be a very big bang and you could end up with bits of exploded power transistor and molten metal in your face/eyes.

I know you probably run 110v applicances so this is less of a danger to you than it would be to me (240v); there is almost certainly no automatic shutdown in the event of an accidental earth leakage on the mains side.

Well, I'm always careful around power (okay -- anything bigger than a 9v battery ), which is how it got damaged in the first place, as I was holding a cable waaaay far from the metal bit on the end, it got bendy all of a sudden and slapped down on the case.

Really, I imagine that there is one part in there that's fried, but I don't know what it is. I may just be asking how to check components, but I don't really know.

Returning to the safety aspect again for a moment, and I'm sorry to harp on about this, but I want to make sure I put my prior warning in perspective.....
UPSs deserve a lot more respect than most other electronic appliances. This (now retired) colleague who would never touch UPSs spent his whole working life in the back of TV sets, monitors and so on. 24kv EHT supplies never fazed him one bit.....

Ok, that's me done wittering on about safety

I think pictures of the circuit might be helpful although I'm unsure exactly where that'll lead, maybe nowhere. Right now I'm trying to visualise whether the circuit has flying leads that connect to the battery or whether it's the other way around. And, which one (+'ve or -'ve) was connected while the other shorted against the case?

I've got a really old UPS which I had to replace the entire set of batteries because they had been left discharged for too long. There was a fuse on the PCB which protected the UPS (and you) if for some reason the batteries got shorted out. If you're careful you might want to work out the circuitry attached to the batteries to see if there is a fuse there as well.

- Trevor

Okay, as with others' advice: look for fuses. Almost 100% certain that's what the problem is.

Now.. obligatory UPS story: Everyone in the East remember the ice-storm? I do. I spent several days here sacrificing my Linux hacking to a greater good: I used the UPS to heat the house to a toasy 70F throughout.

Well.. not just the UPS. We have a real wood fireplace, with steel air tubes running in and around the firebox and back out again. With an electric circulating fan, and a nearly airtight door in front (and 20K gold trim..). During the days with no power here, I used our two computer UPS boxes to run the fan periodically. Nice and toasty. Especially in combo with the gas stove, and "primitive" gas water heater (not the fancier high-efficiency kind that needs electrical power).

Cheers!

For a moment there I thought you were going to tell us that UPS' burn with a high calorific output.

The only fuse I can find is the one in line with the main power. I've tested it and it seems okay (unless it's possible that it's marginal and still passes some power but not enough).

I cannot find another fuse on board, but I didn't have as much time to look last night as I'd have liked.

I've replaced batteries in dozens of APC UPSs and have never had any problems. Takes a few minutes and it's done. I see sparks once in a while connecting the red wire up but nothing else.