Chargeing circuit and inverter apc backups
Because the equipment usually protected by a UPS (computers, etc) is sensitive to all kinds of power issues, you'll really want to be able to confirm any repairs you do. If you're not set up for that, it would be much safer to either have APC test and repair it, or if it makes more sense financially, just replace it. Prices have come way down. They haven't reached the level of toasters or VCRs, as far as being "throw-aways," but they're getting close. Just save the batteries.
Assuming it's not still under warranty, you can try fixing it if you have good electronics/electrical training, and the test equipment needed to both troubleshoot AND test it after repairing.
If you have access to the schematics for your unit, that's a major plus. If not, you will have to do a really good visual check, and then have to verify every diode and transistor individually.
Problems with charging circuits usually end up just being a couple of diodes. Inverters blowing up will usually show obvious damage. A good visual inspection of the unit in general, and the transistors on the heat sinks, will typically show obvious damage (transistors burned, or missing chunks). When I was working in the R&D lab for a UPS company, I would always replace all of the transistors on a given heat sink, even if only one tested bad. Your 900va unit probably has four large heatsinks, with 3-4 transistors on each. Make sure you use the same kind of transistors as replacements, unless you have really good info on allowed alternatives from APC. Stats sheets are not good enough, and you might just have it blow again. Also, sometimes the heatsinks are shared by two or more circuits, so a damaged transistor, if unreadable due to damage, might not be the same as the others on the same heat sink. Verify, verify, verify.
May 17, 2015 |
APC Back-UPS® XS 900 (BX900R) UPS System