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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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APC Back-UPS 280B faulty - looking for ideas
I have a APC Back-UPS 280B that has stopped working correctly.
I've had experience in troubleshooting basic electronics and since the layout of this thing is primarly discreet components (only one small IC if I remember correctly), I believe that I might be able to fix it. However, I can't find anything at all about it on APC's website or anywhere else (schematics, user guides, nothing). Symptoms are as follows: In testing it using a 40 watt light as a load, the output voltage across the light is normally about 125 VAC. When the plug is pulled, that voltage drops to about 85 VAC.This was how it was behaving when the problem was first discovered (power outages caused computre to go down), so the internal settings were all as they came from the factory. Initially suspecting the battery, I checked the voltage on the battery in the normal running (i.e., charging) mode. Voltage on the battery was somewhere around 13+ VDC and when the plug was pulled dropped only slightly to somewhere around 12 and 1/2 VDC and held steady. I interpreted this as the battery and the charging circuitry of the 280B were basically good. The setting on the potentiometer for the output voltage of the inverter section was physically set originally at about 2/3 full scale. With a 40watt load and the unit unplugged (output voltage at outlet around 85 VAC), I turned the pot up to full scale. This resulted in the output climbing to around 119 VAC. Although I can (just) get the output up to a "working" level, I would not trust it, it's stability, or load handling since something has obviously gone wrong with it. I do not own or have ready access to a 'scope so I could not examine the output waveform or frequency (I own a Fluke 27 Multimeter) It would be nice to have this working again as I do have an application for it, however: 1) Paying someone to fix it would cost as much as buying another one 2) I can't justify buying another one as I don't have the money for it 3) If it is only a component or cold solder joint that has gone bad, it should be very cheap for me to fix, however: 4) I have no schematics or info on this to help locate where the problem is so I'm a little at a loss, not being familiar with which levels and where to check. If I can't fix this I'm pulling the battery and trashing the UPS which would be shame since I'm sure it is a simple fix once the problem is located. Any assistance, ideas, or even places I could look to find literature on this UPS would be appreciated. Thanks! - Jeff |
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