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Old 19th October 2011, 02:56 PM   #1
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Default UPS repair

Has anybody tried to repair a ups for a computer? I have a Belkin FB6-750 that is not functioning.
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Old 20th October 2011, 12:36 AM   #2
Enzo is offline Enzo  United States
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That is not very specific. I have never worked on one, on the other hand I would not hesitate to dive into one if it came to my shop. Circuits are circuits.

A UPS has a battery to store DC power, it has a through connection for the mains power. It has a sensing circuit to detect the absence of mains power. And it has a powr oscillator to make the AC it puts out in place of the mains. It has a power supply for the control circuits. OH, and a charging circuit for the batteries.

SO what is wrong? Are the batteries charged? Bad charger or bad batteries if not.

Does it pass the mains through normally and only fail to make its own mains voltage when power fails? Does it not even do that? Does it make a half-assed attempt at generating mains, but sorta tried? Does it exhibit any signs of life? Is the internal power supply linear or an SMPS?
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Old 20th October 2011, 02:03 AM   #3
ArtG is offline ArtG  United States
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UPSs for computer use come in two flavors. The first is a "true" UPS, that supplies 60Hz 120VAC through an oscillator powered by the battery 100% of the time. The battery is constantly charged from the line, and during a power failure the is no interruption of AC output voltage. The second type, runs off the AC line, but switches (quickly) to battery during a line failure. I suspect you have the second type. I don't know who builds the Belkins, but APC and Tripp-Lite supply most of the smaller backups sold in the US, although there are a number of other companies that build them (mostly larger ones of the first type described).

From my experience, neither APC nor Tripp-Lite make schematic diagrams available, and even if they would, many of them use some proprietary parts, that they don't sell. They don't want you to repair them. I'm sure they want to sell new ones, but there may be a better reason. These are fairly high current devices attached directly to the AC line, and unless one has experience working on this sort of thing, and the proper safety precautions are used, they can present a considerable danger to the technician and possibly to the user. This danger can be present at both the input and output sections of the the UPS, since considerable current at line voltage can be present even with the unit unplugged from the line.

Be very careful!
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Old 21st October 2011, 10:51 AM   #4
dangus is offline dangus  Canada
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Some APC schematics have escaped into the wild. I downloaded a bunch from a website somewhere, maybe Russia. Google apc ups schematics.

I haven't encountered a Belkin UPS, but have looked after a bunch of different APC UPSes ranging from 250 to 1400 VA. The ONLY problems I've encountered were battery failures. Batteries can be deceptive; you may measure 12V or so with a DVM, and it'll look like the UPS inverter fails to start when you disconnect power (or push the test switch). In fact, if you put a static load (like a car headlight or power resistor) on the battery, you'll find that one cell is weak and the voltage immediately drops to 10V. So, when the inverter tries to start, the voltage also dips and an undervoltage detector shuts off the inverter (and latches), and the battery voltage immediately rebounds to the fictitious 12V. You won't catch this voltage dip with a DVM, but it'll be visible with an oscilloscope.

I would avoid the UPSes that use a single 12V 7AH battery; those batteries seemed to fail prematurely, probably because they're worked too hard. The real 450 to 650 VA BackUPS units used either a pair of 6V or a single larger 12V battery, and should survive quite a few years. You can probably get one for next to nothing from a computer recycler and get new batteries from a local industrial supplier. In a pinch, install larger batteries externally.

Last edited by dangus; 21st October 2011 at 10:58 AM.
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Old 21st October 2011, 01:55 PM   #5
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Default ups

My battery was defective so I tried my low amp battery charger. When I turned on the Belkin a steady red light came with Buzzing audio alarm. Belkin says the unit is defective. They no longer make ups's. In order to get a credit on my unit I would have to send it back to them at my own expense. Te cost would be significant. Upon inspection they might issue a credit. I have tried to open unit but cannot get access
to it without destroying it. The unit is 3 years old.
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