How to Repair My Faulty UPS

How to Repair My Faulty UPS

Hello Poultar,

A UPS is very useful in situations where an abrupt power outage may cause data loss on your desktop computer. I understand the desire to repair the device yourself and I hope you get an idea on how to go about doing some simple checks that should more or less prove useful to determine whether the problem is “basic” or not. By meaning “basic” you should be able to do DIY (Do It Yourself) repairs. Let’s proceed.

• You will need some basic tools like a Flat type or Philips screwdriver, an analog or digital multi-meter, long nosed pliers, a soldering iron, desoldering tool, and some soldering lead.

• Examine the UPS and look for disassembly screws usually located at the back. Use your screwdrivers to unscrew covers until you can view the inside.

• Do some preliminary voltage checks using your multi-meter by switching your voltage selector to AC 500V or higher and using the red and black test prods to measure your AC input voltage. Your particular UPS model has a range of 130-300VAC meaning it should function properly within the said low and high limits. Anything lower will cause instability on your UPS. Check your AC line voltage by sticking in both the red and black test prods into your wall socket. 

• CAUTION: make sure your selector is switched to ACV 500 or higher to produce accurate readings. Do not attempt to touch any metallic part of the prod while it is inserted into the wall outlet. Use insulated gloves as a safety precaution. Confirm that the voltage is within 130 to 300 VAC. While still connected, unplug the UPS now and check if the UPS output is within 195 – 245 VAC. Anything lower than 195V is an abnormal condition. Note your readings.

• Now it’s time to do some voltage measurements on the UPS that you just unscrewed. Plug in the UPS, look for red and black wires leading to the 9AH sealed battery. Now switch your multi-meter to DCV 50V or greater. Connect your test prods to the red (+) and black (-) terminals on the battery. Confirm that the reading is +/- 12VDC. Anything less should point to a defective charging circuit.

• If the DC voltage on the battery terminals are normal, let’s check the battery itself. Unplug the UPS, disconnect the red and black connectors leading to the battery (Use a soldering iron if the terminals are soldered) and remove the battery. Now using your screwdriver, short the positive (+) and negative (-) terminals on the battery. CAUTION: A spark might materialize so move back a bit will doing this check. 

• Now measure the voltage reading using your multi-meter set to DC 50V and confirm that the charge is close to +/- 12VDC. Anything less than the value described should point to a dead battery. Another safe check is by using a car battery analyzer to check your battery’s health. Replace if found out to be defective or unable to hold a charge.

• If the battery checks out OK then it’s safe to conclude that the fault lies in the main circuitry for the UPS which could either be a faulty charging circuit, a defective inverter section, or a microcomputer failure at worst.