Smart UPS 750

[Anonymous user]

Hello everyone,

I have an old UPS giving me some troubles. The batteries inside where really big and "about to explode" so i recycled them and used some i had around to check the ups was working but here the problem: the UPS goes on but all the lights on the panel stays on. No blinking and no buzz. If I connect the unit to the power it starts up and there's ac output. If I start the unit without ac power but only from the battery, I keep pushed the test button then when the buzz starts release it and I get ac output. But why all the lights stays on?

The serial of my unit is: QS0502146199 Model: SUA750I

Thank you

[Anonymous user]

This sounds suspiciously like you have an internal failure in the UPS;  like a damaged inverter/charger (maybe from leaving failed batteries in it too long and it overheated or caused an overload damage on the inverter/charger ) or possibly welded relays. I've had a few ups over the years fail this way, where they turn all the LEDs on at the point of failure. You could , if you have some experience working on electronics, and are careful, check for damage by removing the batteries and let the UPS unplugged and sit to discharge for a couple of days, then remove the covers and check for damage - Eg burned components on the main board.

[Anonymous user]

Hi,

Thanks for your answer. I have some electronics experience and I checked the board, I didn't see any burned component nor smell of burned. At the end the UPS works, just the leds stay all on and that's suspicious.

If it can be helpful I can make high resolutions photos of the internal components and board. Let me know if that would help.

[Anonymous user]

You say the UPS works: so it  does transfer to on and off battery operation properly if you unplug it from the wall with a decent load (say 300 watts) connected,  without shutting down (dropping) the load ?

[Anonymous user]

No sorry, I meant that the UPS output the right AC voltage when in use from the batteries. But indeed, if I disconnect it from the wall plug the UPS shuts completely down, even without load. I hope that that's not the batteries fault, they "look" pretty fit. I took anyway the photos maybe you can tell me something more... Here the link to a Dropbox album: Dropbox - UPS

[Anonymous user]

Well I can't see any visible damage either in the photos.... then its a matter of it could be something invisible, such as a welded relay (one of the three little black rectangular components, and I think one white one) labeled "RY1", "RY2" etc in photos 4 and 5. Usually the ups watches for welded relays during a power on self-test (or during a operation where it has to use them for voltage boost/cut or bypass, etc)...it will shut down and/or turn all the LEDs on / sound an alarm if that is detected, as a safety measure. Or, it could be a damaged micro-controller (the biggish square IC), given how strangely the ups powers up that is a very real possibility.

[Anonymous user]

Thank you.

Do you know if there's any way to test the relay? I know the UPS is old but I want to be sure before throwing it away.

[Anonymous user]

Its a bit laborious, but the relays could be individually tested by unsoldering and removing them from the PC board, connecting an ohm-meter (continuity checker) between their "common terminal" and their "normally open" and "normally closed" terminals, while applying whatever coil voltage is needed across the two coil terminals and see if the continuity flip flops as you apply and remove the coil voltage. The coil voltage might be labeled on the relay, but you may need to go online with the relay part number to determine which terminals are which. Some relays have a single set of contacts (Eg Single Pole Double Throw) and some might have a double set (Double Pole Double Throw)....or more.

[Anonymous user · Accepted solution]

And I guess if the IC is broken then I doubt I will find a replacement...