UPS Repair Help - Dead Units

[kolbep]

Good Day.
I am looking at repairing 2 UPS's for a customer.
They are Identical 1500va units.
Symptoms are the same, that both do not show any signs of life when the batteries and mains are connected. They just act dead.

The 1st UPS had a blown 10A glass fuse next to the heatsink. Replaced the fuse, but it is still dead.
The 2nd UPS's fuse is fine, but also completely dead.

Nothing looks burned/overheated in either of these 12v/230v UPS's

When I hook up the batteries, i get a very small spark, not like the other UPS's I have worked on, when you hook up those batteries, you always jump due to the spark sound....

Anybody experienced with where I can start to look, because I have tried to find any schematic/service manual, but nothing found.

Thanks
Peter

[SeanB]

Power supply? Check the non sanded IC's have power on the pins, they are either standard CMOS or quad opamps. Sanded ones will either be a TL495 or similar SMPS controller or a microcontroller, but once you have the power rails you will see if it has a 5V or 12V supply.  Check the large white ceramic resistors are not open, and check the whole lot of MOSFETS for a short to either DS or DG. They need a start up supply, so if that is not working ( probably because of a dead LM317 or 7812 on the heatsink) then it will sit there and do nothing

[kolbep]

Thanks Sean

It seriously cannot be this easy!!!
From the Battery +ve, it then goes to the ON-OFF-CHARGE rocker switch on the front panel. The power goes there, but does not come back (No matter what position the switches are in).

Bridged out the COM and INV contacts, and it works, Charging, Inverting, everything.
And this is happening on both of them. The rocker switches have both had it. Finally I caught a break with UPS's!!!!

Not too bad considering that I was told by the client that I am the only local Electrician that was willing to even crack the top of the UPS's to see what was wrong.

Now just to order some switches, and (hopefully) get them before the next load shedding session....

[SeanB]

The switches are about R10 each, though I do not think A1 has that small size, just the regular size Defy ones in centre off. You might have to do some file work to get them in there, they probably will be more reliable.

[free_electron]

faulty switches ?  #$%^%&*(  CCC effect . Cheap Chinese Crap

[kolbep]

ACDC has 35 x WS3-3BK in Natal (which is exactly the same size as what I need),
and my dealer has a pickup from them every day,
so I should get them by tomorrow lunch time (well, their lunch time anyway, which is about 3pm!)

The switches are about R10 each, though I do not think A1 has that small size, just the regular size Defy ones in centre off. You might have to do some file work to get them in there, they probably will be more reliable.

[kolbep]

and to think, I washed the board for nothing....
Maybe the other one, I will just blow with a compressor.