UPS not working

[sagor1]

If the fuses don't pull out, you can still measure across them and see almost 0 ohms across each of them. They may be soldered in....
The fact the battery shows 12.6V alone and when connected to the circuit (powered on) shows the charging circuit in the UPS is not working. Charging voltages should be over 14V

 

[JMaia]

They are soldered. Shouldn't they have 2 legs each? Can I measure using the 2 probes on one leg of the fuse?

 

[sagor1]

Measure across the fuse (2 legs per fuse), one meter probe on each leg. Those fuses seem to be in parallel in the picture, not sure. If there is an open circuit with that check, then both fuses are gone. But, to be sure, check each fuse independently.

 

[JMaia]

Like I Said before, there seems to be only leg per fuse, or maybe its conected by solder. Do I need to desolder them to test

 

[sagor1]

These are the two legs for the two fuses:

 

[JMaia]

oops you're right, I was seeing it wrong, my bad. It reads 01.1 ohms on each fuse.

 

[sagor1]

Fuses are probably ok then. Problem exists elsewhere...

 

[sagor1]

There seems to be something strange about diode D19 (D18?) as in picture, it seems to have burn marks:

 

[JMaia]

You're right, it seems like it melted or exploded. Wich kind of diode should I replace it with?

 

[Diver300]

You're right, it seems like it melted or exploded. Wich kind of diode should I replace it with?

Are there any other diodes on the board that look the same?

Some photos of all the markings would help.

 

[sagor1]

Without a schematic, it will be hard to tell for sure what that diode was. Since the designation is D19, one can assume it is a regular diode of some sort. It could be a 1A diode, or perhaps a 3A diode, depending on the size of it. It might be a fast recovery diode or Schottky diode, which are special purpose. But, without the schematic, one just does not know.
You could replace either a 1A or 3A diode with a standard 3A rated 1N5408 diode, if the leads of the diode fit in the holes ok. If the leads of the 1N5408 are too large, then a 1N4007 diode will fit.

 

[JMaia]

I sent an email to Eurotech asking for the schematic. Here are pics of all the other diodes on the board:

 

[Diver300]

I think that it is the same markings as D9 and D12, and that they are IN400x where x is 0 .. 7. You might as well use IN4007 which has the highest voltage rating.

 

[Nigel Goodwin]

On the left hand picture C40 looks to be swollen.

 

[Lissajous]

Yes, I saw that too. I'd replace it and any others looking tired like that. OTOH, the cap is unlikely to be your root cause fault unless it has failed short. That diode in two parts is far more likely to be your show-stopper! Do check that cap isn't short or replacing the diode might just result in another failed diode.

Good luck getting a schematic. You are usually faster to reverse engineer the circuit and figure component types based on your experience. Manufacturers mostly won't readily supply outside the industry...

 

[JMaia]

I have a few spare diodes, 1N4001 and SR515. Can i use one of these, or should I buy a IN4007?



I googled on how to test the C40 capacitor. Using the multimeter in ohm mode, it displayed some number for a second and then it returned to 1, so I think the capacitor is ok. It is not swollen nor any other capacitor btw, I think it's just the way it looks on the picture.

 

[sagor1]

Both of those diodes may be too low a voltage rating (100 or 150V). The 1N4007 is rated 1000V. What are the markings on the other diodes on the same board, especially those nearby the blown one? That may give a clue as to what you really need.
The only reason to try the 1N4007 is the unknown voltages the UPS is working with, which could be as high as 240VAC or just at the 12V battery voltage. Using something with a higher voltage rating makes it a bit safer to test with. The replacement diode may not fix the issue as whatever caused the diode to pop may still exist in the circuit, like a blown switching transistor.
One step at a time, try the diode first.

 

[JMaia]

I'm unable to read the markings on the other diodes, it's too small. Should I just try and replace the blown diode with a 1N4007 then?

 

[sagor1]

I'm unable to read the markings on the other diodes, it's too small. Should I just try and replace the blown diode with a 1N4007 then?

Yes. See what happens when it powers up afterwards...

 

[JMaia]

Sorry for the late Reply guys, only now i tried to fix the UPS with a 1n4007 diode. I desoldered the old diode and, to test, i put the new one without soldering. When I powered on, everything was working fine. Unfortunately, I tried to solder the new diode and when I powered it on nothing works now, no lights no nothing, i think i ruined the UPS when I soldered the new diode. I tried to take it off and test with another 1n4007 diode (i ordered a few) but nothing changed.