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Old 02-19-2019, 09:21 AM   #1
Dannyx
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Unhappy Dell 2700w j728n 3kVa UPS not starting

Good day folks. Another tough one on our hands here I'm afraid, so please bare with my long story: my colleague asked me to have a look at this large DELL UPS which he had set aside for some years after only partly fixing it (from what he told me) before giving up. I have no idea what happened to it or what the original defect was. From what I can see, it must've had some sort of liquid or moisture buildup inside because the boards seem corroded and the insulation has peeled off many of the traces as a result of him cleaning the boards. Some traces even broke off because I can see solder and wires in many places - it's a mess and it's like mission impossible.

Where I currently stand: the battery pack has 97v on it (8x12v cells in series) and when a startup is attempted on battery alone, the DELL logo does appear on the display, I can hear some relay clicks, the fans spin for a while, but it doesn't stay on - it shuts down with no warning or anything after a few seconds and never makes it to the status screen....that's about it. Haven't tested it on mains yet, which is indeed an important test because it should run without the batteries in it and should reveal some hints as to where to troubleshoot, but I don't have one of those fat IEC20 (?) square leads for it yet.

What I found on my own so far: no documentation on this guy, so the closest I got was a similar 3kVA UPS which uses a similar topology and shares some guidelines. There's a PFC circuit, a booster circuit, an inverter circuit (a separate board in this case), a charger board riser module and a "SPS" riser. I can assume for now that the "SPS" riser is fine (NOT pictured yet): this is a small riser board which is a DC-DC converter to step down the 100v straight from the batteries and since (from what I can tell) this is the only path the current from the batteries can take to allow the UPS to come on, even briefly, it's functional.

My next candidate is the booster: takes the battery voltage and with the help of 6 FETs and the transformer, boosts it to 400v - this is not happening: I'm not getting anything at the "BUS" terminals which go to the inverter for further switching. Digging deeper here: I found some wires soldered to the riser board which holds a SG35225a IC (pictured+datasheet) which is responsible for running the FETs. These were soldered to certain pins by my buddy to allow him to measure with the UPS assembled because the inverter board flips up over the main one, making the job impossible otherwise. Pin 15 gets 11v on it as soon as you hit the power button, so it's OK. Pin 10 "SHUTDOWN" however never drops below 4-5v, so this IC is never going to start switching those FETs. In one of my posts about an oscilloscope, I removed this riser and messed around with it on the bench and indeed pulling pin 10 to GND causes it to show some waveforms on pins 11 and 14 (white wires in the pictures) so the IC itself is assumed functional at this point, especially since it's also been replaced at one point, along with the caps as you can see (not my work BTW). Unfortunately this means that the problem could very well be in the uC which may not be sending the "start" command and not assessing that pin LOW either due to an internal defect or some other fault it doesn't like...I shall dig deeper into the main board to at least see where the trace goes exactly - perhaps it's broken or has a series resistor that's gone open (the pull-up one is on the riser itself).

The "computer" riser is the biggest issue: multi-layer, all SMDs, dozens of interconnect pins to the main board...there's no way you're going to fix that at component level....

What do you guys think ? Anyone messed around with large UPSs before ? What would the most common faults be ? Let's at least discuss until I can provide more feedback. I shall return with more photos once I take it apart again.
Attached Images
File Type: jpg 20190219_170115.jpg (825.3 KB, 34 views)
File Type: jpg 20190212_164928.jpg (667.9 KB, 29 views)
File Type: jpg 20190212_164835.jpg (627.4 KB, 19 views)
File Type: jpg 20190212_133419.jpg (688.1 KB, 16 views)
File Type: jpg 20190212_140242.jpg (404.0 KB, 21 views)
File Type: jpg 20190212_164917.jpg (519.2 KB, 15 views)
File Type: jpg 20190212_164804.jpg (748.5 KB, 17 views)
Attached Files
File Type: pdf ST3-1kVA-3kVA-UPS-service-manual-1.pdf (1.30 MB, 20 views)
File Type: pdf SG3525A-D.PDF (142.4 KB, 14 views)
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Old 02-20-2019, 04:26 AM   #2
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Unhappy Re: Dell 2700w j728n 3kVa UPS not starting

UPDATE: plugging the UPS at the wall without batteries in it causes it to turn on and flash the "no battery" icon, so the charger is fine. Fans also spin. I then tried it with the batteries. Upon first plugging it in, the same thing happened: DELL logo came up, status screen appeared and showed 230v in and 0v out, since it was in standby so to say. Held down the power button to attempt a turn-on...big fireworks show, sh!t flying everywhere...it was a disaster and I actually had to take cover Amazingly the display was still running just fine and displaying some error message, despite everything being up in cloud of smoke so if there's one thing that survived is the charge module (the large power-brick riser that I pictured). To the left of that you can also see the small SPS module. The bridge rectifier, IGBT and two diodes are also OK (on the opposite side of the heatsink).

What actually exploded is the 6 FETs for the booster circuit (?) along with their resistors...all history. Trouble is if I replace them (which is expensive to begin with), it could just do it again so I'm not sure what could've caused it. Bad SG35225a ? It also appears to be OK, ironically enough - none of those 4 transistors on its riser board read shorted.

Here's some more pics.
Attached Images
File Type: jpg 20190220_112737.jpg (524.5 KB, 24 views)
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File Type: jpg 20190220_121212.jpg (580.2 KB, 17 views)
File Type: jpg 20190220_121220.jpg (627.9 KB, 18 views)
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Old 02-20-2019, 07:24 AM   #3
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Lightbulb Re: Dell 2700w j728n 3kVa UPS not starting

Here's the service documentation for a similar UPS I was mentioning. It didn't get attached the first time...
Attached Files
File Type: zip Service manual (VGD 700-3K) 20050701.zip (733.4 KB, 40 views)
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Old 02-20-2019, 08:16 PM   #4
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Default Re: Dell 2700w j728n 3kVa UPS not starting

This is why I hate working on other people's "repairs". No idea what the original problem was and no idea what has been done to the unit.

On that note, since this is a Dell unit.... I very seriously doubt those Jianghi 450V, 470 uF capacitors are what this UPS came with. If the originals were replaced, I'd like to know why. If because they were bad, then I'd start right there, because that means something on the booster circuit could have caused them to go bad, like they often do in ATX PSUs. I also wouldn't trust those Jianghi caps to be much good other than for short-term testing.

At this point, with major damage done to some of the switching components, you would have to check every single component in the unit - big or small. No point in continuing, otherwise. Like you said, if you get a pair of new transistors, there's always the likelihood they will blow again, unless you devise a method to current-limit whatever causes them to blow.

In any case, leave the controllers for last - unlikely they are the issue (except for those that may be directly connected to driving power components).
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Old 02-20-2019, 11:54 PM   #5
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Thumbs up Re: Dell 2700w j728n 3kVa UPS not starting

Quote:
Originally Posted by momaka View Post
This is why I hate working on other people's "repairs". No idea what the original problem was and no idea what has been done to the unit.
Correct, though it does give you extra satisfaction if you DO manage to fix it, though that's not why I picked it up originally

I checked just about every component there. I may have exaggerated a bit initially as the damage is not THAT bad. After cleaning up some of the soot from the boards, which made it look like half the board had gone up in flames, it just about started entering the realm of "doable" again. Aside from the 6 FETs which drive that on-board transformer and their 2.2ohm gate resistors, nothing showed immediate signs of failure. The riser I pictured in my first post also appears to have survived: the 4 small driver transistors on it all read identical values (PNP and NPN that is) and so do those SMD resistors. I'll probably replace the IC itself just in case.

Strange that the UPS refused to turn on on batteries but as soon as mains was plugged in THIS happened...I'm saying that because the boost circuit has nothing to do with the mains side - that's handled by a bridge rectifier, an IGBT and 2 diodes on the other side of the heatsink which still measure fine.

Next order of business would be to attempt a power-up just on mains without any of these large components attached at all. By my theory, the unit should still come on and display something since it's got that separate supply which survived. Then, reinstall the 4 components for the PFC circuit: bridge rectifier, IGBT, 2 diodes and attempt another startup without any batteries still. Provided it doesn't hit some error and stop (which it will probably do), that SHOULD get 400v to come up on BUS + and -, to rule out the probability of a bad PFC circuit.

Finally the booster for the batteries: unfortunately we just have to cross our fingers and go for it, since I don't have an adjustable supply that can go that high in voltage. I'll also replace the two blue snubber caps, although don't have any holes punched in them after the incident like I was expecting.

Also, when disassembling it again I noticed that I might have just swapped the + and - leads from BUS going to the inverter by mistake when I put it back together the first time....though that doesn't explain why the FETs blew and not something on the inverter itself...not sure if it really happened or it just seemed so to me...

Last edited by Dannyx; 02-21-2019 at 12:49 AM..
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Old 02-22-2019, 03:39 PM   #6
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Another idea that came to me is that I ran the test with those "probe wires" still attached to the riser with the SG252 and although I covered their ends with electrical tape, maybe it caused some interference on those output pins enough to cause the FETs to latch on...just another theory as to why they blew in the first place...

Today I discovered the input fuse on the charger module also blew, but the major components check out fine still, so I don't know what happened there...

Last edited by Dannyx; 02-22-2019 at 03:42 PM..
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Old 08-25-2020, 05:49 AM   #7
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Hi, bumping this.

Do you know if this model turns on without (or with faulty/discharged) batteries?

I have the Dell UPS 2700R that have been sitting for a couple of years. I only got 34,8V from the batteries (it's 8, so should be 96V), and it will not turn on at all.

So I'm contemplating buying new batteries, but I thought this model turned on regardless (as long as it has landline power), so I don't want to pay ~300USD for nothing. I'm hoping I'm wrong.
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Old 08-25-2020, 05:56 AM   #8
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Default Re: Dell 2700w j728n 3kVa UPS not starting

I didn't come across a fully functional one to confirm, but I know two things:

1) this one DID fire up fine without the batteries, even though it exploded as described later in the discussion when I tried it WITH the batteries on it.

2) the manual talks about an option you can change in the menus (which you probably can't access) which sets if you want it to allow it to turn on without batteries, which by default is on, meaning it SHOULD turn on without batteries indeed...try disconnecting them entirely, instead of trying it with dead batteries on it. Also have a look through the manual in case I'm wrong on this last bit.
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Old 08-25-2020, 07:40 AM   #9
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Thanks for the fast reply!

Not sure if you want me to keep posting here, or make a new thread? This forum seems like a good place to get input on how to get this working?

(I just posted below, and I can edit/move it to a new thread if you would like that).

I can't find any reference regarding powering up without batteries, only that it's possible to power on with only batteries (see below).

Quote:
Starting the UPS on Battery
NOTE: Before using this feature, the UPS must have been powered by utility power with output enabled at least once.
NOTE: Utility power cannot be present at startup.


To start the UPS on battery:
1. Press the button on the UPS front panel until the UPS beeps.
- The UPS front panel display illuminates, and the UPS begins the startup sequence.
- The UPS cycles through Standby mode to Battery mode. The Battery mode icon displays on
- the UPS status summary screen. The UPS supplies power to your equipment.
NOTE: The UPS does not assume the load if you press the button less than three seconds.

2. Press the button to check for active alarms or notices.
Ignore the “UPS on Battery” notice and notices that indicate missing utility power. Resolve other active alarms before continuing. See “Troubleshooting” on page 69. After correcting the alarms, restart if necessary.
You can prevent a battery start (requiring utility power at the next startup) by simultaneously pressing the and buttons for three seconds. Battery start can be disabled. See the Start on Battery setting on page 47.
This UPS worked fine the last time I powered it on (two-three years ago), and have just been sitting at the same spot until we moved a few months ago when (and I finally got a place – and big enough fuse – to run it properly).

So I'm not sure what could have happened to it, except something during the transport and/or batteries? Afaik. it was pretty "well placed" during transport – and it feels like it's built like a brick (and heavy like one too).

As I said, I'm hoping it's the batteries, but I would like to confirm it some way (without buying new ones just to find out it did not work).

On a side note, I did try to measure the voltage from the wires that comes out from the UPS and plug into the batteries, and to my surprise, I got 25,4V (it was not plugged in). Is that normal?

(and I'm way over my head on this one, not really sure what to do)

Last edited by nle; 08-25-2020 at 07:42 AM..
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Old 08-25-2020, 07:50 AM   #10
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Try disconnecting the batteries and power it on without them. If not, it's troubleshooting time, so you may want to start your own thread and leave a link to it here as well since I'd be glad to hear more - at least I'd have a known working one somewhere out there in the world, for comparison if I ever get my hands on mine again
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Old 08-25-2020, 07:52 AM   #11
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Default Re: Dell 2700w j728n 3kVa UPS not starting

I forgot to mention that I did try that – unplugged the battery connection and tried to power it on, but it did not work.

Will make a thread with more details as soon as I have the time.
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Old 08-25-2020, 08:59 AM   #12
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Probably a faulty cap somewhere that died overtime, even with the unit not in use....just my two-cents at this time....
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Old 05-14-2022, 02:17 PM   #13
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Default Re: Dell 2700w j728n 3kVa UPS not starting

And I'm back after two years. I finally had time to have quick look just to confirm that the batteries are all dead. And they are. Not surprising after two additional years just sitting there.

Anyhow, I just thought of something. Do you think it will be possible to hook the UPS up with just one battery for testing purposes?

That way I can get away with buying one battery, and if it works I can buy the rest.
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Old 05-14-2022, 04:44 PM   #14
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Nope, because the batteries aren’t all in parallel. I am thinking it runs at 48V not on 12V.
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Old 05-14-2022, 05:22 PM   #15
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Default Re: Dell 2700w j728n 3kVa UPS not starting

I just checked, and all batteries are connected in series – totaling 8 x 12V = 96V. I attached a photo for reference.

Is there any other easyish way to test to see if it will turn on, without spending money on 8 batteries?
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Old 05-15-2022, 12:26 AM   #16
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Anything that simulates such a large battery voltage is going to be prohibitively expensive.
Have you actually tried to charge each battery separately on a good charger and see what happens?
Because the whole pack will of course not work if one cell is dead...
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Old 05-15-2022, 03:14 AM   #17
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Default Re: Dell 2700w j728n 3kVa UPS not starting

One way of simulating UPS packs I thought of at one point, though this is both dangerous and possibly expensive if you don't have one, is to use a variac with a bridge rectifier. Of course, you wouldn't touch anything or plug the unit into mains at the same time, since it's not isolated and even if it were, I'm not sure what would happen if the UPS tries to push current into the variac to try and charge the "batteries". It should at least give you an idea of whether it runs on batteries or not. Ideally, I'd also use an isolation transformer to make it reasonably safer, though it would still not allow you to feed mains into it for the same reason.

I own a 500va variac myself, but haven't actually been brave enough to try this. One other thing it may not like is the noise on the DC leads, since that DC ain't gonna be the cleanest out there...

Last edited by Dannyx; 05-15-2022 at 03:17 AM..
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Old 05-15-2022, 04:38 AM   #18
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Thanks for the input.

@Per Hansson
I do have a smart 12V 8A (The batteries are 12V 8.5 Ah) charger that I tried on a couple of the batteries. That is throwing an F1 error message right after it tries to assess the battery.

F1 error could be: "Clamps are not secured", "Short circuited" or "reverse polarity". But none of those should be the issue.

My guess is that the batteries are too low for it to do anything, but I'm a bit out of my league on this stuff.

@Dannyx
Thanks for the suggestion, but I don't have a variac, and I think that's waaay out of my comfort zone.
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Old 05-15-2022, 07:46 AM   #19
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Did the batteries looked that cruddy 2 years ago? Just sayin... lots a green... That can't be making good connection.
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Old 05-15-2022, 08:05 AM   #20
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Default Re: Dell 2700w j728n 3kVa UPS not starting

Cruddy? Not sure what you are looking at, maybe the plastic on the connection has a bit of a tint? Anyhow they are more or less pristine. No bad connections there.
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