Reverse engineering a dell K789N 1920W UPS, any possible help? - Page 1
Forum section: electronics / projects

author: FrisscoCBR
author_rank: Newbie
timestamp: February 06, 2020, 11:50:43 pm
content: I found this UPS in my school lately and tried it, it does not want to turn on, so i ventured inside of it, as literally i could not find any schematics for it nor anything else, i started to reverse engineer it as only way to somehow get it working.I examined the boardand found no burn marks nor blown capacitors or anything else that looks suspicious.On interesting thing is that when i plug it in i hear kind of strange hissing-clicking noise around this red circled region here.So any suggestions?

author: The_Spectrum.A_idiot
author_rank: Regular Contributor
timestamp: February 07, 2020, 12:02:55 am
content: Dear Sir ,I had a UPS that got damaged during a storm , so I presume same thing happened to this too ...so I presume you can try to desolder part by part mesure it and then re-install it ...although no one guranties you you can find what is wrong especially if it has all the strange part numbers(manufacturer specific names) on it that you can't find the original thinga best solution is to follow the path , but these UPS's are "smart" so i guess somewhere it expects the CPU to fulfil some point in order to make it work , although again follow the power and see where it can get youI hope this was helpful ( or you can look on ebay for a good board and call it a day ( if you have good known batteries .. )Thanks

author: FrisscoCBR
author_rank: Newbie
timestamp: February 07, 2020, 12:14:28 am
content: Tnx for reply Spectrum,Well, the strange thing is that workers in school told me that it was almost never used and sat unplugged and untouched for quite some time and it just doesn't work.I found that the problem is most likely in the part where AC comes in and has to be converted to dc, because the main microcontroller (https://www.nxp.com/docs/en/data-sheet/MCF51AC256.pdf) is not getting power at all, nor any point after AC power.So its quite narrowed down but still, so much work to do

author: Gregg
author_rank: Super Contributor
timestamp: February 08, 2020, 02:40:51 am
content: Follow the AC input traces onboard and look for a fuse that may look like a resistor also look for an inrush current limiter. This may get you started in the right direction. For probing about you may want to make a dim bulb tester search the internet for lots of examples.

author: Nattgris
author_rank: Newbie
timestamp: August 09, 2023, 06:47:50 pm
content: I have a UPS of this exact model with precisely the same behavior. Not powering on regardless of whether the batteries are connected or not (they are flat). According to the manual it should power on with just AC power, but give an error message. But display completely dead.Hissing noise from the same region, sounds like a switch mode converter in low load, skip mode. No supply on the control board.Did you ever get anywhere with it?

author: FrisscoCBR
author_rank: Newbie
timestamp: August 18, 2023, 01:50:23 am
content: Actually, you wouldn't believe it. Two days ago I started troubleshooting it again because I need high power UPS like that one. I still didn't fix it but hopefully i will be able to soon enough.Started probing it step by step and checking all the ICs on the board. Two diodes look really suspicious. Just have to find where they go.Will post here as soon as i find something out.

author: kylegp
author_rank: Newbie
timestamp: June 30, 2025, 09:20:30 am
content: I have two of these Dell 1920W models, same board as pictured.One of my units works fine, the other is completely dead. These units don't seem to turn on at all with AC power alone, you NEED working batteries.Even with my working batteries, the faulty unit still doesn't power on. I'd love to know why but no schematics, no burn marks, nothing in thermal camera. I have a feeling it's some switching component but I'm at a loss too.Wonder if you got anywhere with this FrisscoCBR?

author: BradC
author_rank: Super Contributor
timestamp: June 30, 2025, 11:09:36 am
content: You have 2 identical units, one which works and the other that doesn't? Perfect. You can translate measurements from one to the other to figure out where the electrons stop moving.