Damn

Sometimes electronics repairs do not turn out the way you expect

My Dell U2715H monitor has an issue where the screen goes off temporarily the moment some other electrical device is turned on

Sure, the monitor is 10 years old, but it does the job, so why not try to fix it - I thought...

Logically I assumed my U2715H had a power supply problem

So I bought another U2715H off Kleinanzeigen last week in Berlin for €10 that had a LCD problem, assuming I could swap the power supplies and I would be fine

NO! 😡

@jon maybe it's your chair?
https://www.vice.com/en/article/popular-ikea-chair-turns-turns-computer-monitor-off-baffling-everyone/

Swapping the internal power supplies had *absolutely no effect* - same problem

So it must be the main board...

And there there's an issue 😭

Because not all U2715H are the same!

My monitor has a LG made panel, the Kleinanzeigen one a Samsung panel

And the problem: the cabling from the mainboard to the LCD panel is different

So power cable to power supply: SAME
Power supply to mainboard: SAME
Mainboard to LCD panel: DIFFERENT

And as the problem is with the mainboard, I think I am stuck (I need to check the cabling again to be sure, but the LCD panel end of the cabling is definitely different)

So what is it that I am turning on that causes the issue?

Anything with a transformer, and particularly my JBL Creature speakers that have a large fat transformer

So that is creating inrush current when I turn it on, and the fragile mainboard in the U2715H cannot cope, and - for a few seconds - it goes off

@jon I have the same problem with a relatively new monitor at home (HP) and at work (Dell). It's probably due to a missing or incorrectly grounded connection.

@jon Ooh that's frustrating. Nice monitor though.

It's probably not the issue but just for that 1% chance that it is: a grounding issue has the same symptoms. Small power jolts or even static electricity (chair or desk on certain flooring, clothes, dry air) causing resets.

My fairly new monitor connected to a high quality USB hub randomly does this as well. There's absolutely nothing wrong with it and the issue went away when I brought the combo to an office for a week.

@zhenech @jon oh that's interesting... I've got that chair, and one of my 4k monitors keeps "dropping out"!

@richlucking @jon it's not limited to that particular chair AFAIK

BUT if I connect the monitor that I bought on Kleinanzeigen, that does not suffer in the same way - it stays on

So I have one U2715H with a fragile mainboard, and a working LCD panel

And another U2715H with working mainboard, but a damaged LCD

And I cannot switch them because of the incompatible cables 😭 😭 😭 😭

@jon Is the PSU all tiny parts or can you stick more caps on it and perhaps a ferrite ring on the input in case its inteference driven ?

@jon Disappointing for a Dell. Especially for something that could be fixed with a penny worth of capacitors.

Could you run the monitor alone off a spike-protected extension?

@jon

Just a guess. Check large electrolytic capacitors. If any of them look swollen or show signs of leaking, replace them.

That might fix it.

The only way, really, to eliminate the issue would be to run the monitor on one circuit in the house, and all my other devices on another circuit, but based on where everything is located in the house I cannot do that...

Anyway, lessons learned:
- Inrush current seems to have an impact
- Not all Dell U2715H monitors are the same inside!

/ends

P.S. @Pepijn wondered if it was a problem with the grounding

I have tried with both devices on another circuit in another part of the house that has more modern wiring, and I get precisely the same issue

Only putting the Dell on one circuit, and the JBL speakers on another, eliminates the issue - but that puts one of them somewhere I do not work! 😄

@oschonrock See the whole thread.

It is something on the mainboard, and there I do not have the skill to replace them.

@jon

Yeah, I meant on the main board, but modern electronics are harder to work on without specialised tools and skills.

Shame, was a good idea / instinct.

@etchedpixels It's not interference - it is caused by anything with a transformer that is on the same circuit. Putting the speakers in another room on the same circuit causes the same issue. It seems to be the inrush current to the transformer leaves the Dell monitor with a shortage, momentarily, and that knocks it off for some seconds.

@jon Yup. Sounds like you ruled that out then. Too bad.

Just in case you have one laying around.. A voltage regulating UPS can work as a "buffer" dampening the inrush. It's a waste of energy and equipment if you'd have to purchase one just for this reason though.

@oschonrock Yes, but I think my best bet is simply finding another broken monitor that has the type of mainboard I need! 🙂 Or trying to find a suitable cable.

@Pepijn Sadly my only UPS is a 12v one for the internet router. I do not have a 240v one.

Very easy bet that there's a blown capacitor on the board. Good news is that blown capacitors are extremely easy to recognize (they're ballooned or even lost their head cap) and one of the easiest electronics components to replace. 2 minute job, especially if you have a friend used to a soldering iron.
@jon

@osma I will open it up again and check that. But tomorrow 🙂

@jon Just as an aside, I had a set of JBL Creatures and the sound quality was piss-poor. You'd do much better with a budget hi-fi amp and old-school speakers. Cheaper, too, from most charity shops.

@jon @Pepijn would it possible to set up a voltage smoothing adaptor (homemade?) between the mains and the monitor (something with a big capacitor should do it), effectively your own several seconds UPS.

@cstross Then you somehow got a bad set, because the sound from these speakers is just fine, and I have owned them for years.

I have two impeccable quality hifi systems in the house as well, but not where my desk is.

@UkeleleEric @Pepijn It's not serious enough to go to that effort. It'd be easier to find a suitable replacement cable for inside the monitor! 🙂

@jon @UkeleleEric @Pepijn you can buy plug in surge suppressors and/or frequency filters.

@jon @UkeleleEric @Pepijn it can also be a bad video cable picking up electrical weirdness.

@jon maybe try: does it only blank out when hdmi or dp is connected? Might be the shielding of the cable picking up the pulse from the other devices.

@jon Would a surge suppressor possibly help? You can/could find power boards with those built in

@jon Have you tried connecting your display to your computer with a different data cable? So different HDMI or DisplayPort cable, or perhaps switch to a different port (type) as well.
Poor shielding on the data cable, or a sensitive protocol handling chip can be a much bigger problem than even substantial EM surges on the power connection.

@timo tried that. Same regardless of what’s connected.

@pmdj Yes. Makes no difference.

@timo it also cuts if nothing is connected.

@jon That is interesting. It potentially explains why I have two Dell monitors of the same model on my desk at work that behave differently on my Mac.

@rainynight65 that’s a possible explanation indeed. There are some Rev numbers on these on the back - maybe from that you can deduce what’s inside?

@jon I'll have a look next time I'm in the office. It's not a major issue, it was just puzzling to see why, in the display settings, one monitor would let me select a specific resolution while the other conforms to the MacOS display settings ('bigger text' or 'more space').

@jon I had the same problem with so many different PC screens and TVs at six different apartments in two very different countries.
I thought this is just something people are expected to live with.

@Pepijn @jon Another possibility could be high-frequency noise / EMI spikes messing up the digital data flow (cf. “my monitor turns off every time I stand up/sit down onto my gas-lift office chair”, https://www.reddit.com/r/techsupport/comments/2rsivw/monitor_shuts_off_briefly_when_i_stand_up_from_my/), in which case ferrites may be your friend.

Have you tried running a non-challenging display mode (resolution & refresh) to see whether it still happens then? Those display signals are more EMI-robust.

@happydisciple @Pepijn Nope, no difference. Different cables, different locations, people moving or not - all makes no difference. The thing that consistently does is turning on devices that have transformers that are on the same ring main.

@linjari Tested that one. That's not the case here. Same however I cable it, and I have used alternative HDMI and alternative power cables.

Follow up: so I opened the monitor up again

The mainboard in my Dell U2715H has plugs to the LCD as shown in Pic 1. Different to the plugs on the mainboard of the Kleinanzeigen one, Pic 2. So the mainboard to LCD cables are different on *both ends*

So for now I am back to using a backup Samsung 1080p monitor (Pic 3) until I have assessed what to do!

Oh and @osma suggested I check for damaged capacitors - none to be found (not obvious anyway)

@jon @osma Did you try baking the PCB in an oven to reflow any potentially loose or broken solder?

@jmovs @osma No I am not going to do that, because I might damage it further. After all I can live with the fault if I have to!

@jon @jmovs @osma Have you tried reversing the polarity of the EPS conduit, or recalibrating the flux capacitors?

@moof @jmovs @osma I have neither the knowledge nor the tools to do either of those things!

@jon I recently got into electronics and started reading a multi-kg book on the topic. Greatly enjoy your monitor debugging saga, even though I don’t know enough yet to help 🤓

@jon not sure how comfortable you are with soldering, but you could remove the connector from the faulty board and mount it on the healthy one. The old connector on the healthy board can even stay in place.

Another option could be modifying the cable, and swap the connector on one end. From the pic (though not 100% clear), it looks like the connections match. Just a different type of slot.

@jncn Soldering: I can do basics, but this is far too precise for me to attempt.

The cables do indeed match, so I could I suppose re-purpose the plugs. That might be easier than soldering the mainboard.

@moof I am now told this is a joke 😄 but gauging by the responses from others, it was possible it was not! 🤣 @jmovs @osma

@jon @jmovs @osma Ah, I wasn’t sure if you’d picked up on that. I take it you’re not a trek or back to the future fan, then…

@moof @jmovs @osma I last saw back to the future a decade ago 😄

Here are the clues I was missing

The serial numbers have a letter on the end - S (for Samsung) and L (for LG) relating to the panel used in them

And there are revision numbers too

And yes, I ought to write a iFixit guide to all of this 🙂

@jon Got a cheap UPS you could try it on?

@parsingphase Sadly not. The only UPS I have is 12v for my router, not 240v

@jon @osma
Damaged electrolytic capacitors are likely*, but not always obvious. Checking capacitance with a simple multimeter is more reliable.
* especially true for devices with a long service time (the electrolyte is not stable over the long term)

@DerReparierer has helpful info:
https://derreparierer.codeberg.page/derreparierer/tutorials/capacitors/readme.html

The „Consumer Electronics“ section also covers monitor problems.
HTH.

@jon This feels like the old iPhone thing with the Samsung vs TSMC chips (I think)...

@jon Not sure if an option, but how do you feel about hanging monitor, computer and always-on peripherals like backup drive(s) off a UPS? That would effectively put them on a separate circuit.

@danyow I only have a UPS for my router at the moment, but that’s 12v not 230v. I’m not going to buy a 230v one just for this!

@jon makes sense! To be honest, I have no clue what second hand UPSes off eBay are being traded for these days. I just figured that getting a cheapish one would do the trick and might be less hassle than acquiring and then installing the appropriate board.

@danyow simpler solution: get a second hand 4K monitor to replace this one. Keep the Dell as backup. Sell the old Samsung for €20 online. It’d be cheaper than a UPS!

It’s fixed!

Three Dell U2715H monitors cannibalised into one

I’ll explain tomorrow how I did it. And there were two issues, not just one