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I have 3 u2311h monitors in an eyefinity setup. For aesthetic purposes, I do not want to replace the faulty one with a newer u2312hm. The problem with the faulty one is as follows:

For the past few weeks, when I turn it on, it flashes the screen (ps3, windows 7, whatever is connected) for a few seconds then turns black. Turning it off and on a few times and if im lucky, it sticks and works properly. Recently however, it never stayed on and always went black. I have read online that its a sign of faulty capacitors.

I have opened the monitor and there are two pcbs. One for the main power connector and one for the vga, dvi, usb etc. I cant for the life of my identify any capacitors that look faulty based on "spot a faulty cap" guides on the internet. None of them look bloated :/

I am fairly proficient with a soldering iron so I am confident I can replace any parts of the board. Am I going along the right tracks here or is this problem nothing to do with the capacitors? Also if it is to do with the caps, which ones do I replace? Ones on the power board, or the other board? or both?

Thanks

Edit: I have replaced all the small caps but unfortunately the same problem was still there. I didnt replace the massive cap on the board as an oversight. I have just ordered a new replacement powerboard anyway so that should do the trick.

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These sorts of symptoms (called "two seconds to black") generally indicate CFL issues – either in the lamps themselves or in the inverter. –  ntoskrnl Mar 16 at 17:39
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Whatever you end up doing Ozzy, don't forget to come back to let us know :D –  cde Mar 17 at 3:25
    
Don't forget that capacitors in modern switched-mode power supplies can be terrifying. Always make sure the voltage across the leads is safe. Discharging can be misleading too. –  ldrumm Mar 17 at 4:02
    
@cde, i will keep you lot updated :) –  Ozzy Mar 17 at 9:31
    
@ntoskrnl, ill have a look at that if the cap repair doesnt work –  Ozzy Mar 17 at 9:32

3 Answers 3

up vote 7 down vote accepted

It has been my experience that the problem symptom you have seen is related to bad capacitors in the power supply board. I've replaced such capacitors in almost a dozen different monitors that had the same symptom and ended up working like new after repair. There have also been a couple of monitors where capacitor replacement did not fix the faulty behavior of the unit.

Some hints to think about before you dig into things and rip everything apart.

  • Label all wire and cable connections before taking anything apart so you can easily get it back together again in the correct manner. There is usually a lag between opening the unit and when you are ready to snap it all back together again that could be even 10 to 12 days. It is easy to forget how it all connected.

  • Make up a detailed list of every capacitor on the board as you work including the location where each was soldered in.

  • Most monitor power supply boards are cheap cheap one sided boards. It is very easy to damage the board copper pads and lands when removing the old capacitors. Make sure to use careful techniques when unsoldering including use of solder wick. Make sure the leads are free before trying to pull out the capacitor or you risk ripping the pads right off the board.

  • Some capacitors may be mounted on their side and glued down to the board with a hard white compound. Best first trick with those is to slit open the outer plastic wrap on the capacitor with a razor knife so that the capacitor body can move around while you free the leads.

  • Measure all the capacitors accurately. Replacements come in many
    sizes and often size a replacement that is slightly larger may not
    fit correctly once the monitor chassis enclosure is put back
    together. Measure the length of the body, its diameter and the lead spacing. Replacements are often specified in metric mm dimensions.

  • When looking for replacements make sure to observe the temperature rating and voltage ratings. For instance do not replace caps that were 105C rated with 85C caps. The life time of repair will be significantly reduced if you try to scrimp on the replacements.

  • Select replacements from respectable vendors such as Panasonic and Nichicon. Stay away from unrecognizable brands like the types you are removing.

  • Note that the capacitors in these switching power supplies generally need to be high quality types with very low ESR and good Ripple Current ratings. Replacing them with cheaper garden variety capacitors is inviting early failure after the repair; if they work at all.

  • When reinstalling the capacitors make sure to observe the polarity markings and get the minus and plus sides aligned correctly.

  • I have found www.mouser.com to be a good source for replacement capacitors.

Good luck with your repair.

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Thank you for your detailed reply. I took a video of the disconnect process, luckily there are only a few cables that needed to be removed so it wont be difficult to put back. I will only remove the caps once they are ready to be removed. I have found some replacement boards for about £40 but just bought replacement caps from ebay for every capacitor i could find on the power board. better safe then sorry :) –  Ozzy Mar 16 at 17:10
    
The caps i went for were Panasonic Electrolytic Radial Capacitors and they are rated at 105c. hopefully these are good enough to do the job. I was unaware that capacitor polarity mattered so thank you for making me aware of that. Hopefully i will be able to resurrect this monitor :D –  Ozzy Mar 16 at 17:12
    
I have found it much easier to measure things by removing them ahead of time. Many times it can be near impossible to read the labels on the capacitors when they are still on the board. –  Michael Karas Mar 16 at 17:12
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Sounds like you are somewhat new to electronics things. Yes polarity is VERY important. So are capacitance and voltage ratings. Make sure that you purchase low ESR types. Some switchers will just not work with the more garden variety capacitors. BTW Panasonic has a broad range including both low ESR types and the garden variety types. –  Michael Karas Mar 16 at 17:16
    
@ozzy keep in mind, caps are easily and often counterfieted. Ebay panasonics might not be panasonics, nor the right size or capatitenc or any spec they say they are. –  cde Mar 16 at 17:22

Last bad (valuable) LCD monitor I had- one of the 30" Samsung monitors on my CAD workstation- was a BGA solder joint that went bad. Irritating when they don't match cosmetically and in terms of control placement.

Yours does sound like it could be the power supply. Maybe look at the startup resistor as well. I think these repair questions are considered by the powers that be to be off-topic, but perhaps it's interesting as an indication of where designs are vulnerable.

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BGA and samsung go hand in hand. With dell, its bad caps, 10 to 1. –  cde Mar 16 at 16:45
    
Im glad it most probably is the caps. I would hate to try and identify poor solder joints as every time I repair one, I would identify it again :P –  Ozzy Mar 16 at 17:14
    
@ozzy worse, bga is ball grid array, all the solder joints are under the chip. You need an xray machine to properly identify poor joints! –  cde Mar 16 at 17:31
    
.. lucky its a dell monitor then! ill just replace the caps, if that doesnt work, new powerboard for me –  Ozzy Mar 16 at 17:35

This does sound like a bad caps on the inverter section of the power board. Dell has used subtandard caps for the last decade. Prone to capacitor plague. But 90% of the time the caps are physically blown or leaking. Even without the physical signs, that it turns on for a few seconds screams bad caps. You can buy a new power board (or swap one from the other 2 working ones, for testing), or you can bite the bullet and replace all the large caps with some decent low esr, higher voltage, same capatitence parts. Typically only 6 to 10 caps needed.

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Is there a reason for higher voltage caps? I just bought replacement panasonic caps at the exact ratings of the ones on the board. Hopefully they will do the job. –  Ozzy Mar 16 at 17:13
    
@ozzy because the caps are undersized. If the voltage on the line spikes to say 20v, a 16v cap wouldn't be happy. A 24v cap wouldn't care. Dell went cheaper to save a penny or two per board, at the expense of product life time. Its not mandatory, but the voltage rating is a max tolerance spec. Next time go slightly higher voltage as a precaution. The same rated ones will do. –  cde Mar 16 at 17:19
    
ahh that makes sense. unfortunately, i am quite impatient when it comes to trying to fix things so bought the ebay caps before I read your answer. I will bear that in mind if the other ones die tho. Can it be a much higher voltage rating? or does it not matter as long as its reasonably bigger? –  Ozzy Mar 16 at 17:37
    
@ozzy the voltage rating is a 'max' spec. So it just needs to b higher than the voltage you will see on the line. The trade off is size. The higher the voltage rating, the physically bigger they tend to be. It could be a 1000v cap if that's all you have, but it probably won't fit. So just size it the next voltage up (16 -> 20 -> 24, etc). –  cde Mar 16 at 17:47
    
The caps specced at a higher voltage and the same capacitance tend to be either larger or higher ESR so I wouldn't recommend it. –  Gunnish Mar 16 at 22:05

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