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I'm not an engineer, but my monitor stopped working yesterday (it just wouldn't display anything but still gets power) so I figured I'd like to take it apart and see what went wrong. At the very least I'd get to see what the inside of a monitor looks like :). Anyway, I took it apart, and also read around about my issue and it seems the capacitors have gone bad, at least some of them. However, I also noticed some white elastic stuff all over the board. Some of them are sticking two capacitors together and to the board, but I also see some from where power socket connects to the board.

My question is, what is the white stuff? Should I replace all capacitors that have white stuff around it, and should I also replace the power socket part? Or should I just replace the bulging capacitors and leave it at that?

UPDATE: white stuff

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It's very likely to be fastening material for bigger components. Does it look very close to whats on the big capacitor in the middle of this photo, and also at the bottom of this picture, on the blue components. Edit: yes that very clearly looks like fixating material to me. They may have used it as a strain relief in this case for the mains wiring.

This is used to prevent any vibrations getting bad for the solder joints. The big component has a relative large weight and must therefore be fixated down more properly.

If you want to try and fix the monitor you could look for:

  • Dodgy capacitors, their tops are bulged. Replace with equal or higher voltage and preferably same capacitance (amount of uF's). Try to keep it as 'original' as possible, a capacitor that has a much higher voltage is larger, and less likely to fit (also consider the height, monitors are space constrained).
  • Burnt components.. well you should smell and see them. Usually black, toasted and not good. If so you may need to google around a bit to see if there is any information on what the component was (like forums, schematics..)

  • Dodgy transistors or soldering joints. I've fixed a monitor 2 years ago that had dodgy solder joints on the transformers (I just reheated them and added some new solder, didn't even had to remove anything at all) and 4 broken transistors. I was able to get 4 replacement transistors for 5-10$ and it worked for another 1.5 years.. it finally died, this time probably the video controller board (couldn't be bothered now, it's an old 17" slow monitor)

Usually I look for forums and other 'fix guides' on the internet to see what they are attempting and see if there is anything I haven't done yet. Usually one or a combination of these three faults are the most likely ones.

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  • \$\begingroup\$ The white stuff is intentional silicone or polyurethane insulating adhesive to prevent microphonics or fatigue on solder joints under vibration. The bulging caps are due to under-rated temp and high ESR from low cost alum. electrolytic caps. Change with 125'C caps with low ESR vs 85'C caps. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 17 '12 at 3:52
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The "white stuff" is a fast setting adhesive used to provide mechanical location for heavier components. Leave it alone as much as possible. I've provided additional details and some suggested alternatives below - although odds are you will not be replacing it.

Replacing the bulging capacitors MAY provide a fix but they may have been damaged by some other failure. Voltage rating of the new caps should be the same or somewhat more than the existing ones.
Capacitance of the new caps should ideally be as before, but larger is unlikely to cause a problem.


What IS this white stuff anyway ????:

That's sometime affectionately known as "Gorilla Snot" (hereafter "GS"). It's a relatively fast setting adhesive that is INTENDED to provide mechanical strength and/or rigidity to parts that should have been given it by proper means such as brackets or support rings, BUT they decide that they can get away with doing it on the cheap with this material.
They can and they can't. It tends to fail long term in many cases when stressed. If it doesn't fail it probably wasn't needed.

Sometimes used instead and no less effective is "hot melt" glue, applied at moderate temperature and sets as it cools. Like GS it too almost always fails in the medium to long term. Usually in months, sometimes weeks. It seems that the glue (aka melted plastic) hardens with time and loses any keying it has to most surfaces. It can be used with some utility by allowing it to pass through a hole or slot and to accumulate a "knob" or bulge on the other side, so that WHEN it releases the knob is too large to pass through the hole or slot. Such an arrangement could provide reasonable retention although maintaining tight positional tolerances may be difficult.

In my experience, a superior solution is to use a neutral cure silicone rubber. Extensive advice is available from manufacturers on what grades to use with various materials and conditions. Primers are available for some harder to bond materials. In most cases I have found that silicone rubbers provide superb long term seals and bonds. 20+ year sealing and retention in outdoor plumbing type use is common.

An exception I found was in attempting to bond a FR4 PCB backed PV panel into an ABS well in a portable light housing. Over time the ABS/silicone-rubber join would debond, just as GS and hot-melt glue do. In that case it was possible to key the rubber into holes in the housing so that retention knobs were formed, as mentioned above.

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  • \$\begingroup\$ ah ok, so its not something that leaked out of the capacitors? \$\endgroup\$ – GiH Apr 12 '12 at 20:23
  • \$\begingroup\$ @GiH - probably not. Photos always useful BUT a commonly used adhesive looks much as you describe. \$\endgroup\$ – Russell McMahon Apr 12 '12 at 20:24
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    \$\begingroup\$ @GiH The results of capacitor leakage are brownish, so most likely not. If you want get a 100% correct response, post pictures. Also try running it with alcohol on a cotton swab. If it dissolves easily (and most likely it won't), then it could be from capacitors. \$\endgroup\$ – AndrejaKo Apr 12 '12 at 20:24
  • \$\begingroup\$ thanks, i've included a pic, you can see the white stuff all over, mostly around blue things haha, blue wire and capacitors :P \$\endgroup\$ – GiH Apr 12 '12 at 20:33
  • \$\begingroup\$ ditto on replacing the bulging caps, a very frequent failure of LCD monitors. \$\endgroup\$ – kenny Apr 12 '12 at 20:45
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Notice that the white stuff is around parts that may move - non snap-in capacitors, wires, resistors in the air ... it's definitely fast-setting non-conductive adhesive.

As always, when replacing electrolytic capacitors, you must not only match the voltage rating and capacitance, but the ripple rating too - don't put general-purpose capacitors (only specified for 120Hz operation) in high-frequency power converter circuits that may see tens or hundreds of kilohertz, else they'll run hot and dry out quickly. The manufacturer usually specifies the high-ripple parts at up to 100kHz in the data sheet (and often referrs to them as 'high ripple' or 'low impedance').

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  • \$\begingroup\$ hmm... well how do i know what type to get, if its low-impedence, general purpose or high ripple as you say? \$\endgroup\$ – GiH Apr 12 '12 at 21:21
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    \$\begingroup\$ You have to look up what you're replacing! If you're replacing a Nichicon HZ for example, the datasheet says "ultra low impedance" and has ripple current specified at 100kHz. You cannot replace this cap with a general-purpose capacitor - you'll have to replace it with one with comparable ripple rating. \$\endgroup\$ – Adam Lawrence Apr 12 '12 at 22:05

protected by Community Dec 21 '13 at 5:29

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