How to remove this from notebook power supply?

Discussion in 'Technical Repair' started by UnnamedUser159, Mar 29, 2018.

  1. UnnamedUser159

    Thread Starter Member

    May 3, 2016
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    It`s about that white stuff.

    I have tried with mine screwdriver but obviously not so carefull because have removed a SMD element.

    Thanks in advance
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    That's silicon sealant, you could try a strong grease remover like Trichloroethylene.
     
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Why do you want to remove it? It almost certainly covers the high voltage (lethal) parts of the circuit.

    ak
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    There are companies that sell chemicals to remove/dissolve potting compounds..
    Depending on the amount of times you intend on doing this sort of work it may be cheaper to just scrap the power supply..
     
  5. UnnamedUser159

    Thread Starter Member

    May 3, 2016
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    There are companies that sell chemicals to remove/dissolve potting compounds..
    Depending on the amount of times you intend on doing this sort of work it may be cheaper to just scrap the power supply..

    Could you give me a link for that product from ebay/aliexpress ?
     
  6. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    Just out of curiosity I stripped down a dead LED bulb. It had that white stuff everywhere. It was completely encased in it. I used a small stick shaved to a chisel point and just scraped the stuff off. Had to re-sharpen the stick a few times but it worked for me. But I don't know if the stuff I encountered is the same stuff you have.

    In years of the electronics field I've had to remove some pretty stubborn stuff. I've always done it with tools, not chemicals. However, working with wood, I've used chemical strippers to remove paint and other finishes. Believe me, the chemical way is not as easy as just spread the stuff on and wait. You have to clean it up safely and dispose of the used chemicals properly. And some chemicals have to be neutralized before you can dispose of them.

    As to what @AnalogKid said, why do you need it off? What are you intending to do with the circuit? Perhaps there's a better way someone here can advise you on.
     
  7. jpanhalt

    Expert

    Jan 18, 2008
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    If it is silicone (or a 2-part RTV) the true "removers" work by denaturing the rubber. That is, effectively cold charring it. For silicone, the true removers with which I am familiar contain sulfonic acids (e.g., R-SO3H where R is a hydrocarbon chain, aka an alkyl group). They are hydrophobic, strong acids (like sulfuric acid) and penetrate the silicone to denature it. A closely related version is an ester of sulfuric acid, ROSO3H . Its action is by the same mechanism, but it is less stable in water. In either case, they are not kind to electronic components or epoxy.

    An alternative that is sold as a "green" silicone remover is not much more than an aliphatic alcohol that penetrates the rubber and aids scraping it off. In my experience, they do not work any better than a DIY version that consists of a mixture of 99% isopropyl alcohol (IPA, the less water the better) and light mineral spirits. The ratio is not critical. I use a 2:1 mixture of IPA to mineral spirits to help remove silicone caulking. It is still a mechanical process, however. In your situation, you might use a felt pad saturated with the removal aid on a rotary tool at very low speed. But, a small stick with a flattened end as mentioned by Tonyr will help.

    John
     
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  8. MisterBill2

    Distinguished Member

    Jan 23, 2018
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    I have removed some kinds of silicone encapsulation materials with a soak in gasoline. But do it outside in a jar with a lid that you can close. After a day's soak the stuff should either brush off nicely or be unaffected. If it comes off nicely then all that remains is to get rid of the gasoline smell. Extreme caution is needed because gasoline is highly combustible. That is why only doing it outside.
     
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  9. recklessrog

    Well-Known Member

    May 23, 2013
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    Paraffin (kerosene) works on some types and is less dangerous to use than gasoline. Leave to soak overnight.
     
  10. Tonyr1084

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    Sep 24, 2015
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    I've spilled brake fluid on rubberish stuff before. Some rubbers are not designed to handle the brake fluid and will soften and swell. If I had to guess, perhaps brake fluid might take it off, though I've never thought of trying that before. Then a good brake cleaner spray should remove the brake fluid. I just don't know what it might do to other parts of your circuit. It could destroy wire insulation and cause you more headaches than you want. But it's the thought that counts. And I'm counting.
     
  11. MisterBill2

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    Jan 23, 2018
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    Brake fluid is far more expensive than Gasoline, and once used for this it must not be used in a brake system. The gas that does not soak into the silicone material is still OK to use, and so it is much cheaper. And in some areas brake fluid may be a whole lot more expensive.. And given the world wide realm of participation we have, I try to stick with the possible and cheap.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Brake fluid may cost a little more than gas, but you don't need much and it's far safer. I can't comment on its effectiveness.
     
  13. Tonyr1084

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    Just thinking outside the Cheetos bag. Would need hardly any. Just enough to coat the affected area. But the bigger concern is the cleanup afterwords. And given how I've seen it eat paint, it'll probably eat whatever that white stuff is. I said "Probably". Probably is not a guarantee. Might need a teaspoon full. Maybe a tablespoon. Certainly not much wasted.
     
  14. ian field

    AAC Fanatic!

    Oct 27, 2012
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    Silicon sealant has negligible tensile strength.

    Solvent will take a while and could degrade winding insulation on the chopper transformer. some components don't have solvent fast markings, but rarer nowadays.
     
  15. MisterBill2

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    Jan 23, 2018
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    But you can't purchase a spoonfull of brake fluid. It comes in pints and quarts, and around here the stores only seem to carry the quart containers. Not everybody keeps a container of brake fluid in their car, since the stuff will absorb moisture. So purchasing a quart to use a spoon full is a very expensive way to go.
    Doing it with gas simply requires a bit of sense. Keeping the process safe is entirely possible. I have already described the safe way to do it, which none of these steps was hard or complicated. Irrational fear because somebody someplace did something dumb is not at all logical. People pump gasoline into automobile fuel tanks every day and nobody has any problems except for those who refuse to follow the very simple safety procedures.
     
  16. wayneh

    Expert

    Sep 9, 2010
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    The discussion is moot anyway. There are many different formulations that can be labeled “brake fluid” and we don’t know if any of them (or gasoline) work on the stuff.
     
  17. ian field

    AAC Fanatic!

    Oct 27, 2012
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    AFAIK: they've "universalised" DOT 4 and it doesn't make such good paint stripper as it used to. Dot 5 is silicon, but it has some nasty additive to make the seals swell a little - it might do some minimal damage.
     
  18. MisterBill2

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    Jan 23, 2018
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    Those are some of the reasons that I suggested a bit of gasoline, along with a large measure of caution. But not even a drop of fear.
     
  19. ebp

    Well-Known Member

    Feb 8, 2018
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    It is very easy to find charts of chemical resistance of silicone RTV.

    I have a whole range of solvents I use for a variety of things. I would not attempt to remove silicone from a PCB with a solvent, except perhaps for spot cleaning. Long exposure time would be required and there is too much risk of damage to components. You cannot keep the silicone adequately "wet" with solvent without exposing the components to vapors. I would use mechanical means only, including abrading with a natural or synthetic brush in a rotary tool. I'd probably try toluene, xylene, percholorethylene or chloroform for spot cleaning - none will dissolve it but all will degrade it.

    This is a chance that the silicone was "filled" with something, such as zinc oxide, to make it thermally conductive.
     
  20. MisterBill2

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    Jan 23, 2018
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    That is the other reason for using gasoline, which is that it does not harm most electronic components. And it did not dissolve the silicone, but rather made it swell up and tear itself off of the components.
     
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