Oxides

Discussion in 'General Electronics Chat' started by R!f@@, Jun 11, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    As u all know I am every where getting things done.
    A petrol dispenser gave away yesterday and the geeks there brought me this.

    [​IMG]

    [​IMG]

    [​IMG]

    Now I have seen these kind of oxides forming.
    I just like to know whether there is chance that the chips will stay intact.
    I have dealt with this kind of things before but the outcome is not good.
    Do you think that after cleaning and replacing faulty ones, the board will give a good service life if I insulate it with varnish.
    As you can see from the IC pins, rust and oxides are every where.
    I think it will kill the semiconductors inside, what do you think ?
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Probably not going to cause internal damage, but it will make conductive paths all over. And be very hard to clean out from under DIP's.

    I saw something like this when the stainless tubing joint leaked all over an HPLC control board (clever routing there) and ruined a 68020 plus memory.

    If you can get it clean and functioning, try some kind of conformal coating to keep the crud off - http://www.electronics-project-design.com/ConformalCoating.html

    I'm surprised that coated boards aren't mandatory in your ocean environment.
     
  3. R!f@@

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    Who is there to check them...no body...
    government or another regulatory body don't have the technical know how..

    I am the one who understand these but am too little to be noticed.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I'd try stripping the corrosion away by putting the whole board in a container of muriatic acid for about a minute. Muriatic acid is diluted hydrochloric acid. In the States, you can buy it at pool supply stores.

    You don't want to breathe it's fumes, get it on your skin/clothing, or spill it on anything. Keep a couple of buckets of water handy just in case of an accident.

    After you've soaked it for about a minute, rinse it really, really, really well in fresh water. Then see if you still have "problem" areas left.

    It works great for cleaning off a variety of corrosion, but you have to make certain that you've neutralized it by dilution.

    After it's repaired, go for the conformal coat.
     
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    If you have access to a ultrasonic bath and DI (better) or distilled water you could clean most of the gunk away. Using a low setting and changing the water as soon is it gets dirty until it stays clear. Then bake the board at about 100F for several hours until it's dry, then (I'm not joking) place it in a zip-lock bag with uncooked white rice (desiccant) for a day. I would then spray it with something like deoxit to stop it from re-oxidizing.

    If you don't have a ultrasonic tank a stiff toothbrush (new :)) also works.
     
  6. R!f@@

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    Thanks guys.
    Sgt.
    Won't the acid bath strip away the paint and numberings and all that.
    what about the big caps?

    Spook
    Why the uncooked rice.
    won't the ultrasonic bath destroy electrolytic caps
     
  7. SgtWookie

    Expert

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    No.
    However, the ultrasonic bath will. :eek: So will lacquer thinner.
    Replacement of electrolytic caps that have been in service on a board that has failed should be just about automatic.

    Take them off, and replace them with fresh caps.

    I'm not Spook, but he is correct - I omitted that from my post. Prior to conformal coating the boards, they should be placed in a pre-heated warm (200°C) oven for at least 4 hours before putting on the conformal coat.

    I'd be more worried about the IC substrate interconnecting wires.
     
  8. nsaspook

    AAC Fanatic!

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    Like I said, it's a desiccant (rice in a salt shaker) and will adsorb any left over moisture. Ultrasonic cleaning works by cavitation, with a low power setting it's safe for a short periods of time because the electrolytic paste is fairly dry, almost all the energy will be dissipated on the surface in contact with water. I've cleaned some boards with years of cigarette smoke or soot from electrical fires with good results using DI. His boards are not really that bad so just brushing might do the trick.
     
  9. nsaspook

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    Any modern plastic IC has a coat of polyimide to seal the chip and bonding, this stuff is just about bullet proof.
    www.ultratech.com/pdf/fotopack.pdf
    http://www.google.com/url?sa=t&sour...v9mKDA&usg=AFQjCNE1tNhbzMcJ1mVzaWj3QmqwjvtAnQ


     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Is the "oxidation" just cosmetic? Physical cleaning with a toothbrush and water -- maybe with a little detergent added -- would be my first step. Alcohol (ethyl or isopropyl) with a little water (20%) also works. Phosphoric acid or polyphosphoric acid ("Naval Jelly") works well for removing rust. BUT, is the rust on the TO-220 devices from the device or from what they were attached to? I wasn't aware the tabs were made of steel. None of the ones in my part boxes are steel. So, if it came from something else, it will probably wash off easily. If you can get the cleaner used for jewelry and watches, that should also work.

    I would be reluctant to use concentrated HCl (pool muriatic acid is quite concentrated). It is almost impossible to get rid of all of it, particularly on plated items.

    As for drying, 200°C sounds a bit high. Perhaps, 200°F was meant. I second the desiccant idea.

    I suspect the oxidation is more cosmetic than anything else. I would look for obvious globs of gunk, remove them, gently clean, trouble shoot, fix, then final clean. Why spend a lot of effort cleaning and drying, if you can't make it work? Why risk damaging it from the cleaning, which will give you a two-fault situation and is much harder to troubleshoot?

    John
     
  11. R!f@@

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    The triacs are the ones giving trouble. Gate resistance are way off in some.
    Already removed the IC's to clean the underside...
    Caps are good. This is just dust and salt air pollution.
    A thinner bath cleaned it quite well I must say.
    Trying to get new triacs...
     
  12. PackratKing

    Well-Known Member

    Jul 13, 2008
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    You just nailed half or better of the problems facing the industrialized world...........Politicians who don't know their a** from a hole in the ground about what they are attempting to regulate :mad::mad:

    [[[ more truth than bad attitude here !! ]]]
     
    Last edited: Jun 23, 2010
  13. R!f@@

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    Ya, more like corrupt politicians.
    Those dumb m**********'s don't know any thing technical to regulate anything.
    top of that they not honest doing there job too.

    So what can they do when their lives are rusted
     
    Last edited: Jun 13, 2010
  14. retched

    AAC Fanatic!

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    Jeesh, tourist dollars corrupt as completely as tax dollars. But, this isn't a political forum. Unless you want to replace them with computers/robots, or unless you want to move, or run for office, such is life.

    At least your free...ish.
     
  15. R!f@@

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    so you tax dollar problem like we have tourist dollar problems
     
  16. retched

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    Basically. We get taxed on things the government doesn't understand just so they have more money for raises and things they want.

    I cant really say things the government doesn't understand..but things the politicians who write the bills dont understand.

    You know what they do understand? They do understand they can make a ton of money from taxing oil and oil companies, but they do not understand what is involved with getting the oil from the ground and turned into the products we buy.

    And they DO understand the increase in their budgets from said taxes.

    The oil companies and customers pay for funds to handle oil spills but dont have the technologies to handle the spills.

    So the companies who are to blame for the problems also HAVE to be the heros who stop the disasters.

    And there is a 75 million dollar CAP on the amount companies are responsible for in the event of an oil spill.

    But, just like other addictions, where there is money, there is supply.


    Anyway, how is the PCB cleaning going?
     
  17. R!f@@

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    I really cannot get my head around what you just said, but to add another, our government is going to finalize a bill concerning tax. Ones this starts we'll have another judgment day.

    Coming back to the board.
    Since you all know I am the guy running around the capital fixing the government petrol dispensers when their high paid techs failed, this particular pump issue was due to their maintenance and or carelessness.

    Couple of weeks ago I was fixing another pump ( which still is stalled due to me being angry towards FSM, the government fuel company in Maldives) when the guy in charge asked me to checked another pump at another location, so we went and they said they hear a load squeeling noise inside. without giving a second thought I replied the fan bearing has worn out.
    Guess what? they started arguing with me that there isn't a fan inside and there is no moving parts beside the pump motor which is located way below giving out a loud noise.

    They swear that there is no moving parts inside the pump and I swear that there is a fan inside and I know the fan is failing and the bearing are worn out. I repeatedly said that there is a fan inside and it is giving up and it is not a major issue for the time being.

    It was my brain against there's.
    And it took around two hours to get the pump open after contacting the authorities to check what was the cause.

    Guess what.....
    After opening..every body saw a big AC fan inside cooling the PSU sink.
    and it was about to give up.
    Yaaaaaaaaaaaaaaaaaay!! Another pointer for me :p

    So. I told them it's not a problem. Just find a fan and replace it, even there techs can do that. But do replace before it stops or you'll have a huge invoice from me later. :D ( I did say that, even though, I meant it as a joke)

    And weeks later the guy in charge started calling ( I do not answer them on one call, due to the reason above, rather ignored the call for a few days to see what they are up to), Another call came from a higher authority asking me to check the pump. I asked what happened and they said that the pump lights have gone out and it is very difficult since one pump is in service around that location, and they need me to do it urgently.

    Further investigation revealed that the pump failed and the fan stopped so they took the fan and they could not find another replacement....they tried to replace it with a pc fan though....and something happened and after a few juggling here "n" a few juggling there....a lot of work went around and the pump was worse than before.
    They have taken out a faulty board too..

    Huraaaaaaaaaay!!! for them, they have finally managed to do something for their money's worth.

    So I asked...why the heck are you calling me for, ( remember this guy is not just a guy, I think he was HOD or something.) go ahead and do it, aren't you the people who baldly says this and that, and Maldives does not have the potential or the technical know how to fix industrial equipments.
    Why is he even at his job for that matter when he does not know how to deal with his job, I mean he is the head and he should know how these things operate and should be able to fix them without getting outside help.
    Or at least he can guide his techs the right way to do it. But nooooo.
    He wants the job cause he is a relative of some one powerful and so he is the only one who should be at that position even though he doesn't know squat.
    This is the problem I am facing here....
    Anyways...after a lot of talk I agreed to fix it.

    Guess what.....the fan gave up. and the triacs blew.
    They did not replace it then. Fan stopped. Components overheated and the pump gave up.

    I said to bring the board to check it, you have seen the board...now see the fan...

    [​IMG]
     
  18. retched

    AAC Fanatic!

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    Is that a cooked coil?

    It also looks like a relativly low CFM fan. Whats the average temperature in the Maldives? (I could google it, but I have a man thats local ;) )
     
  19. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    [​IMG]

    see the picture. Those are the triac's in that board.
    I like to know how you guys do to check em. I mean I just replace and test. works every time :p.
    Now I have too many and what I have is too much.
    I checked them and I know some are faulty but I really cannot tell from the meter results.
    This is something that has always bothered me. Testing triac's for leaks or gate problems are something I haven't yet quite familiar with.
    The pic shows the resistance between the gate and MT1, together with the Vf with the meter in diode check.

    They are 8A ones. what I have are 16Amps. The data sheets are attached for ur convenience.

    Now the lot I have are BTA series. Check the pic below

    [​IMG]

    I measured them the same way too.

    So can any one tell me how to actually test a TRIAC.
     
  20. R!f@@

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    Apr 2, 2009
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    that is not my main concern..
    this was due to the fact that their techs are too good