help with a soldering problem

Discussion in 'General Electronics Chat' started by jaifra78, May 10, 2013.

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  1. jaifra78

    Thread Starter New Member

    May 10, 2013
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    hi i am a newbie and i have been tinkering with a soldering iron lately i have no training anyway my problem is that i was desoldering the wires off of a tablet mainboard to replace the battery and in the spot where the positive wire was this little piece of metal that i assume connected to the board came off from the board and now i cant solder the wire back in its place because that little piece just crumbled when i attempted to put it back but even if it didn't crumble i don't know how i would have gotten it to stick in place anyway so now there is only an empty square on the mainboard where the positive wire is supposed to go so my question is how or can i fix this any help would be greatly appreciated i can add pics if needed just let me know thanks
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Possibly a solder terminal, can you post some pictures?
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    my guess before the pics ..lifted solder pad..
     
  4. JohnInTX

    Moderator

    Jun 26, 2012
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    Yep. From the lifted pad, trace the circuit back to something you can solder to (terminal, another component, via on the PCB etc) and use an ohmmeter to confirm the connection between the two points. Then use 30ga wire wrap wire to fix it.

    The mobo will be multi-layer with internal signal runs so you may be out of luck.

    Consider a smaller iron to make the fix and practice on some scrap until you can get a good joint without overheating the board.

    Good luck.
     
  5. jaifra78

    Thread Starter New Member

    May 10, 2013
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    here are some pics i hope they are clear enough. its the spot where the positive led goes thanks for the help


    [​IMG][​IMG][​IMG][​IMG]
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    yep pads gone.. You will need to look at the board and find the trace it connected to and solder to that somewhere like JohninTx said.. Or call it trash and move on.
     
  7. jaifra78

    Thread Starter New Member

    May 10, 2013
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    how do i do that please be as simple in explanation as possible i am new at this:)
     
  8. #12

    Expert

    Nov 30, 2010
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    First, get rid of that overpowered soldering iron. Get a 10X jewelers loupe and a bright light to shine through the board from behind. That should lead you to a place where you can connect.

    When you get done with that, practice on a dead circuit board with about a 40 watt soldering iron, solder wick, add-on flux (water based or rosin based), maybe a suction type solder remover, and extra solder. I think you can be fairly well skilled in a couple of hours, but a military shop told me it would take me 3 days (36 working hours) to do their soldering course. I completed it in 35 minutes. There is a goal for you. Try to get good at soldering in somewhere between 1/2 hour and 36 hours.

    Lucky me. Simultaneous typing and I answered what you were going to ask!
     
  9. jaifra78

    Thread Starter New Member

    May 10, 2013
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    i dont know what i am looking for can you show me with a pic or diagram


    my iron is a 40 watt weller i do have wick and a sucker i need to get some flux the solder i use has a rosin core but i guess i need a tub of flux also. maybe my iron is getting to hot it says it gets up to 900 degrees:eek:

    i am working on a cheap Chinese tablet mainboard its really my first time doing anything like this before this i was fixing computers:)
     
  10. #12

    Expert

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    You already posted a picture. I think you know what a jewelers loupe is (It's a tiny magnifying glass.) and I think you know what a bright light is, so you must be asking about the connection points.

    Those slightly raised lines under the blue coating are copper "traces". They are the equivalent of wires. Look at the one that connected to the destroyed solder pad and trace it back to another component or a solder pad or someplace you can scrape off the protective coating and solder a wire to it. Then, solder a wire to it and run the wire to the place where the solder pad was lifted (destroyed) and connect that wire to the LED that you want installed at that place.

    This is about connecting an LED where the mounting point was destroyed, right?
    You are trying to make a connection from someplace on the path that brought power to the LED. You need to run a wire from someplace on that power line to the place where the LED is mounted.

    It might be a ground connection instead of a power connection, but that doesn't matter. What matters is that you establish a connection from someplace on that line and wire it to the LED.

    It might also be that your soldering iron is the right wattage and you merely pressed too hard and wiggled the soldering iron, thus sheering off the solder pad.

    Rosin flux is the right thing to use with rosin core solder but water based flux will work too. The problem with water based flux is that it has to be wet when you start soldering. I have tried painting a whole board with water based flux, letting it dry, and then soldering. It doesn't work. Touching a soldering iron to wet flux removes some of the heat and makes the process a bit less predictable. That is the main reason to use rosin flux. It doesn't wreck the temperature as much.

    Solder wick also becomes, "old". You can scrape it with your pocket knife to renew the surface, but that scrapes most of the flux off. That is why you need additional flux.
     
  11. jaifra78

    Thread Starter New Member

    May 10, 2013
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    @#12 yea i was talking about the connection point sorry if that was unclear i do know what the other stuff is:). yea the led that the pad came off of is the back light for the screen of the tablet so if i were to solder that to another area would it work like if you look at the pics there is a spot that says motor it has positive and negative solder points nothing was solder there when i took the tablet apart i assume its for a fan of some sort that was not added but i don't know do you think that would work or does it have to be soldered to the exact spot it came from
     
  12. #12

    Expert

    Nov 30, 2010
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    one of the solder pads for the LED is still there that will hold the LED in place on one end you can glue the other end down after you solder a wire to the LED i can't guess if the LED will light up the right stuff if you move it i can't imagine you re-routing the wiring for the LED to the motor connections if you can't figure out how to attach the LED where it belongs i also can't figure out why you can't use capital letters or punctuation
     
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  13. GopherT

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    Nov 23, 2012
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    Wait, before you go ahead, there are two types of 40 watt Wellers. One has a thermostat and keeps temps in the 600 to 700 degree range (depending on tips used). The other just blasts heat to the tip and anything it touches - best used for stained glass or non-PCB soldering. Your 900 degree model (without thermostat) may be causing more problems that benefits. You may want get a 20 to 25 watt model pr a thermostat model. If that is not possible, certainly do not keep power on your PCB for more than a second after the solder melts. Temps of 900C hot can burn the glue that holds the copper foil to the board.
     
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  14. jaifra78

    Thread Starter New Member

    May 10, 2013
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    there is no reason to be rude i didn't know i had to have perfect punctuation to ask for help on these forum geez chill out
     
  15. jaifra78

    Thread Starter New Member

    May 10, 2013
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    i think that its the one without the thermostat thanks for the help :)
     
  16. DerStrom8

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    Feb 20, 2011
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    40 watt is much too high for most electronics soldering. I only use my 40W iron for solder tabs and large connections. In most cases, though, I use my 15w. You could probably go up to 25W, but any higher and you risk pulling up the pads/traces on most boards.

    Matt
     
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  17. #12

    Expert

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    sorry i didnt know mentioning the obvious was rude ill try to control myself
     
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  18. GopherT

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    Nov 23, 2012
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    I agree that 15 watts is plenty. When I said 25 watts above, I couldn't think of the standard size for non-thermostated soldering pencils. Thanks DerStrom
     
  19. jaifra78

    Thread Starter New Member

    May 10, 2013
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    before you point out something "obvious" maybe you should think to yourself hey maybe this person has a learning disability and maybe i shouldn't say anything about it and embarrass them and make them feel bad about themselves when they are just trying to ask for help
     
  20. DerStrom8

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    Feb 20, 2011
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    You must realize, though, that when you type without capitalization or punctuation it makes it very difficult to read. We have to figure out where all the commas and periods are supposed to be, and split up the phrases into something that is logical. It wastes a lot of time, and can often lead to misunderstandings. It would be very helpful if you could try to remember capitalization and punctuation in your posts. It would make things simpler for everyone.

    Thanks.

    Matt
     
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