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How to replace a DC jack?

Discussion in 'Hardware' started by dmmd01, Oct 31, 2011.

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  1. dmmd01

    dmmd01 Thread Starter

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    Hello,
    I've inherited a Gateway MC7321u with a bad DC jack. This was deduced by the sparks coming from the DC jack whenever it was plugged in. This is my first time attempting this type of work, but since it didn't cost me anything, I figure it is worth a shot and worth the learning experience.

    I have taken apart the computer, removed the bad (and burnt) DC jack, and removed the solder... The DC jack consisted of 5 numbered/labeled points on the board. Here is a picture of what it looks like brand new:

    [​IMG]

    Points 2,3,4, and 5 are the flat rectangular points, which I'm guessing are just for securing the DC jack to the board. Point #1 was the big round piece protruding through the board to the opposite side. This is from where the sparks were coming. Because there really wasn't much left of the previous point #1, I'm unclear as to how this connection should be made... Is it simply a matter of soldering it closed? Should the whole hole in the board be filled with solder?

    Any help would be appreciated. Thank you!
     
  2. raybro

    raybro

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    I'll attempt to help you, but not looking at the circuit board, I'll be making some guesses.

    First, some basics...
    Assume all of the metal contacts (points) serve an electrical function. If you can see the printed circuit to which they connect, you should first remove all the existing solder from the metal vias (holes) on both sides of the circuit board. This should be done very carefully using a a handy little thing called "Solder Wick". It's made of very fine solder coated copper braid material impregnated with solder flux. It does just what the name implies. Placing it on the solder joint and gently applying heat with a soldering iron, results in the solder being wicked towards the heat source. You should be able to purchase some at electronics outlets such as Radio Shack.

    Next, you need a low wattage soldering iron. Something on the order of 50 Watts. One of the most common errors made by amateurs when attempting this kind of project is applying excessive heat and/or mechanical pressure which in combination can lift the printed circuit trace/pad from the board surface.

    If the via pad is already damaged, a workaround would be to solder a piece of solid conductor copper wire between the trace leading to the pad and the contact on the component. Solid mechanical contact between the metal components is a must prior to soldering. A solder joint has little mechanical strength and is intended to simply hold the encapsulated contacts in place.

    When the circuit board connection points are clean of old solder, use electronic grade isopropyl alcohol to and a small bristle brush to clean them of any flux residue. You should be able to get those also at Radio Shack.

    The soldering process should be quick and straightforward. Have the component securely clamped to the board surface, place the soldering iron tip next to the contact protruding through the circuit board, touch the resin core solder to the tip to establish a thermal bridge, then apply a small amount of solder to the opposite side of the joint. The solder will flow towards the heat source. Actual time to form the completed solder joint should be on the order of less than a second.

    It may be helpful if you would take a photo of the area on the circuit board where the component is to be mounted. Both sides if possible.

    I found this web site wich will give you some info on desoldering.
     
  3. dustyjay

    dustyjay

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    Raybro has some good advise, however I would reduce the soldering iron wattage to no more than 30W, also from radio shack, purchase 63/37 (Eutectic)solder instead of the average 60/40 solder. 63/37 solder melts at a lower temperature, and has no plastic state (when the heat is removed it solidifies nearly immedately) reducing thepossiblilty of cold solder joints. Also if you can, get a soldering iron with interchangeable tips, and use a 1/8th inch chisel tip. As stated do not linger with the soldering iron at the joint as you risk damaging the circuit board substrate material and lifting the Traces and pads off the board. Be aware that some of the soldering points on the board may have multi layer connections on the board (circuit traces on both sides of the board and possibly traces in between layers as well.
     
  4. dmmd01

    dmmd01 Thread Starter

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    Raybro and Dustyjay, thank you both for your assistance. I've taken a few pictures of the board, both front and back. I see now that small flecks of the board material has flecked off, though I can't tell if it causes contact with any other point. Again, this was all free, so there is nothing lost if I try to fix it and it doesn't work. This has already been a wonderful learning experience. Here are links to the pictures:

    http://www.flickr.com/photos/[email protected]/6302483310/


    http://www.flickr.com/photos/[email protected]/6302482834/

    Thank you both!
     
  5. raybro

    raybro

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    Next step would be to get the area of the contacts on both sides of the board cleaned up. I would remove the charred residue using a mechanical method. In other words scrape it off as best you can. Do not use anything metallic. If you can find one, I suggest using an "Orange Wood Stick". They are used by manicurist to push the cuticle. It may help to use a hair dryer to warm up the surface. Be sure and not concentrate the hot air flow in one spot on the board, but rather pass it over the surface in a pattern. When the surface is warm to the touch, that's enough.

    When that is done, take photos of both sides of the board. Try to minimize any reflection of the flash from the surface by either shooting at an angle or not using a flash while backlighting with a lamp.

    What I'm interesting in is whether there was electrical connections on only one side of the board or both sides. What it looks like at this point is points 2, 3, 4 and 5 are connected to a common point (probably a ground plane) on the back side of the board. I just want to be clear about that. Cleaning it up may clarify that question.

    What is your observation in that regard?
     
  6. dmmd01

    dmmd01 Thread Starter

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    Well, I may have messed this up pretty well. I was attempting to clean up the points and managed to both refill and scratch the board. As you can see in the pictures, point #2 is filled. That is where I managed to lose my balance and scrape the soldering iron across what appears to be the ground plate. Points 2,3,4, and 5 all connect to the opposite side of the board and appear to go nowhere. The only one that seems to "go" anywhere is #1, which is where the burning was occurring. I cleaned it up the best that I could. A lot of copper seems to be exposed.
    Any thoughts?

    http://www.flickr.com/photos/[email protected]/6303724892/in/photostream
    http://www.flickr.com/photos/[email protected]/6303198977/in/photostream/
     
  7. dustyjay

    dustyjay

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    Solder points 2 thru 5 are definitely the ground plane. Use Solder wick as suggested by Raybro to remove the excess solder from them. Solder point #1 looks to be the problem you are going to have. There appears to be charring of the substrate. But this may not make the installation impossible. You need to clean solder point number one. I suggest a red pencil eraser as a cleaning tool. It is slightly abrasive but not dramtically so. DO NOT use a white, ink type eraser, as they are far roo arasive and will remover the copper of the circuit trace. Then you will be able to tell if Solder Point # 1 is still connected to the circuit trace as it should be.
     
  8. raybro

    raybro

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    Give us a detailed description of that exposed copper. Does it appear to be on the side of the board shown in the photo where its visible? Is it possible it is an internal layer. An internal layer would be within the 2 surface layers. Could it be the bottom side of the copper on the opposite surface?

    What needs to become clear is how the components near the charred area are connected to the exposed copper (if they are). The components to which I refer are labled R1 (Resistor) and what may be a capacitor or a diode next to it.

    Understanding what we are seeing is difficult with 2 dimensional photos, so you will have to be our eyes.

    BTW... I do not see any damage you have done so far which would have any real impact. Mostly cosmetic in nature.

    Follow through with dustyjay's advice and send some more photos. Get as close a shot of the damaged area as you can. Also try a different perspective so the board surface around the damaged area is fully visible and not hidden behind any other components.
     
  9. dustyjay

    dustyjay

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    A close up shot of the DC Jack that you removed might help as well.

    The only damage I see that has me concerned is around solder point #1. It actually appears as the solder point may no longer be attached electrically to the motherboard. This would actually be repairable, but to see what an undamaged motherboard of the same model looks like would help. I will be trying to find somewhere that might show this motherboard.
     
  10. dmmd01

    dmmd01 Thread Starter

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    I'll be out of commission tomorrow, but I will get more high resolution images on Thursday.

    Although I could be wrong, I believe that the copper that is exposed is an internal layer that is on the same side as camera. My reasoning for that is because while there is definitely some thickness to the copper it tapers off at the hole and there is a bit of charring inside the hole that would not come clean like the copper did... Thus making me think that it doesn't go all the way through.

    Again, I will get better pics on Thursday. Thank you both for your help!
     
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