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Soldering iron problems

Discussion in 'Electronic Repair' started by Antony Gelberg, Jun 13, 2007.

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  1. Hi,

    I know this should be simple but isn't. I need to resolder a DC power
    connector on a laptop, due to dry joints.

    I can't find my old, rarely used soldering iron, so I went to Maplin and
    bought their cheapo 30W soldering iron.
    http://www.maplin.co.uk/module.aspx?ModuleNo=32909&doy=13m6

    I would have thought that is good enough for PCB soldering, but I can barely
    get the old solder on the board to melt, let alone re-solder the joint. I
    can't work like this, I'm going to arse about for hours and still not get it
    done properly. Is the problem likely to be the fine point nib that it came
    with? I have always used flat-tip bits in the past. Or is the Maplin iron
    crap, and should I have bought the Antek 30W instead -
    http://www.maplin.co.uk/Module.aspx?ModuleNo=45545&&source=14&doy=13m6 ?

    All advice appreciated.

    I should mention that I also tried my 100W soldering gun, like this one:
    http://tinyurl.com/2z8ehn .

    No luck here, but then I have always hated this tool and never been able to
    use it effectively. It's rated for 12 seconds use in a minute (don't know
    what happens if you go above that), but takes about 9 seconds to even get hot
    enough to melt solder. Are these crap, or am I not using the thing properly?

    Antony
     
  2. It is lead free, but that doesn't matter when I'm trying to desolder the OEM
    joint. I think it's just not hot enough but I'm surprised - I thought 30W
    would be plenty.
     
  3. mc

    mc Guest

    Do some practicing with other things first. A few things:

    - As someone pointed out, you may have lead-free solder, which has a higher
    melting point. But you should use it for the repair, since the connector
    probably has the same stuff already on it.

    - There may be an invisible coating on the soldering iron tip, or it may not
    be properly tinned. The last couple of mm of the tip should have a coating
    of melted solder, applied by you.

    - Some coaxial connectors have a nickel (?) coating that is hard to solder.
    Using fine sandpaper on them really helps, as does a rotary wire brush.

    Your soldering iron looks fine (low-end, of course). Is the tip tightly
    attached? Try loosening and retightening the screw while it is hot (use
    care).
     
  4. Jamie

    Jamie Guest

    Make sure the tip is tight.
    Make sure you're using the correct solder?, 60 tin and 40 lead for
    repair work.
    Use some extra solder paste to clean the area..
    It's possible you have Lead Free Solder, that's hard to work with..
     
  5. I'm just trying to desolder the existing joints at the moment.
    It does.
    But would this stop me desoldering existing joints?
    It's back in the packaging. :) Don't think swapping it for a 50W iron is a
    better idea? How about a flat tip instead of fine point?
     
  6. BH

    BH Guest

    Mass is more important that wattage.

    BH
     
  7. Arfa Daily

    Arfa Daily Guest

    If the laptop was manufactured fairly recently, it will have been
    constructed with lead-free solder - dull grey looking joints, and the board
    may have "Pb Free" or "PbF" either etched or silk screened on it. If it is
    lead-free, then there is your first problem, as the melting point is higher
    than solder that you are used to. The second problem is that you are
    attempting to solder a fairly large component, that will leech heat out of
    an iron very quickly, which brings us to the next point that the iron used
    must have good thermal inertia to overcome this effect, and a pointy tip is
    far from ideal to achieve this. Also, 30 watts may be a bit on the low side,
    particularly if it is lead-free solder. On the other hand, I would have said
    that the job *could* be done with that iron, by a person used to soldering
    daily. Remember for a start that old solder - even leaded - is much more
    difficult to melt than new, and it is usual to feed some new solder into an
    old joint, before sucking or wicking the joint clean.

    As far as your Weller gun goes, this should easily be able to cope. I still
    have my original one of these with a black bakelite casing, from when they
    first came out over 40 years ago, and it still works as good as new. Yours
    should certainly not take 9 seconds to get hot. 3 seconds tops. The problem
    is that you are not slackening and re-tightning the bit-wire retainer nuts.
    These irons work by the bit being a short circuit across a single turn
    transformer secondary, the primary being a coil connected directly across
    the mains. The single turn produces a low voltage, but with huge amounts of
    amps flowing round it, via the copper bit-wire, which then gets very hot as
    a result. However, the surface of this (soft) copper wire oxidises from the
    heat, and the resistance of the contact points, under the retainer nuts,
    goes up. It only needs to go up by a few tens of milliohms, to significantly
    reduce the current flowing round the shorted turn, and hence the amount of
    heat being generated in the bit.

    Click the iron's trigger on, and whilst holding it on, take your bit
    retainer nut spanner, and back each nut off a half turn, and re-tighten, one
    at a time. That should then give you virtually 'instant' heat each time you
    trigger it on, for the rest of the soldering session. You should repeat this
    procedure whenever you get the iron out to use. As far as exceeding the duty
    cycle of the gun, I have done this many many times. The effect is that the
    case becomes uncomfortably hot to hold, as a result of the transformer
    primary winding overheating. I suppose that if you managed to hold onto it
    for long enough, the insulation on the wire making the winding would fail,
    but I think that you would be seriously burning your hand by the time this
    happened, and already, your nose would be telling you to stop ...

    Arfa
     
  8. Jamie

    Jamie Guest

    My desoldering tool can do up to 60 watts/. I would get something in
    the line of 45 watts or so for desoldering Lead Free or, mix in some
    Leaded solder to soften it.
     
  9. Mass of the tip, correct?
     
  10. W Gray

    W Gray Guest

    Greetings.

    I hope this message finds you well.

    This may sound like a dumb question, but have you tinned the tip of your
    soldering iron?

    -W Gray
     
  11. Steve Sousa

    Steve Sousa Guest

    Hello:

    The why's of your problem have been explained by other posters.
    You can solder your dc jack with your 30 watt or the pistol, better yet,
    get a friend and use both, however, there is a trick to it: you have to
    preheat the pcb.

    To do so, get a hair drier, set it on max and slowly start heating a
    large area of the board from a distance of 20cms (8inch), then start
    aproaching and concentrating on the jack, it takes about 5 minutes to do
    it properly, your board will be very warm overall, then heat the board
    directly above and bellow the jack with the hairdrier nearly touching
    them, do this for about 3 seconds each side, repeat about 4 or 5 times,
    then and only then use the solder iron to remove the jack, if you have a
    friend you can use both irons, the pistol on the ground connection the
    other on the other pins. the jack should fall off. be very gentle with
    the pistol if you use it, because the board is allready hot, such beast
    will easily damage it if you aproach it like you did when it was cold.

    P.S: to use the pistol *first* heat it enough to melt solder *then*
    touch the parts then turn on-off-on-off at about 1Hz.

    Best regards

    Steve Sousa
     
  12. Jerry G.

    Jerry G. Guest

    The soldering iron has to have the right temperature, and have enough
    BTU's to heat the connection. Make sure you are using 60-40 type
    solder.

    A proper soldering station is what is normaly used. This will allow
    for proper temperature control, and can put out enough BTU's of heat.

    If you do not have a lot of experience at soldering on to circuit
    boards, it is very easy to damage the solder pads and traces on the
    board. This is especialy true with multi-layer boards. This type of
    damage takes a lot of experience to fix, it is not easily repairable.
    Not having the proper tools and experience can usually lead to
    damaging the circuit board, and sometimes the components that are
    being heated.


    Jerry G.
    ======
     
  13. Smitty Two

    Smitty Two Guest

    You need flux. I'm surprised my friend Arfa didn't mention that in his
    otherwise thorough treatise.
     
  14. mc

    mc Guest

    I'm just trying to desolder the existing joints at the moment.

    Ah. They may have a clear plastic coating.
    30W is plenty for electronics; 15W would do.
     
  15. Arfa Daily

    Arfa Daily Guest

    Hi Smitty

    I was taking that as a 'given' by assuming that the OP was using
    conventional flux-cored solder for his attempts, so flux would be
    automatically put into the equation when new solder was added to the old to
    help the melting process. However, if he's not, you're dead right, and I
    should probably have made that clearer as being part of the reason for
    adding new solder to the old joint ;-)

    Arfa
     
  16. Morse

    Morse Guest

    Antony,

    If you can borrow a temperature controlled iron, preferably one in the
    45-50watt region, with a fairly broad tip, you should be able to do the job
    fairly easily.

    What is happening is the large area of the multilayer PCB, combined with the
    rather large track area, is siphoning away the heat from the tip and
    chilling it. The iron is not temperature controlled so cannot compensate,
    so its temperature drops below the required heat to melt solder.

    If you keep trying with your iron, you will soon destroy the socket, board
    and PCB pads- the job must be done quickly with a hot iron. I have replaced
    several laptop power connectors and feel that a cheap hobbyist's iron in
    the majority of cases would be quite inadequate.


    Try eBay- I've seen old Weller magnastat soldering stations for about 15
    UKP. Usually tatty to look at but they do a great job. I still use one
    myself! The temperature is set by tip selection, and there's not much they
    can't do with a hot tip fitted. Alternatively there's occasionally Antex
    stations with user-variable temperature dials which go for a reasonable
    amount. If you intend on servicing your own stuff you really need a
    temperature controlled iron.
    Soldering guns are OK for the appropriate job but not really for PCB use
    because they can only administer very high heat for short bursts and need
    cooling off time before they can be operated again.

    To answer your question- exceeding the time will burn out the transformer
    inside! The one I once used went off with quite a loud pop!

    Morse
     
  17. mc

    mc Guest

    If you can borrow a temperature controlled iron, preferably one in the
    I agree. When I said earlier that 30 watts is plenty, I hadn't quite
    realized he was wanting to remove something with a substantial amount of
    metal that needs heating up.
     
  18. I've had success doing what you want to by using the largest iorn I can find
    and working really fast so that you don't destroy the board. I'd immagine a
    45 - 50 Watt iorn would work well. Just don't leave the iorn on the board
    more than a few seconds, just long enough to liquify the solder and add some
    more. You will cook those solder pads if you use too small of an iorn or
    take too long with a big one!

    Mike
     
  19. Smitty Two

    Smitty Two Guest

    I agree. When I said earlier that 30 watts is plenty, I hadn't quite
    realized he was wanting to remove something with a substantial amount of
    metal that needs heating up.[/QUOTE]

    OP: Again - Before you invest $100 or more in a quality iron - which I
    highly recommend - beg, borrow, buy or steal a couple of ounces of
    liquid flux. A drop or two will make a world of difference in your
    ability to reflow the old solder. Trust me on this one. You might just
    be able to get by with the light duty iron if you use flux, and you'll
    need it anyway even if you buy the better iron. And don't use the point
    of the tip. Choke up on it a bit, where there's more thermal mass.
     
  20. GregS

    GregS Guest

    After working with the Weller rework station, all the other irons seem
    way to large for the hand. The Weller being smaller in size is not small
    on watts. 80 watts. Pleasure to work with.When I need big watts, i get
    out the 250 watt Radio Shack gun.


    greg
     
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