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Soldering: a technical question

Discussion in 'Electronic Repair' started by moonlite, Sep 26, 2006.

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  1. moonlite

    moonlite Guest

    I'm working on a high end DVD player. It seems I am unable to make the
    solder joints on the board take solder no matter what I do. I even
    tried to add solder to the joints hoping that would help in the
    desoldering process but they simply won't take. Is it possible this
    board is manufactured differently to make servicing not possible
    without specialized tools only ASC's have them ?

    moonlite
     
  2. Arfa Daily

    Arfa Daily Guest

    If it is an up to date machine, then it will be manufactured using the
    dreadful new-fangled save-the-planet brigade's lead-free solder. In order to
    repair it with any hope of long term chemical stability of any reworked
    joints, you will need to be using using lead-free solder to rework them, and
    in order to do this, your iron will need to be around 30 deg C hotter than
    it needs to be for standard leaded solder. If you look carefully at the
    board with a strong magnifier, you will likely see that every joint has a
    dull grey dry ( american " cold " )look to it. Welcome to the world of
    lead-free ...

    Just as a matter of interest, what is the machine, what is the problem that
    you are trying to fix, and what soldering equipment are you trying to use
    for the job ?

    Arfa
     
  3. N Cook

    N Cook Guest

    Are things going to get that bad?
    I've not met this new health & safety junk yet, eg at the moment repairing a
    1974 Rotel amp
     
  4. moonlite

    moonlite Guest


    Thank you very much for this reply! I knew something was up because
    I've been soldering for a long time but never seen this. The unit is a
    Samsung, very fancy DVD player. Sometimes it freezes so I decided to
    give the main board a look. I did find what appeared to be, like you
    said, cold solder joints. I guess that's not "cold" after all. Is this
    lead free solder sold anywhere ?

    moonlite
     
  5. ian field

    ian field Guest

    Where are you? - Maplin sell it in the UK, its actually becoming hard to
    find lead/tin solder!
     
  6. N Cook

    N Cook Guest

    I niaively thought that if I should come across such a pcb with this
    lead-free stuff and a cold joint then all I'd have to do was remake the
    joint by adding traditional solder into the mix.
    But I take it now that they are incompatible, which presumably means that
    even solder sucking away all the original from component lead lead and pad
    would still leave contaminated surfaces that still would not take
    traditional solder for a more durable joint - opinions/knowledge anyone ?
     
  7. ian field

    ian field Guest

    Most of the monitors I used to repair had been assembled with lead free for
    a couple of decades - this was by far the most common cause of failure!!!

    As of yet I have never bought any lead free solder and the only problem I've
    had is if the lead free isn't sufficiently diluted with lead/tin, it remains
    "stringy" and causes solder bridges! Use plenty of flux but be mindful of
    the measures needed to clean it off after!!!
     
  8. Claude

    Claude Guest

    I wouldn't be surprised if they are using metallic glue (cold) for
    electrical connections.

    --

    50% of all statistics are wrong. The rest don't matter.


    Claude Hopper
     
  9. Arfa Daily

    Arfa Daily Guest

    Well, it's sold everywhere here now, and regular leaded solder is becoming
    more difficult to obtain, but I'm assuming that you are on the US side of
    the Atlantic ?? The Americans, as I understand it, have not been so keen to
    adopt this lead-free technology as the far east and Europe have. It's now
    law here under a directive called RoHS ( Restriction of Hazardous
    Substances ). The US military, for instance, flatly refuse to use it on
    reliability grounds. Over here, the avionics and medical instrument
    industries have been granted exemptions, and decisions on many others are
    pending. Never-the-less, the far east have been manufacturing in this
    technology for about 3 years or so now, so I would guess that most if not
    all of the US imports of these products from the far east locations, are
    built with lead-free. This being the case, I would expect that lead-free
    solder would be readily available. Indeed, Sony for instance, have insisted
    that their official dealers over here, use ONLY lead-free to repair ALL of
    their products, for the last 2 years, irrespective of whether they were
    originally built in leaded or lead-free. As you can imagine, this has gone
    down like a lead ( Ha ! ) balloon in service departments ... The solder
    industry itself seems unable to make up its mind as to whether mixing leaded
    and unleaded solder causes a long term problem. Half say you shouldn't, half
    say no problem. I recently wrote an article for a magazine on this very
    subject, and took some expert advice on this point, and his reckoning was
    don't mix if you don't want a long-term unstable joint.

    Anyway, on your Sammy problem. It is rare for a genuine electronic fault to
    be responsible for any kind of freezing. Commonly, it is caused by either a
    defective / worn laser, or a mechanical issue with the laser sled transport.
    As a first move, ensure that the laser moves silky smooth the whole way from
    one end of its slides to the other. I had a Sammy last week that had a
    tendency to freeze up about 30 - 40 minutes into a disc. The cause was
    distortion of the plastic runner that one side of the laser ran on. You
    could feel the laser get tight as you moved it towards the back of the deck.
    This was cured by slight rubbing down of the plastic with very fine carb
    paper, followed by metal polish. You can also get poor sled movement as a
    result of the pinion on the sled motor splitting. If you move the laser by
    hand, you get a bump-bump-bump as the pinion rotates past the split.

    Sad to say though that the majority of freezing problems are down to the
    laser itself. If the laser is iffy, it will have a lot more trouble reading
    home-burns than commercial pressings, and will tend to freeze on them more
    readily. Conversely, an audio CD will normally play faultlessly. Not an
    absolutely definative test for laser condition, but usually a good
    indicator.

    Arfa
     
  10. moonlite

    moonlite Guest

    Arfa, I can't thank you enough for this info and for taking the time to
    explain this lead-free issue. I am sure the readers of this post also
    appreciate your effort!
     
  11. moonlite

    moonlite Guest

    Arfa, I can't thank you enough for this info and for taking the time to
    explain this lead-free issue. I am sure the readers of this post also
    appreciate your effort!
     
  12. Andy Cuffe

    Andy Cuffe Guest

    I've never had any problems working with lead free boards. The solder
    is a little harder to remove, but it should take regular Sn/Pb solder
    fine. I don't know what the long term reliability will be, but
    everything looks fine and I haven't seen any problems yet.

    It sounds like your soldering iron just isn't powerful enough. Multi
    layer boards with lead free solder will require a much more powerful
    soldering iron than you can get away with on a single sided board. I
    highly recommend a 40W or greater temperature controlled soldering
    station for working on any modern electronics.

    Andy Cuffe

     
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