Theory behind "sometime works, sometime doesn't"

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  • Askic
    Senior Member
    • Sep 2018
    • 187
    • BIH

    #1

    Theory behind "sometime works, sometime doesn't"

    Hello guys,

    Today I watched a YT video about Macbook repair, posted by Paul Daniels. I enjoy watching repair videos in general, but this particular draw my attention. If you see part: https://youtu.be/KwwI62NGBSc?list=PL...tbkvew1c&t=356 around 5:55, where he found a corrosion around crystal,
    he said it explained such behavior.

    I'd like to understand how corrosion around crystal can cause laptop to work sometime and some other time doesn't work.

    I've readsomething similar but about electrolytic caps. If they are too old and lose capacity or have ESR increased, this can also cause similar behavior.

    Can you please, how this is possible, what is the theory that explains it?

    I know that someone can be a very successful repair guy if without understanding the details oftheory behind it, but I'd surely like to understand why is that. The thing is that I had few problems lately that sometimes work and sometimes don't.

    Than you!
  • RJARRRPCGP
    Badcaps Legend
    • Jul 2004
    • 6304
    • USA

    #2
    Re: Theory behind "sometime works, sometime doesn't"

    I know that a bad solder joint can cause that type of symptom.
    Had that with an old Bearcat scanner. (the power input connector had a bad solder joint)
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    Comment

    • Askic
      Senior Member
      • Sep 2018
      • 187
      • BIH

      #3
      Re: Theory behind "sometime works, sometime doesn't"

      Originally posted by RJARRRPCGP
      I know that a bad solder joint can cause that type of symptom.
      Had that with an old Bearcat scanner. (the power input connector had a bad solder joint)
      Yes, that is perfectly understandable. With bad solder joint, as device gets heated or change working temperature, there are heat dilatations that can cause a break in connection. Perhaps the same applies to corroded parts, I don't know if the joint solders can corrode.

      Comment

      • stj
        Great Sage 齊天大聖
        • Dec 2009
        • 30977
        • Albion

        #4
        Re: Theory behind "sometime works, sometime doesn't"

        crystals are a special case - you always want the area around them perfectly clean.
        any capacitance between the pins or from the pins to anything else - even a long track with nothing on it will cause the frequency to change or even stop it oscillating.

        Comment

        • Agent24
          I see dead caps
          • Oct 2007
          • 4944
          • New Zealand

          #5
          Re: Theory behind "sometime works, sometime doesn't"

          Keep watching to 7:38... the track was broken at the test pad due to corrosion.
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

          Comment

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