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Sell me your broken computer

identifying problem area on Macbook logic board?

edited April 2012 in General
hi all, i am trying to repair a late-2007 3,1 macbook 2.2GHz which had suffered a liquid spill and would greatly appreciate some help. i have some previous hit-and-miss experience of such repairs, usually by bathing the logic boards in 99% isopropyl alcohol and brushing them i have revived some, but others remain dead.
however, this particular one has made me think i could have more strategy to approaching the repair...

when i received this board, it wouldn't boot at all, and the magsafe charger light did not switch on. after one clean, it seemed to work great, so i re-assembled the machine with ram in both slots and used the computer for a couple of hours. after a couple of days i went to switch the machine on again but this time it would not boot. the harddrive spins up and the front white led illuminates, the cpu heatsink fan spins up, however it does not chime and the lcd does not display anything or even briefly flash like i have seen some do.

i thought perhaps it was a ram issue, so i have tested it with different ram, and with just either one of the ram slots occupied, but this has not made any difference. i also tested it without any ram in at all, expecting to get the front white led flashing and the "beeping" sound, but the behaviour remained the same as with ram installed, so i guess the problem actually lies somewhere prior to the ram being checked.

so i want to clean the logic board again, it all appears to be clean and i cannot visibly see any residue or oxidation even under magnification, therefore i expect there must still be some hidden beneath a component somewhere.

based on the problem i have described, is anyone able to help me locate physically where abouts on the board i should be focussing my efforts? i feel quite confident in working with these old 2006-2009 polycarb macbook boards, but my electrical knowledge isn't sufficient to figure out what components on the board are responsible for doing what (bar the obvious i.e. cpu, gpu and northbridge).

thankyou in advance!
justin

Answers

  • Hi Justin! Thanks for the post, and sorry for the delay getting back.

    It sounds like our level of experience is very similar, and you've done most of what I would do. I too have a good knowledge of the boards in general, buy my abilities fall short when it comes to identifying subsystems and homing in on a specific component on the board.

    I would say, though, that the topcases on A1181s can be problematic, so you might try "jumping" the board by triggering the power-on pads, with the topcase completely removed, and see if that makes a difference. I think there's probably a link to a picture of this on the site somewhere, if you search for it. And trying this is assuming you have a solid light on the AC adapter plug -- if not, it's not going to power on.

    A bad RAM slot is the most likely culprit given the symptoms you describe, but it sounds like you have correctly tested both slots.

    Another cleaning couldn't hurt, but sometimes these things happen when a solder trace is cracked, and it intermittently connects, or does not connect, when the board flexes due to heat, pressure, etc. I have not tried this, but for as little as $200 you can get a "reflow oven" on eBay, which is essentially a toaster that heats very evenly. You "cook" your board, all the solder turns liquid and "reflows" back in place, in theory filling in the cracks, and causing the board to work again once it cools. This has always sounded like a nice general solution to try, but again, I haven't purchased one of these yet.

    Last but not least, AB Cellars is on this site occasionally, and he has a very substantial knowledge of board component repair, so maybe he will see this post, or you can send him a private e-mail.

    Thanks and good luck!

    John
  • Hi John, thankyou very much for responding and taking the time to make these suggestions. I have also in the past tried reflowing other boards, so I will give that a try with this one if I am unable to identify any further liquid spill oxidation on the board that can be cleaned. I have also tried "jumping" the power to the board with the pads but this has the same effect as the power button on the top case.

    I am also going to look into purchasing some electronics test equipment in the future such as an oscilloscope and multimeter; so once I have learned to use these hopefully I may be able to identify problem areas or components more specifically. This is probably a steep learning curve away though so once I have this equipment I shall return and hopefully speak to AB Cellars to see if I can get any advise on where to begin!

    Thanks again,
    Justin
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