2.26 or 2.4 GHz / White plastic unibody enclosure

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Logic Board won't power up; where to start?

I buy broken MacBooks and try to refurbish them. I don't do it to make money, really, but more of a hobby. If I can repair one to working condition and make a profit, great, but I certainly don't buy a machine with the assumption it will be an "easy fix".

That being said, I have a number of these 2009/2010 MacBook Unibody (model A1342) machines that have had various issues (liquid spills, no power, etc). I've gotten to a point with a few of them where I simply cannot find any problem with them. I've tested the top case/power buttons to ensure their functionality. I've checked over the logic board with a fine-tooth comb and have found no signs of liquid damage or burning. I cannot get the board(s) to power on even with a manual jump (using a known-good magsafe board and known-good charger). All boards receive power fine (and all will even charge batteries when attached). They simply won't power on.

My question (after all of that backstory) is: Where should I go from here? I could of course take a known-working logic board and compare/test each component with my volt meter, but with 10+ boards that would take a while. Is there a particular part of the circuitry I could start with--perhaps a "power on" circuit? Is there some main power fuse or gateway that I should check after confirming the top case and DC-in board are working fine? Is there anything obvious that I could be overlooking (something similar to not having the top case ribbon cable unplugged, etc)? I realize that sometimes the logic board can just be "dead", but certainly there's always some particular cause for failure (even if I can't identify is visually).

If I failed to provide any pertinent information, feel free to let me know! Also, if there's someone who specializes in troubleshooting this particular model, I'd love to pick your brain about a few things (in general) regarding the A1342 via email. Let me know! Thanks in advance for any replies.

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There are 4 pins at the flex cable connector of the keyboard case that goes to the slot at the Logic board. Problem might be that the flex cable of upper case with Keyboard became faulty. Now, to isolate it, short circuit between right 2 and left 2 pins of the keyboard connection slot residing on Logic-board with a pair of tweezers. Be careful not to short anything else that may fry the logic board. If this act starts up your unit, replace the upper case with keyboard. Otherwise, the problem resides somewhere else and we will be discussing on that later.

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Thanks for the reply, Puru. I will try that method of power-on this evening and let you know if that worked for any of them. As a pre-thought, before I try the pin-short method, what is the difference in that method of powering on and simply using the power pads (on board above the keyboard ribbon connector) to power the logic board up? Just curious.

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Steven will be eternally grateful.
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