General discussion

connecting macbook battery causes backlight failure,etc

This unit starts up & runs normally with power adapter connected but if I connect a good battery,the display goes black & the sleep light blinks. I've connected an external monitor with only the power adapter & both the external & the macbook's display are fine. Again, once I connect the battery I have the external showing the desktop but there's no response when I click on any files or move a window, although I do have cursor movement. The MacBook display is black.
I've read in other discussions, that changing the inverter board, reinstalling the operating system, etc didn't work.
Please let me know what you think.

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First off

First off, are you SURE it's a good battery? What you describe sounds very much like there's a grounding fault.

The inverter board wouldn't have anything to do with this unless it also failed while on only AC power, so that one's out, and same with the OS restore. The symptoms should persist regardless of power source.

If it's not the battery, my guess would be the battery connector/sleep switch. That could very well have gone bad and so when you connect the battery it somehow manages to put the system into a quasi sleep state. That part is really very cheap to get, and not even necessarily all that difficult to replace, so it would be a good place to start if you feel comfortable enough to remove the top case and take a crack at it. Just make sure you keep track of which screws go on which side of the MacBook, because the left and right sides use two different screws, and if you put one in the wrong spot, you're never going to get it out again without breaking it. One of the tricks I use, is to lay the screws out in a pattern resembling their location on the part I'm removing. And a post-it telling you which part those screws came from could be handy as well. Hopefully you never take so many of those units apart, like I do, that you pretty much have every screw and it's location memorized.

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Battery is good

Jimmy,

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That doesn't necessarily mean anything

That doesn't necessarily mean anything. The battery could be bad, and have been slowly damaging your system until finally it crossed a threshold where it's too far gone to be able to take that kind of abuse anymore. Another system might well still be able to withstand it.

It's not exactly a sure fire test, but take the thing into an Apple store when you get a chance, have them run the battery diagnostic part of AST on it. If it tests bad, then you know you need to replace it.

Just out of curiosity, since you appear to have access to a second system of a similar nature, have you checked to see if the symptoms persist using a different battery from yours? I just assumed you didn't have access to another system with my initial post, but since you do, I would definitely give that a try. If it's just a bad battery, maybe a minor grounding fault or something, that's a non-invasive repair. Quick and easy, no need for a screwdriver at all. If the symptoms persist, then you can move on to replacing the sleep switch. If that doesn't fix it, then I'd say odds are your logic board is on its way out, so just use it on AC power until it finally craps out, then get a new one.

The somewhat unfortunate thing about the sleep switch, is it's just a small PCB with metal pins that run right through the logic board. So it's easy for an issue affecting the sleep switch to spread to the logic board proper. Which brings us back to if replacing the sleep switch doesn't solve the problem, it's probably the logic board, and that will likely run you almost as much as a brand new laptop.

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no luck with sleep switch replacement

I put a working battery into this unit & it did the same thing. I'm certain it's not the battery.

The sleep/switch replacement part finally arrived, I put it in but the same problem persists. Is there anything else I can try? How do I determine if it's in fact a logic board problem? I'm thinking of bringing it in to a genius bar, discuss the problem & tell them what I've done so far. Will they still test it even though I've opened it up & replaced the switch?I want to thank you very much for your feedback.
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You already have

You already have proven it's the logic board, unless you want to rethink the possibility of it being the battery.

You've seen the inside of the thing, so it should be pretty obvious. The battery connector plugs straight into the logic board, and it's physically located in it's own little area of the logic board, on the opposite end as the magsafe board, which has nothing to do with whether or not the battery is detected.

So if replacing that cable didn't do it, and we're assuming you've ruled out it being a DOA part, then you move on to whatever is connected to it, which would be the battery on one end and the logic board on the other. One of those two things is bad, assuming you didn't just get a DOA cable.

If it were me, I'd first try another sleep switch. If that doesn't work, then if you're still certain it's not the battery, it would be the logic board.

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