MacBook Pro Oddity
by Jimmy Greystone - 9/24/10 5:40 PM
I spent most of my afternoon trying to noodle this one out, not really expecting anyone here to be able to help, but who knows. Sometimes people have a way of looking at things that I never would have come up with.
Have had a number of MBPs come across my workbench the past few months... Maybe 4-6, I don't really keep track, that have the rather curious and annoying habit of powering themselves on when the AC adapter is connected. And to rub some salt into that wound, they like to reboot rather than shut down when you press the power button. Only way to shut them off is to hold in the power button.
AFAIK, this has been happening with both 2009 and 2010 MBPs. All 13" if memory serves, but there may be a 15" in there. Rarely get 17" models, so I'd probably remember that.
So this afternoon, I replaced a logic board on what is turning out to be a real turd of a system. Initial logic board wasn't distributing power, system wouldn't boot. Replace that, then find that the trackpad is garbage. The Ts0P sensor is bad, and the trackpad itself gives erratic movement. I get the new logic board in, notice the fan going full speed so I know the Ts0P sensor is bad after having just fixed that on another system yesterday.
Anyway, I find that, even if the bottom cover isn't screwed on, just the weight of the laptop sitting on it is enough to cause some kind of a short inside the case that makes the system power on unexpectedly. Flip it so that the system is resting on the display, and take that cover off, it doesn't happen.
After spending maybe an hour playing around with it, I found I can pretty reliably trigger the system powering on by pressing on any part of the bottom case that is over the logic board.
So far I've tried replacing the magsafe board with another system's, because it will only happen if AC power is connected, that had no effect. I've tried a different bottom cover from another system, in case one of the grounding pins on the logic board was hitting metal because of a badly placed sticker; nothing. I made sure that the JST connectors for the speaker and microphone were both covered with electrical tape. I made sure the magsafe cables weren't pinched or that the shielding had frayed. Besides, replacing the magsafe board should have solved it if that were the case. It doesn't seem to matter if the keyboard and power button are connected, it will still power on. I tried disconnecting the battery, nothing, and the trackpad (since it's bad), and still nothing. I made sure the heatsink screws were all in as far as they could go without risking cracking the cores, nothing, and they should be electrically grounded anyway.
There is no one section of the case which triggers this behavior. Any area over the logic board can and will trigger it.
Now, this may just be my imagination, but it does seem like all affected systems have a pretty similar serial number. Like all of them end in ATM. So, I can't rule out it was just a bad batch, and the retailer I work for just happened to buy a bunch of those and distribute them to various stores.
In the past, I've generally just replaced the top case and that generally seems to fix things. However, that is a very time consuming and laborious process. You have to literally rebuild the entire laptop. And the entire underside of the top case is covered in a EMI shielding material which is also electrically inert. So I'm skeptical to the idea that there is some kind of a short happening on the underside of the logic board, even though that is what all the evidence seems to be pointing to.
So hoping that either someone here will have solved this issue or will say something that sparks an idea that solves it. I am now officially taking suggestions for things to try on Monday when I get back to work.