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Released June 2012 / Core i7 processor with Turbo Boost / Up to 1 GB DDR5 Video RAM

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Can I disable a broken reed switch / hall sensor

My MacBook Pro is having sleep issues that seem related to the hall sensor (often referred to as the reed switch), and I would like to know if I can solve the problem by physically disconnecting the sensor.

[A detailed description of the symptoms is below.]

I'd be perfectly happy if I could simply sleep / wake the machine "manually," with the clamshell open, and closing or opening the clamshell as appropriate without affecting the machine's sleep state. Is physically disconnecting the hall sensor possible? If so, would it accomplish this?


The machine will suddenly go to sleep while being used (and with the clamshell open). That is the big problem.

Also: if I close the clamshell with the machine awake, it goes to sleep. Then after a few seconds it seems to wake up. The sleep indicator light starts blinking rapidly (rather than pulsing slowly).

If I sleep the machine with the clamshell open (e.g. by selecting "sleep" form the Apple menu in the Finder), it will wake up after I close the clamshell.

Diagnostics / system info:

The main tests in Apple Hardware Test and Apple Service Diagnostics (both OS and EFI) show no issues, aside from a press of the battery indicator light button not being registered by the SMC. One of the interactive tests in ASD intermittently registers a problem with sleep/wake and the clamshell.

I have an SSD in the main drive bay, and I replaced the optical drive with the hard drive that came with the machine (using OWC's "data doubler" bracket). This problem did not crop up until many months after I replaced the optical drive with the hard drive.

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I suspect you have two issues here:

The first - When your system goes into sleep mode on its own its likely a SMC issue. Lets try resetting the SMC. Follow this Apple TN: Intel-based Macs: Resetting the System Management Controller (SMC).

In addition you need to check your battery. I would recommend this gem of an app: coconutBattery. Take a snapshot of what it reports and post it here for us to see.

The second: Sleep wake issues like you describe are often caused by background running processes.

Try this using an external hard drive which had a clean OS on it (nothing else) see if your system reacts any different. If it does you have some work to isolate out whats waking up your system.

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Thanks very much for your thoughts! Apologies for the delay in replying.

* I tested the battery using the application you suggested, and it is fine.

* I did confirm that booting a clean OS from an external drive does _not_ solve the sleep/wake problem.

* However, on further testing it seemed that tilting the entire machine sometimes solved the problem. Perhaps an out-of-alignment magnet in the lid was made to slide back into place by all of the testing. In any case, the sleep-wake problem now occurs much less frequently. However, there are still times when closing the lid does not cause sleep to occur, etc. Basically, the symptoms described in the original post persist, but are now much more intermittent.

Given all that, I'd still like to disable the switch completely if possible. I prefer the minor inconvenience of having to "manually" sleep the machine before closing (as opposed to the potential for the machine to "self wake" and drain the battery and/or overheat).

Anyone have thoughts on whether there is a way to adjust either software or hardware to disable the reed switch/hall sensor entirely? Playing with pmset and disabling clamshell sleep, etc does not seem to work.


Sounds like the sensor or the magnet is loose. The magnet is about half way on the left side in the cover use a paper clip to find it sliding it along the inside edge. Did someone replace the LCD or the cover glass? If not then its not something that should have slipped. The hall sensor is part of the battery tester just in front of the headphone outlet. To get to it you'll need to take the battery out. You'll find the other end of the battery tester/sleep sensor contacted to the logic board. Review this IFIXIT guide MacBook Pro 15" Unibody Mid 2012 Upper Case Replacement go to Step 18 to check the ribbon cable is firmly connected and inspect it for any damage and check to see if one of the screws worked its way out.


Thanks so much!

The LCD and cover glass have never been replaced. The battery indicator started working again, at the same time that the sleep/wake problem mostly resolve itself. So it sounds like the problem was likely on the battery tester/hall sensor end of things. Though I don't know how a loose ribbon cable could have gotten more firmly attached by itself.

One last question: could I just completely detach the ribbon cable you mentioned? Would that likely allow the MBP to function normally, except the battery indicator light and "sleep on close/wake on open" functions would be disabled?


Not sure what it will do with it disconnected connection (never tried) give it a try just make sure you don't let the loose end short across anything. Frankly, I would investigate the root issue a bit more Vs disabling the checker/switch to get around the problem. You may have a deeper problem here like a leaking battery or a loose screw holding the assembly. It could even be something was spilled which should be cleaned up so it doesn't cause more damage.


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