Wednesday, December 7, 2011

Lenovo Thinkpad Edge 14 display problem

I was recently brought one of these units with a peculiar problem. The display would power off, seemingly at random. After some basic testing I discovered that I could reproduce the problem by pressing the enter or backslash keys though other combinations of circumstances seemed to cause this glitch to resurface as well.

I initially chalked this up to a damaged display connector that was coming loose but after disassembly I found there was nothing wrong with the connector or display cable. This led me to some other wild and ultimately fruitless theories so I turned to Google. A few hits in I found this thread which seemed to describe the problem, at least superficially. I think a lot of unrelated problems have ended up in this thread, but there was enough commonality that I kept on pressing. On page 3 of the thread I found this little gem by a user named jimtristate:

"I experimented with holding a (fairly weak) magnet in various positions next to the power button and figured out how to turn on and off the display. I'm now going to wait until the mystical black screen appears and see if I can turn the screen back on just with the magnet. This, I feel, will demonstrate that the magnetic switch is probably getting triggered."

I opted for a strong magnet (from a stripped HDD). Sure enough placing the magnet near the power button caused the display to power off and removing it brought it back. Then I turned the display off with the enter button, and again placed the magnet. When I removed it the second time the display came back!

Well, jimtristate was right: this appears to be a problem with the magnetic sensor. My theory is that some aspect of the physical geometry or wiring of the keyboard is causing an errant magnetic field to be generated or perhaps simply directed towards the sensor. I've disabled the lid sensor in Windows and removed the Lenovo Power Manager with no effect. I'm unsure if this can be fixed short of removing the hall effect sensor / reed switch which controls this functionality.

**UPDATE** The aformentioned jimtristate at the Lenovo support forum updated the thread with the fix he discovered. He said he simply placed about 5 layers of electrical tape below the keyboard approximately where the P key would be and this seemed to solve the problem. I gave it a go:
and sure enough it works! Problem solved. This lends further credence to my theory that a magnetic field is leaking up from somewhere below, perhaps the HDD?

1 comment:

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