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HP 6720s Display switch mystery

Last response: in Laptop Tech Support
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a b α HP
a b D Laptop
January 12, 2013 3:07:26 PM

Removed switch cover and keyboard to clean dust from fan, but on re-assembly no display. Noticed I'd disturbed the Display Switch Assembly, re-seated it, still no joy. Obtained a replacement in case it was damaged, same result. Problem is I can't see for the life of me how it actually switches anything! There doesn't appear to be anything on the hinge assembly that affects the switch assembly in any way. As far as I know nothing has dropped off. Below screenshots of Hinge assy and Sw Assy.
Can anyone throw any light on the subject?







I don't see any moving parts on the Sw assy, no switches at all!
a b α HP
a b D Laptop
January 12, 2013 4:34:29 PM

could you have put her back in reverse since the cable should pass in between the uppper slot on your picture ?
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a b α HP
a b D Laptop
January 12, 2013 4:46:56 PM

scout_03 said:
could you have put her back in reverse since the cable should pass in between the uppper slot on your picture ?

Cable sits quite happily in the slot, and the cct board won't fit any other way in the bracket. As for the operation i wondered if there is a magnet in the hinge which triggers something in the switch mechanism when the lid is shut. Doesn't explain loss of display with lid open, though...
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a b α HP
a b D Laptop
January 12, 2013 4:49:25 PM

did you try to press the switch with the lid open to see it display stay on .
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Best solution

January 12, 2013 4:53:37 PM

Sometimes they are magnetic. Is there a magnet or a chuck of metal in a corrisponding location on the screen. So when you close the laptop the magnet triggers the switch and it goes to sleep?
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a b α HP
a b D Laptop
January 12, 2013 5:09:40 PM

Seems it is magnetically operated, there is a magnet under the bezel above the hinge cover. Either I have two duff switches, or the GPU has finally died due to the laptop overheating when a lump of dust jammed the fan blades....
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a b α HP
a b D Laptop
January 12, 2013 5:31:12 PM

scout_03 said:
link to service manual if it could help http://bizsupport2.austin.hp.com/bc/docs/support/Suppor...

Have the manual thanks all the same. I've had a few of these through my hands, nice 'tops if a bit dated now. Looks like I'll have to strip for spares, annoying as I just bought a new k'brd and switch panel as the originals were a bit rough!
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a b α HP
a b D Laptop
January 12, 2013 5:39:50 PM

Does display work through an external monitor? Can you press the switch and turn it on?

If all those don't work, does it have an Nvidia chipset or Graphics in it? HP's and Nvidia has a huge problem with lead-free solder and their chips, so much so, there was a class action lawsuit against it.
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a b α HP
a b D Laptop
January 12, 2013 5:52:10 PM

getochkn said:
Does display work through an external monitor? Can you press the switch and turn it on?

If all those don't work, does it have an Nvidia chipset or Graphics in it? HP's and Nvidia has a huge problem with lead-free solder and their chips, so much so, there was a class action lawsuit against it.

Tried an external, no joy. It's all Intel, so I'm a bit surprised that the GPU wouild fail, especially as it was turning itself off after a few minutes according to the owner. Should I spend another £3.50 on another switch...
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January 12, 2013 5:56:36 PM

Could you have messed the power inverter for the LCD? They die pretty often. Try plugging in a normal computer monitor to the vga and see if you get anything. That would show you that the computer is working and the issue is with the display.
If the regular computer monitor works, then chances are the inverter is bad.
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a b α HP
a b D Laptop
January 12, 2013 6:11:50 PM

bucknutty said:
Could you have messed the power inverter for the LCD? They die pretty often. Try plugging in a normal computer monitor to the vga and see if you get anything. That would show you that the computer is working and the issue is with the display.
If the regular computer monitor works, then chances are the inverter is bad.


Tried that, blank screen, so it's either the lid switch or the GPU.
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a b α HP
a b D Laptop
January 19, 2013 1:35:01 AM

Best answer selected by dodger46.
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