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How can I test the  close cover switch on an HP zx5000 laptop

Posted on 2007-11-18
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Last Modified: 2013-11-17
I have an HP zx5000 laptop with a backlight issue. The laptop will work on an external monitor, and I can see the dim desktop on the lcd screen when viewed with a bright light at an angle to the lcd screen.
The problem is that while this seems to be a classic inverter failure, I can sometimes get the laptop screen backlights to turn on by pressing the small lid switch pin. This happens occasionally and when it does the screen will stay lit for 10 seconds and reverts to an unlit screen.
I am still thinking its the inverter, has anyone else seen this?
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Question by:Mark
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by:nobus
ID: 20310916
you can try to remove /reseat the video cable for the lcd
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by:Mark
ID: 20312136
Sorry, forgot to mention that was the first thing I did.
I would like to know if there is a testing method for the switch itself, as I'm not sure if I want to put a multi-tester on it to check continuity, as that applies power from the multi-tester when testing.(don't know if thats an issue)
 The switch also has four legs soldered to the motherboard, so its a guessing game which apply to the backlight.
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nobus earned 150 total points
ID: 20313016
you can connect a meter on 2 connections, and watch what heppens if the switch is activated
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by:Mark
ID: 20325183
I'm not comfortable doing that, I don't want to pick the wrong 2 and short the board, that would be an even worse situation.
I guess I'm going to have to go with my gut and replace the inverter. Stay tuned, it'll take a week to get the part. Not an easy on to find as there seems to be many models.
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by:garycase
garycase earned 100 total points
ID: 20325763
As I'm sure you know, this can be either the backlight or the inverter.   Notwithstanding the occasional functioning of the light, I'd still suspect the backlight => a bad fluorescent bulb will sometimes have just those symptoms.   I've got an old Dell Latitude with the exact same issue [haven't bothered to repair it -- I really have far too many PC's as it is :-) ].

... considering that new backlights are very inexpensive (usually < $20) I'd try that first :-)   It's a bit trickier than an inverter to replace ... but I'm confident you'll not have any problem doing so :-)

With any luck, that will be the problem.   If not, then it's time for an inverter => but the backlight probably won't be wasted, as it's very common for the backlight to fail when the inverter goes out.
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by:nobus
ID: 20326117
>>  I don't want to pick the wrong 2 and short the board   <<   connecting a meter will not short the board, but you need to be cautious (like in replacing the backlight)
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by:CarlosMMartins
ID: 20326323
It might also just be the lid switch acting up.
I've seen a couple of laptops with similar behavior after a they've been dropped.

If you're comfortable enough with electronics - as you seem to be - you could check it's outputs, see if any of it toggles as expected (press/unpress - on/off output)

Also, how old is the laptop? If more than 2 or 3 years, than the inverter/backlight is also a prime candidate as you yourself have said.
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by:Mark
ID: 20327637
Thanks for the posts.
I began thinking more about the backlights myself Gary, it would be more difficult than just the inverter but certainly not impossible to fix. Easy to test though, I have a backlight stripped from another lcd screen that I can hook up to the inverter for testing, that should be a definitive test of the  backlight at least.

Carlos, & Nobus. I would like to test the switch, and I'm going to come up with a method to isolate each of the switches legs and their purpose, but this is someone else's laptop and I am more cautious than if it was my own.

I'll be back.
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by:CarlosMMartins
CarlosMMartins earned 100 total points
ID: 20327969
Maybe by checking the power input at the inverter and see if it toggles according to the switch?
That's easier to find and test than the smaller pins at the switch circuit (at least for a first test)... :)

Also before mixing inverters and backlights, be sure they have the same characteristics... But I'm sure you don't need me to tell you that. :)
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by:Mark
ID: 20328035
That sound reasonable, I was trying to avoid a total stripping of the display as this model seems to have been superglued together by HP. I guess I don't have much choice.
Thanks.
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by:Callandor
Callandor earned 150 total points
ID: 20331986
I wouldn't worry about the voltage and current for continuity testing - testers typically use a single AA battery.  Though some electronics are sensitive to low levels, I doubt the circuitry for a switch that powers on the backlight is "delicate".
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by:Mark
ID: 20362335
Update. The CCFL's are good, the switch is good(tested with multimeter for continuity)
New inverter has solved the issue. I guess I was reading too much into the intermittent lighting  when the switch was activated. Inverter must have had a weak coil to allow it to light for the 10 secs then shut off.
Thanks all for the comments.
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