HP DV6915nr display won't light

wirefaninpa
wirefaninpa used Ask the Experts™
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I have a laptop that has been having problems with the display for months. I can see the images on the screen (especially with a flashlight) but the display is very dim.

At first the problem was that whenever the laptop went into the sleep state the screen would stay dim even when awakened. If I closed the lid and re-opened then the screen would light for a little while. Eventually it stayed lit so long as the computer didn't go to sleep. I stopped the computer from going to sleep at all and this solution worked for a few months.

But now the light has gone out again regardless of the sleep state. When I power on the computer or close and re-open the lid, the display becomes bright for about half a second but that's it. I disassembled the display and couldn't find any loose or untoward connectors. The inverter and everything looks okay. I think the sleep switch is magnetic so I can't mess with that (I have yet to find it). I can't figure out which component is causing the problem so I don't know what to replace.
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Commented:
There can only be 3 reasons for this 1st one is your inverter gone. Especially if it brightens up than goes off again. The other reason is your lcd display cable might be damaged or streched from its connection behind the lcd. 3rd one is your lcd screen. We repair around 15-20 of those kind of problems each month. I doubt if its the cable if it is the cable it will flicker as well as dimms down. You need to test it with another inverter or Lcd screen vice versa.
I reckon its the inverter.

Author

Commented:
Thanks for the feedback BPCC. I have an identical working laptop so I tried switching inverters. The working inverter in the broken laptop made little difference. On bootup the display lit for maybe a second longer than usual, then dimmed as always. Conversely, when I put the inverter from the broken laptop into the working laptop, everything worked fine (in fact, I am typing this message from that laptop using the inverter). Should I try switching LCD screens (assume I would need to try with a new cable, or can I switch those too)? Could it really be the LCD screen?

You said there can be only three reasons, but what about the backlight itself?
Commented:
Now your inverter is tested ok.
From your test it looks like it could be the CCFL.
The fact that the video is still there means the video signal is reaching the LCD.
Only it cannot be displayed out due to the failure of CCFL.

Its a challenge to change the CCFL and if the job is done successfully its really satisfying.
If your laptop is more than 4 years old its time to change the CCFL.

You must buy the right size of CCFL. If you are changing the CCFL the first time. Its better
to buy two CCFL just in case one get bugged up due to handling/installation.
CCFL cost between 9 to 10 dollars per piece. You may have to pay more for postage.

So time for you to look up at your service manual and get the right size of CCFL.

An easier solution is to change the whole LCD but that would be a costly affair.
So you have to decide the best option.
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Author

Commented:
Yeah, changing that will be a real challenge.  But I do like a challenge. I'm going to go ahead and try that just for the experience, and if it doesn't work then I will change the lcd display. There isn't any chance that this is a motherboard issue is there? It does seem power-related. I'd rather it not be, but is there any chance that changing the entire LCD display won't fix it?
Commented:
Yes that is the way forward to replace the CCFL.
But before you order your new pieces of CCFL, you should take out the CCFL.
Have a look at it. Most likely the end would have changed color to black.
I would recommend you to buy two CCFLs.

Note CCFL are very fragile and a slight mishandle would cause it to break.  
The tricky part is making  sure that the CCFL is mounted correctly and is infirm
contact with the thick plastic panel which conducts the light.

When you dismantle make marking on the side of the frame so that when
you reassemble the panel back you dont waste time in reassembly.

I find taking photo graph is also a good way to help you remember but markings
come in handy esepcially when the rectangular sheets are different slightly at the edges.

Once you get the CCFL test them first before you start to mount them on the LCD panel.

Good luck.
Top Expert 2013

Commented:
switch the whole lcd to test, or dismantle it for swapping the cable (which i suspect) : >>>>    When I power on the computer or close and re-open the lid, the display becomes bright for about half a second
Top Expert 2013

Commented:
another thought : check the lid switch also !!

Author

Commented:
I can't figure out where the LCD switch is on this thing.

Commented:
If you dont see a button near hinge or protrusion on the LCD panel near the hinges, it could be that that your laptop is using a magnetic switch. As mention by nobus this switch could also be in issue. In the cases with I had experience a faulty switch means no display.
Top Expert 2013

Commented:

Author

Commented:
After much examination I'm pretty sure this laptop uses a magnetic switch, but I can't figure out where that would be or what it looks like.
Top Expert 2013

Commented:
it looks like a little black box in most cases, i believe under the right hinge

Commented:
Just to be sure swap the whole LCD it and test as suggested by nobus.
It will involve some patient work and the test will confirm/rule out  if the magnetic switch is the cause to the issue. Really it will make sense to do the swap test before you decide to order CCFL.

Commented:
If swapping inverter made that difference I suggest you to swap the LCD. It is easier to dismental LCD and swap than taking the lcd cable out. Magnetic switches never will be an issue. They all had been tested by manufacturer at R&D (Research and Development) stage before they pass it on manufacturing. I will be very surprised actually shocked if its the cause. It would be a design fault too big for HP. Let me know thanks...

Commented:
Also on one of your comments you mentioned you think its power rlated if you had previous power supply dut off or dead and your battery is not fully charging it would damage the video card. All that CCFL and power related problems are a long shoot. Lets go through the common fault finding process on this kind of instances. Like I mentioned before poer CCFL etc is tested during R7D period actually hammered for consumer do not get that kind faults that easy.

Author

Commented:
It was the backlight; scorched on one end.

Author

Commented:
Thanks everyone. I replaced the backlight and now we're up and running. Not sure that's something I ever want to do again, but it was good for the experience.

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