LCD backlight burn-out?

[Rex]

Hi there,

I have read lots about the appearance of an LCD backlight burn out. Dull, flashes, uneven illumination, colour fringing. etc.

My T20 screen does none of those. The screen backlight is frequently not coming on when booting but it can be enticed to do so. Occasionally, after about 1/2 an hour of running just fine, it will fade out over a 10 second period. Once again, it can be enticed on and then there appears to be no problem for the remainder of the session.

Is this a symptom of backlight burn-out? Is it worth replacing the laptop's LCD screen or should I buy a new backlight and replace just that one component? I have already eliminated the Inverter and screen cable by replacing them.

Really grateful for any suggestions.

Many thanks,

Rex

[rkawakami]

Occasionally, after about 1/2 an hour of running just fine, it will fade out over a 10 second period. Once again, it can be enticed on and then there appears to be no problem for the remainder of the session.

How exactly are you "enticing" it ?

A couple of things to check/verify before ordering another LCD panel or trying to replace the CCFL...

WIth the laptop turned off, press down several times on the lid closure switch in front of the right hinge. If the switch is broken/dirty it may be causing the loss of power to the display. Power up and see if that helps.

Remove the bezel to the LCD and check the wiring to the backlight. There could be a loose connection. This would be the wires from the inverter board to the lamp.

The easiest thing to do if that doesn't work is to replace the entire LCD panel with a known good unit. It is a lot more expensive than just the CCFL (about USD$20 on eBay) but you won't have to deal with prying apart the panel just to get at the lamp. Some lamps are easier to replace than others.

[Rex]

Ray,

Thanks for your reply.

I'm convinced the lid button sticking is not the problem. Could be a factor with the 'blank' screen on booting, but I can see a faint 'ghost' image during booting so I figure the pixels are working.

And the lid button would not explain the sudden occasional blanking of the backlight when it is up and running.

Don't think any of the connectors are the problem as I have dismantled the screen twice to replace the LCD cable (made no difference) and the Inverter (also made no difference.)

However, during reassemble, and before everything was screwed back, I booted it any number of times and could not produce the 'blanking on booting' problem, so figured that I had fixed it. But the first time I booted following tightening all screws, the problem was still there. It almost seems as if there is a pressure point on the screen that is causing the backlight to occasionally switch off.

To make the screen work, I open and close (not fully) it. After a few seconds of doing this there seems to be a position where the backlight comes on; just like a contact has been made.

Hence, I am still convinced that my problem is the backlight tube, but unless I replace something, I will not know. Certainly, replacing the tube is the least expensive option but also the more difficult.

Rex

[rkawakami]

But the first time I booted following tightening all screws, the problem was still there. It almost seems as if there is a pressure point on the screen that is causing the backlight to occasionally switch off.

To make the screen work, I open and close (not fully) it. After a few seconds of doing this there seems to be a position where the backlight comes on; just like a contact has been made.

Sounds suspiciously like a loose wire or bad contact to a terminal on the backlight. If you can follow the pair of white (?) wires coming off of the inverter board that should lead you to the backlight. I replaced an inverter on my newest T23 about a week ago to fix a permanently dead backlight but I don't remember if you can get to the backlight leads without removing the entire panel from the lid.

[Rex]

Ray,

No problem in removing the screen. Have done so a number of times (and cracked teh screen bezel in the process!)

I tend to think that it is either a faulty backlight, or as you suggest, a bad connection within the sceen assembly.

Rex

[kass73]

When you are having troubles, try opening the screen to an obtuse angle and pressing lightly on the LCD cable. Can you entice the screen to light up . I had this happen with a T21. If so, I guess it's a bad cable or cable connection I guess.

[Rex]

It is an obtuse angle that makes it jump to life. But more recently, it takes some effort to make that contact. As for the cable, that has been replaced.

Interestingly, when I was replacing the screen cable and inverter, I booted the computer before screwing everything back together. Every boot, the screen worked as it should. Thought I had cured the problem so replaced all the screws and the problem returned!

It is definitely the backlight, but why the above should happen, beats me.

Rex

[Rex]

Kass73,

Tried your suggestion and it does seem to work. Do you know of a permant fix rather than pressing the back of the screen every time?

I have replaced the cable but I don't think the old one was faulty.

Rex

[tfflivemb2]

If it was working each and everytime with the screen exposed, and then the problems came back after it was closed...I would check your connections, it sounds like something might be pressing on something to cause the light to go back out. Check where your CCFL wires are sitting. Make sure that a screw isn't pressing on them, possible causing a short.

[Rex]

tfflivemb2

Happened again tonight while watching a DVD. Pressing the back made no difference but adjusting the angle did.

I understand what you are saying and agree, but since there is only the ribbon cable between the screen and the case and the Inverter is along the side, I don't understand where my problem is. Have changed the inverter because of this problem and when I reassembled, the problem was still there. The chances of dismantling and reassembling with the same problem are not so great.

So I figure my next move is to replace the backlight (least expensive option) before replacing the whole screen.

Rex