failing backlight in t40 - is this the graphics failure

[5p33d0]

hi guys,

my t40 has been having a flickering back light for quite some time.
due to the need for the laptop i didnt remedy the problem, BUT kept turning screen off and on with the keyboard OR putting it to sleep and closing the lid to get the back light to work again.

now that i have time i took the top lid apart and as a result with the t40 naked the back light fails to com on at all...

has anyone experienced this? how to i solve my back light issue? is this the dreaded graphics problem?

thank you for your input.

[tomh009]

So your display is still working, right? Just without any backlight?

[5p33d0]

yes that's right.
the back light was flickering when the display was adjusted.
now that i disassembled the top lid to check for any disconnected wires the back light has stopped working.

[tomh009]

So either the backlight bulb is gone for good ... or there is a broken connection. Can you check for voltage at the backlight contacts?

[RealBlackStuff]

Just in case, check the sticky t42 shuts down when i move it.
Other possibilities:
- a faulty LCD switch, that's the tiny microswitch that shuts the LCD off (or puts the TP into hibernation, etc.) when you close the lid
- a broken LCD cable
- cable loose at rear of LCD panel

[bajaman61]

yes that's right.
the back light was flickering when the display was adjusted.
now that i disassembled the top lid to check for any disconnected wires the back light has stopped working.

One simple and fast test not yet mentioned is to connect the laptop to a second, known-working monitor. If the second monitor coupled with the T40's base works 100% then we can localize the problem to the screen and/or inverter and rule out the GPU. The GPU, being on the motherboard would malfunction regardless of where the video data is displayed. A 100% working base paired with a second working monitor rules out the GPU as suspect.

If it is not the GPU:

Replacing the inverter is relatively easy (but needs caution as there is a whallop of volts in that piece that can remain there when the system is not powered up, as the famous (and justly so) Ray K described in a previous post). Replacing the CCFL/backlight is something much more difficult but not impossible. Another option is to just buy a screen that works and plunk it in.

You did not mention a frequent tell-tale indicator of a failing CCFL/backlight: a pinkish hue on start up on the screen. Did you notice that when the system was working?

Knowing whether (1) the pink problem showed up, and (2) the base works with a known-working monitor, will help narrow the possibilities.

[RealBlackStuff]

unfortunately that's not quite true.
The GPU provides 2 signals, a digital signal to the LCD, and an analog signal to the external monitor.
Even if the external monitor works OK, the digital/LCD GPU-part may still be faulty!

[bajaman61]

unfortunately that's not quite true.
The GPU provides 2 signals, a digital signal to the LCD, and an analog signal to the external monitor.
Even if the external monitor works OK, the digital/LCD GPU-part may still be faulty!

I always learn something here. To push this further, the GPU problem as I understand it, is that the soldering "cementing" the GPU's base to the motherboard can partially detach. This poor physical connection causes any signals transmitted from the GPU to any device to become garbled or non-existant, with garbled or no data displayed on the monitor. I base this on the GPU "reflow" posts here.

Wouldn't any signal from the GPU be impacted by the poor physical connection of the GPU to the motherboard if the GPU/solder problem is to blame? Don't all signals from the GPU have to pass through the same (possibly weakened or broken) circuitry?

My interest in this is because repairing T4x's with the GPU issue is a hobby of mine. I do not wish to hijack the original poster's problem, but to learn about his/my favorite issue. So learning more about this is actually fun. Yes. Really.

[rkawakami]

This is getting slightly off topic, but to explain what might be going on with the external video working and the LCD not....

There's hundreds of solder balls underneath the "video chip" which connects it to the motherboard. There's also dozens more that attach the two memory chips to the "top" surface of the video chip substrate. Depending upon the positions of the solder balls which have come loose, you can have a minor failure which affects only the signals going to the LCD; the ones going to the analog VGA output could still be connected. Or, you could have a major failure which takes out the entire functioning of the video system; say a short between a power and ground solder ball. So it really depends upon which solder connections are at fault. From anecdotal evidence being reported here and at other sites, when the ATI GPU comes loose from the motherboard, it appears to mainly affect the LCD display and not the VGA port.

[bajaman61]

. . . Depending upon the positions of the solder balls which have come loose, you can have a minor failure which affects only the signals going to the LCD; the ones going to the analog VGA output could still be connected. Or, you could have a major failure which takes out the entire functioning of the video system; say a short between a power and ground solder ball. . . .

Thank you, Ray, now I better understand RealBlackStuff's information. To give some hope to the original poster:

how to i solve my back light issue? is this the dreaded graphics problem?

thank you for your input.

Another suggestion: As there is a chance it is the GPU, the procedure described in this How-To worked on two erratic T40s I had: http://forum.thinkpads.com/viewtopic.php?f=31&t=74366. I used an empty plastic Compact Flash container as a wedge instead of the cards used in the How-To. Two of the plastic container's corners were cut so as to be able to seat the wedge only on the GPU itself. The procedure outlined in the How-To took less than 30 careful, non-hurried minutes.

I recommend this only as a way to rule-in or rule-out the GPU as the source of the problem. After installing the temporary wedge my T40 booted perfectly and ran all applications normally. Previously it displayed symptoms similar to those you describe. With the temporary wedge installed I ran the T40 through a power-on, use applications, access internet video, power-off cycle 5 times in short succession. Then over the next few days I tested the machine randomly, leaving it on or off for several hours straight. Worked 100% at any time, all of the time.

This procedure answered the question about the GPU's role fairly easily.

If it turns out that the GPU is innocent, then the temporary wedge can be quickly removed with no permanent change or harm to your machine.

If the GPU is guilty you have several (non-dreadful) options: (a) paying a service to reflow it (there are some services on this forum that do this at a reasonable cost and that have feedback from forum members); (b) reflowing the GPU yourself following the "sticky" in the T4X subforum; or (c) swapping in a "near twin" R51 motherboard (that I believe has a different GPU chip).

Let's save this T40.

[5p33d0]

okay let me reply in order from my last post:

can i check for voltage?
yes i can - but i dont know where the back light contacts are

t42 shut down link- i will take a look on the weekend.
as for shut down switch... need to know where those are.
bad/loose cable- would love to know which cables these are to test if they are connected/damage

laptop to another lcd- works fine )
also no blue or other color hues. therefore could be the back light and not the inverter

i have no comments on the off topic reflow posts but thats good back ground info.
I hope i am okay and this is a screen issue.
BTW i have a 14" t40

Asfor the suggestion to use the CF card case wedge- there is no change when i add or take away pressure on the gpu
historically when the lid was moved thats when the backlight fails.

a service i found for reflow costs 150$ CAD for me. i wish to avoid thsi due to this computer being old and basically a rugged road warrior for school notes.



so for now could anyone point me to a diagram of the cables( ie what page in that handbook for repair is it) and also where should my test points be for back light contacts and what should the voltage be. is it any number above zero??

[bajaman61]

okay let me reply in order from my last post:

can i check for voltage?
yes i can - but i dont know where the back light contacts are

The "backlight contacts" are two ends of a very thin florescent light bulb. (Search for "Cold Cathode Florescent Light" or "CCFL" if you want to get an idea of what these look like.) The contacts of the CCFL, one on either end, are embedded along with the blub itself in the screen assembly and are not easily accessed. To access them you would have to open the LCD assembly, then cut tape and pry apart a metal and plastic casing that binds the layers of screen together with the small metal casing that houses the CCFL attached at one end of the screen assembly. This is not easily done directly at the CCFL's contacts. These contacts are soldered to two wires that connect to the inverter which is more easily accessed but can hold a very high voltage, SO I DON'T RECOMMEND TESTING THE BACKLIGHT'S VOLTAGE as your question implies.

I don't think testing a bulb's voltage is what you want to do anyway -- what you want to do is connect the bulb to a known working inverter with proper grounds. It lights and stays that way or it doesn't -- that is the test you want, right?

Also, I would not recommend opening up the LCD screen and replacing the bulb unless you have done a few already. It is likely better and more cost efficient to buy a replacement screen or parts machine if the screen and not the GPU is found to be the problem.

t42 shut down link- i will take a look on the weekend.
as for shut down switch... need to know where those are.
bad/loose cable- would love to know which cables these are to test if they are connected/damage

The words "shut down switch" can apply to at least two different things, but I suspect that what you mean is the switch that can be activated when the laptop is closed while it is on. The T40 has a small outcropping on the screen bezel located on the computer's lower right portion. A complementary declivity on the base bezel contains a small switch that the outcropping pushes/activates when the laptop is closed. That is probably what is being discussed.

As for "bad/loose cable" you probably mean the screen cable that connects the the motherboard to the screen. The Hardware Maintenance Manual for the T4X line can be found here: http://www-307.ibm.com/pc/support/site. ... MIGR-46464 This will show you exactly where all the parts are. The connection to the motherboard is easily accessed as it is in approximately the middle of the motherboard. If that connection is not seated properly then it can cause a loss of or poor screen display. The integrity of the cable itself should be checked as far as possible from the motherboard up to the point where it disappears into the screen housing just beside the T40's right hinge. The cable connection inside the screen housing is not easily accessible for the same reasons as the CCFL's contacts are not.

laptop to another lcd- works fine )
also no blue or other color hues. therefore could be the back light and not the inverter

AHHH, so this can help narrow things somewhat. A red color often heralds a dying CCFL, but if you have a good picture on an external monitor we know at least that the portion of the GPU that sends a signal to the external monitor is working. If this is repeatable then that is good information.

i have no comments on the off topic reflow posts but thats good back ground info.

The reflow posts are not "off topic." Reflowing is one way to fix a bad GPU. You raised the "dreaded" GPU problem as a possibility. Given the T4X's history and that problem's rough conformity with the symptoms you described that problem and its solution should certainly be entertained as a possibility. Since we do not know what the problem is with certainty, we cannot say what the problem is not.

I hope i am okay and this is a screen issue.
BTW i have a 14" t40

We can hope that is the case and it is possible but not yet certain that it is. That is why we need to keep in mind all possible diagnoses/solutions.

As for the suggestion to use the CF card case wedge- there is no change when i add or take away pressure on the gpu
historically when the lid was moved thats when the backlight fails.

If you are applying pressure directly (not as some people do -- by pressing down on the keyboard) then this looks less like the "dreaded" GPU problem.

a service i found for reflow costs 150$ CAD for me. i wish to avoid thsi due to this computer being old and basically a rugged road warrior for school notes.

Shop around, I recall reading posts that had satisfactory results for less than half that cost. But that assumes the GPU is the problem, let's be sure first. Didn't you just say reflow was off topic? You are trying to confuse me, right?

so for now could anyone point me to a diagram of the cables( ie what page in that handbook for repair is it) and also where should my test points be for back light contacts and what should the voltage be. is it any number above zero??

Download the HMM at the link provided and the index therein will show you many helpful pages. The other part of this question is answered above.

Good Luck.