T23 screen backlight, inverter, motherboard or cable problem

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David749 · #1 Post by **David749** » Mon Dec 17, 2007 3:44 pm

Southampton, England calling
My daughter's T23 2647 HJI works fine on an external screen but only has a very very dim display on the internal screen. I tried a second hand replacement inverter from ebay, downloaded a video update and have toggled the function keys from internal to external to blank screen but no change. When it developed she had to open and close the lid several times to get it to work but then that stopped altogether. There was no evidence of any reddish discolouration at any time. The screen describes itself as 1024 x 678 TFT LCD panel.
If the backlight is gone can there be any display on the screen? And if the cable was worn could it carry a dim image or would it just carry no image? Can inverters be tested by amateurs?

Any help would be just wonderful

david749:?:

#2 Post by **rkawakami** » Mon Dec 17, 2007 4:34 pm

Welcome to thinkpads.com!

David749 wrote:If the backlight is gone can there be any display on the screen?

Yes, the only thing that the backlight and inverter do together is to light up the display. The pixels themselves will continue to work.

David749 wrote:And if the cable was worn could it carry a dim image or would it just carry no image?

Depends upon the damage. You could have a situation where the voltage gets to the inverter to drive the backlight, but some of the video signals are cut off and you no image on a "bright along the edges" display. Conversely, you could have a perfect image (shine a bright torch on it from an angle) but the backlight doesn't work.

David749 wrote:Can inverters be tested by amateurs?

Somewhat. Read this thread: http://forum.thinkpads.com/viewtopic.php?t=48910

edit: I was rushing out of the house to get to work so I missed one point that was brought up: "opening and closing the lid seemed to help". That might point to a bad lid switch. It's located in front of the right hand side hinge cover, just to the left of the battery LED. If Windows has been told to "do nothing" when the lid is closed (i.e., not go into standby or hibernate modes), then that switch can cut off the backlight while letting the system run normally. Opening and closing the lid may help to get the switch to operate properly. Since you have already tried another inverter I would have to bet that the backlight is your problem. If bad, the inverter WILL output enough voltage/current to try and light up the backlight (the neon bulb test that I described in the thread referenced above will turn on for a second or two), then the inverter will shut off. Another test would be to locate somebody near you with a T2x system like Robbyrobot has suggested and put your original inverter (and the replacement) into that system and see if it lights up the borrowed display. If both inverters work, then the problem could be with your backlight, cable or motherboard. Swapping complete lid assemblies (LCD, cable, backlight) will eliminate the motherboard as an issue. Then it's a matter of trying different LCD and cable combinations.

Robbyrobot · #3 Post by **Robbyrobot** » Mon Dec 17, 2007 4:36 pm

Generally something like this is due to a defective inverter, a bad backlight (CCFL tube in the panel) or a problem with the display cable. Unfortunately, I have experienced something similar on a T21 (at times, opening and closing the lid would light the display) and it was apparently due to a mainboard defect, since even a known good display (panel, cable and inverter combination) had no backlight on the board.

But to answer your questions...

If the backlight doesn't illuminate the screen, you see a dark image on the screen that you can make a little more visible with a bright light. That means there's a video signal coming through, but something is stopping the backlight from lighting.

A worn cable could either carry an image or none, depending on where the break was. There's no easy way to tell except trial and error (replace the cable with a known good one). And inverters can be tested - Ray (rkawakami) has described a procedure where you hold an NE-2 neon bulb close to the inverter on the display, and if the bulb lights, the inverter is good. I see he's already replied with the link.

It's hard to tell you exactly how to proceed, since my first thought would be to take the easy but more expensive route and buy a known good display. But then there's the possibility that there's a problem with the mainboard and you're out the cash without having a solution.

Do you maybe have anyone in your vicinity who has a T2x (T20-23) and might let you swap in the display just to test? That would be the best way to go about this, and the cheapest.

jamerslong · #4 Post by **jamerslong** » Mon Dec 17, 2007 6:17 pm

imo, i woud try to Jump the Lid switch, it is easy and should'nt hurt the computer, but usually the switch is stuck in the down position.

phool@round · #5 Post by **phool@round** » Mon Dec 17, 2007 9:17 pm

My first impression was stuck lid switch. You have some great answers and suggestions to work with so I'll stay out of the fray......

David749 · #6 Post by **David749** » Tue Dec 18, 2007 12:09 pm

Thank you everybody. I am overwhelmed by the generosity of spirit and time and thought of these responses. I have not yet tracked down a neon bulb and I need to learn how to take apart the main assembly.
There does seem to be something odd about the hinge switch which when depressed, very occasionally switched off the external screen but left the dim image on the internal screen. Would Ray's test for the inverter still work if this switch is defunct? The power to and from the inverter presumably comes through the cable?

David

#7 Post by **rkawakami** » Tue Dec 18, 2007 1:23 pm

If stuck in the "down" position, the lid switch will cut off power to the inverter so the neon bulb will not glow when placed next to the inverter. Power to the inverter does indeed travel along the ribbon cable. The backlight from the LCD plugs into the right end of the inverter. On the T2x systems, that's just to the left of the right side hinge. If you don't have it already, for instructions on how to disassemble your system, refer to the Hardware Maintenance Manual:

http://www-307.ibm.com/pc/support/site. ... UYM3F.html

All that is needed to take apart the system is a small (#0, I think; can't remember exactly which size it is) Phillips screwdriver. Tweezers or needle-nosed pliers can also help you to extract/install some of the screws that are recessed. An Xacto knife is handy for removing any of the round/oval/rectangular plastic screw covers, but a thin, flat-bladed screwdriver works too. Put the screw covers down on a piece of waxed paper so that they keep their "stickiness". Above all, keep the screws separated by whatever item they hold down. On a T23, most of them are obvious where they go because of the length. Some other systems can be fried if you attempt to use the wrong (longer) screw. I find that by using a desk drawer organizer or sectional utility box I can keep the screws and small parts together (and identified). As you know, to get at the inverter only requires the removal of three screws. If the problem is with the lid switch and it requires the replacement of the I/O board that it is mounted on, then you basically have to take everything out of the base (Ultrabay and motherboard).

jamerslong · #8 Post by **jamerslong** » Tue Dec 18, 2007 7:37 pm

You might be able to replace just the Switch, i belive i have seen switches on the 600's replaced at a cost of around 3$ for the part and some filing. it may be possible to do the same here providing you can find the compatible switch. Me personally i find the switch to be useless as i don't close my lid unless i have it plugged in, at witch point i would just solder the Switch to the closed position, just my .02

#9 Post by **rkawakami** » Tue Dec 18, 2007 8:30 pm

jamerslong wrote:You might be able to replace just the Switch, i belive i have seen switches on the 600's replaced at a cost of around 3$ for the part and some filing.

I believe you are referring to my post from last year:

http://forum.thinkpads.com/viewtopic.ph ... 349#168349

That 600X switch is fairly easy to replace as it uses "through-hole" soldering. I believe that the one on the T2x I/O card is surface mount. I haven't tried looking for one but it might be available from either mouser.com or digikey.com. And if you don't even need to USE a switch, then simply remove it, find the pins that are normally closed and then solder wire(s) to those places on the I/O board.