No Backlight After LCD Replacement

[The Spirit of X21]

I have replaced the LCD in my T40 with a known working LCD from a T41. I can see the video on the LCD, it is just not backlit. Is there something I should check?

[Harryc]

Did you replace just the panels or did you replace the entire lid assemblies with cables, inverters, etc intact? What was the screen resolution of the T40? T41?

[The Spirit of X21]

I replaced the whole assembly, cables and all. In fact, the assembly arrived as one unit - I just dropped it in. It's an XGA display.

[Harryc]

Did you see it working?

[The Spirit of X21]

No, but it came from a reputable member ( a mod).

[Harryc]

Well, I'll let that mod work with you then. There is no reason it shouldn't work if you replaced the entire assembly. Try reseating the LCD connector.
http://forum.thinkpads.com/viewtopic.ph ... &hilit=lcd

[The Spirit of X21]

Sure, will do. If I may, has a lack of backlighting ever been observed as a symptom of a bad GPU? I'd like to rule out my options...

[Harryc]

Well, let me ask you this... What was the problem with the T40?

[The Spirit of X21]

It started when the backlight went off and would not come on after rebooting the machine.

I tried replacing the inverter - that did nothing.

I picked up a couple CCFLs and soldered them: no luck (though I admit I am not very good with a soldering iron).

Now, I have tried replacing the LCD, only to find nothing at all.

It outputs to an external monitor quite well, it's just the stupid backlighting. Could it be a power issue? Is it possible that somehow the CCFL is not getting enough power from the motherboard? I would normally think that it's the backlight, but I'm starting to wonder...

[Harryc]

I think you might have blown a fuse on the systemboard. There are a couple dedicated to the LCD. Do a forum search for posts by a member named poshgeordie. There is a link in his sig to fuse locations. You'll need a multimeter for continuity testing.

[ajkula66]

I'd go with Harry's theory about a fuse being blown...however, if that is not the case, then you do have a GPU problem, because signal outputs to LCD and external monitor are separate, and one can work perfectly well while the other is shot...

Good luck.

[poshgeordie]

You'll need to check fuse F7 which can cause symptom you describe.

The document HarryC's referring to is T40 Fuses.

I've found a source for the fuse in single units in the US and it's here from Allied.

Please note though that the part number is slightly different to Shurter's data sheet and the one I suggest but will work OK (I'm going to do a complete overhaul of this document, so will also sort out this difference at the same time).

[The Spirit of X21]

I opened my T40 up tonight and tested the fuses located on the upper left-hand corner of the motherboard, where the LCD video cable attaches to it. Indeed, fuse F7 is blown. I guess I'll be ordering some fuses.

Anyone have any good tutorials on surface-mount soldering?

[poshgeordie]

This YouTube video explains it well - the first part shows how to solder a surface mount resistor so is relevant to you. Also towards the end he shows how to remove the resistor.

[RealBlackStuff]

If there is room enough, I would solder it piggy-back style over the old one.

[The Spirit of X21]

I just soldered the new fuse on. The unit now powers up for 5 seconds and powers off. This behavior can be repeated by removing the battery and AC adapter, then plugging in the AC and turning the unit on.

I ran a check with the multimeter, and it appears that fuse F??a (500mA) is blown.

Sigh...