T21 display problem

[lather]

I've got a bit of a problem with a T21 that I'm hoping someone here can help with.

A little while back, my Dad asked me if I could fix the T21 that he uses as his home recording studio to make CDs of him playing the organ that he gives out as gifts to friends who like that kind of music. All he told me was that it wasn't starting up, the screen was blank, and it made a few funny bleeps when he tried to turn it on. He also told me that, for a while before it died on him, he was having to set the time every time he started it up and before it would go into Windows.

So I took a look at it, and while the screen was dead, it was coming out with some POST bleeps. On a hunch, I hooked it up to an external monitor and tried starting it. While the screen was dead, the output to the monitor was OK, and it gave me two codes that I recognised as telling me that the BIOS battery was dead (I'd had to change the battery once before). So I reset the time and date, and it started the normal boot-up. However, while loading Windows, it hung just before completing the load and just locked solid. Even the mouse pointer was dead, and the only way to shut the machine down was by a hard shutdown via the power button.

One thing I did notice while watching it boot up was that the battery monitor was showing 0%. Knowing how battery problems can sometimes do funny things to a computer, I left it plugged in overnight to try and charge the battery before trying again. However, the next time I tried to start the machine, the same thing happened again, and the battery was still showing 0% charge - despite having been left to charge for about 12 hours. Wondering if the main battery was somehow causing an issue with the start-up, I replaced both the BIOS and main batteries with new ones obtained online. This cured the start-up issue, and the machine now boots into Windows OK.

However, that still left the screen problem. Suspecting the inverter (I'd also had to replace that a few years ago), I sourced and fitted a new one, but to no effect. Wondering if the problem was maybe the screen itself, I sourced and fitted a replacement, but again no effect. Just to try all possible combinations of the two, I then removed the new inverter and refitted the old one to try it with the new screen, but still no sign of life from the screen.

So I've now reached the point where I'm stuck and need help. The machine now boots up OK into Windows, and outputs a picture to an external monitor, but there's no sign of life from the screen. Does anyone have any ideas what the problem may be, and what the solution may be? Here's the system specs for anyone who needs them:

T21 2647-8BG, 256MB RAM, 20GB HDD, Windows 2K Pro.

[rkawakami]

Thanks for providing a fairly detailed analysis of what you did and the results you obtained.

From your description, I'm going to suggest three things as the most probable cause: system is defaulting to displaying only on the external monitor, a stuck lid switch or a blown fuse on the motherboard.

For the first item, try powering up the system using the external monitor and when Windows has completely finished loading, press the Fn+F7 key combination. If this magically turns on the LCD screen, then you've found the problem. The Display setting in the BIOS may have been accidentally switched to VGA only. Fn+F7 will switch the active screen to the LCD, the external monitor or both.

If that doesn't work, closely look at the lid switch plunger that's just to the left of the right hinge. There's a hole in the keyboard bezel that has a plastic pin sticking up through it. With the system OFF, jiggle the pin with a tip of a screwdriver but depress it no more than a millimeter or two. Turn the system on and see if that did the trick. If still no-go...

Assuming that you still have an inactive display (and I'm assuming that the replacement panel is still installed AND was guaranteed to be functional), then the next thing to check is the fuse. I believe that fuse F5 on the T21 is the one that protects the inverter board. You can find it just "below" the LCD connector, towards the right side. Here's some scans of the motherboard that were provided to me a few years ago that I'm hosting: http://forum.thinkpads.com/viewtopic.php?t=47660 If you click on the "Top side w/legend" link, then look in the area of B6. You will need a multimeter (ohmmeter) to check the fuse; it's the one with an "N" printed on top. With all power removed, it should read 0 ohms across the fuse. If it's anything other than 0 ohms, then it's blown. I'll have to do a little research on the exact part number but I know it's made by Littelfuse.

If all of this still did not fix the problem, about the only other things that can be wrong is a broken LCD ribbon cable, something else is broken on the motherboard or the replacement panel has a blown backlight.

[JBUK]

If you get nowhere with fixing this then I have a selection of T20s and T23s one of which has a recent brand new LCD.
PM if this is of interest.

[lather]

Assuming that you still have an inactive display (and I'm assuming that the replacement panel is still installed AND was guaranteed to be functional), then the next thing to check is the fuse. I believe that fuse F5 on the T21 is the one that protects the inverter board. You can find it just "below" the LCD connector, towards the right side. Here's some scans of the motherboard that were provided to me a few years ago that I'm hosting: http://forum.thinkpads.com/viewtopic.php?t=47660 If you click on the "Top side w/legend" link, then look in the area of B6. You will need a multimeter (ohmmeter) to check the fuse; it's the one with an "N" printed on top. With all power removed, it should read 0 ohms across the fuse. If it's anything other than 0 ohms, then it's blown. I'll have to do a little research on the exact part number but I know it's made by Littelfuse.

If all of this still did not fix the problem, about the only other things that can be wrong is a broken LCD ribbon cable, something else is broken on the motherboard or the replacement panel has a blown backlight.

Thanks for the ideas. I forgot to mention that I did try cycling it through the various options using Fn+F7 several times, but it didn't do anything.

And I don't think its the backlight, as I've found from experience of the backlight going on my own machine (an R32) a few years back that you can usually still see something on the display if you shine a torch onto it at the right angle. Along with Fn+F7, that was one of the first things I tried, but there was definitely nothing there. As for the ribbon cable, there's no obvious signs of damage, but I guess that doesn't rule out some sort of problem with it.

I'll try the plunger trick to see if that works. As for the bit about checking the fuse, when you say "all power removed", does that include the backup battery as well? And how difficult is replacing the fuse if it is that? Is it a simple pull-out job, or does it have to be de-soldered? I have the gear needed to do that if needed, although it may take a little finding as I've not used it for several years now.

And JBUK, thanks for the offer - I may be in touch if it comes to that.

[Neil]

...how difficult is replacing the fuse if it is that? Is it a simple pull-out job, or does it have to be de-soldered?

For me, it's a very difficult job because the fuses are so tiny. About 1.5mm x 2.5mm, and my eye sight is not so good any longer. One really needs steady hands, 10X magnifying glasses and a good solder station.

That said, the easiest way is to solder the new fuse on top of (piggy back) the old open fuse. Still not easy though.

[rkawakami]

No, you can leave the CMOS (backup) battery connected. I meant only that you should pull the main battery and disconnect the AC adapter when you open the system and check the fuse on the motherboard.

If there's no "ghost" image at all on the LCD when there should be something going there (verified by connecting an external monitor and cycling through the Fn+F7 sequence to enable ONLY the LCD), then that kind of points to a bad ribbon cable or some problem on the motherboard, again assuming that you truly have a functional display in use. The fuse will only affect the backlight and not the video signal (image) being sent to the LCD.