Stuck at IBM boot screen, backlight bad but LCD works

[tonfagun]

Hey.

I've been searching the forum for a while and didn't find my exact problem in any older posts, so I hope it's okay that I'm posting about my problem:

T43, 1875DAU. A few weeks ago, the backlight of my Thinkpad stopped working. After reading a bit about it, I figured that it's most likely the inverter, since I could still faintly see the LCD image given the right angle and light in the room. Note that at this time, the display was the only problem, the computer booted just fine.

I bought an inverter, but it did not have an identical part number as the one I replaced: the part I bought is FRU 39T0360, the original is FRU 27K9974. I figured it would be okay since both are inverters for T43, 15 inch screen models, the only difference seemed to be that one is for a lead free LCD and the other one is not, IIRC.

After putting in the new inverter, the backlight turned on again, but then the computer got stuck at the IBM startup screen (the screen saying "To interrupt normal startup, press the blue Access IBM Button"). I'm not sure if this new problem has been caused by me changing the inverter, since in the meantime I had also opened the computer and removed some dust from the inside, i.e. it's possible I damaged something (the board?) while doing so.

So the current state is as follows: when I turn on the computer now, the LCD turns on and the backlight works at first, the CD drive spins, but then the system gets stuck on the IBM startup screen. After about a minute or so, the backlight turns off (as if the inverter is still faulty), but the LCD image is still faintly visible.

Some more ideas I had/things I tried:

* I cannot enter the BIOS, the only keys that show a reaction are the power button and the LCD brightness keys.

* I tried starting with a Linux boot disk, but the computer never goes beyond the IBM screen.

* After searching the forum now, I wondered if I maybe suffer from the 'lose GPU' problem, but in that case, I shouldn't be able to still see a faint image (which I do), right?


Any ideas how I can find out what's wrong? Could this be possible the symptoms of a depleted CMOS battery?

[poshgeordie]

Hi Tonfagun and welcome to the forum.

Regarding not accessing the BIOS etc, I've seen this problem occasionally and it's normally an unsoldered Southbridge (SB) chip.

To test this (this doesn't always work), remove the keyboard and palmrest and remove the wi-fi card. Temporarily reconnect the keyboard and before starting up the laptop press down on the the SB chip - the big square chip under the wi-fi card.

Whilst pressing down on the chip start up the laptop - can you now access the BIOS?

Regarding the backlight turning off after a minute or so, I'm not sure why this is happening but could be connected with the SB issue.

Check out either my sig or the right hand blue banner at the top of the page - we do chip resoldering in UK and Europe and I'd be happy to look at your laptop including checking out the inverter issue.

[MnR]

Hi,

Did you try an external monitor with the LCD disconnected? Also after looking up the model number you gave it shows that that Laptop came with the 15" XGA screen not the SXGA.

Are you sure you have both connections secure? if one or both are loose that could be your problem.

MnR

[Harryc]

For a 15" XGA T43 LCD you need inverter FRU# 27K9974 or 39T0359. You have an SXGA+ inverter there...won't work.

[tonfagun]

Thanks a lot for the answers so far. But just one follow-up question regarding the wrong inverter model I am using: that still doesn't explain the notebook not booting anymore, right? A defect or wrong converter won't make the system get stuck on the IBM screen, like mine does.

(I will try poshgeordie's suggestion later today, pressing the SB chip, to see if that helps to go through normal startup again)

[Harryc]

A defect or wrong converter won't make the system get stuck on the IBM screen, like mine does.

It's difficult to say...I've never tried the 'wrong' inverter. I'd assume the backlight either would not go on, the inverter itself would short/burn up, or might go on then off. It might also damage the CCFL (backlight) and/or blow a fuse on the systemboard.

[tonfagun]

<long list of bad things that could potentially happen when you use a wrong inverter>

Sounds like I made a very smart choice then by plugging in that almost-right inverter....

[tonfagun]

update: I replaced the new (wrong) inverter with the old (malfunctioning) one. Unsurprisingly, the backlight still doesn't work, but it seems the system at least starts up normal again, i.e. doesn't get stuck at the IBM screen. It looks like the non-fitting inverter caused the problem, but I'm not sure. I ordered the correct inverter model now, I'll write again when I've received the part and put it into the notebook.

[tonfagun]

Update #2: turns out poshgeordie was right. The 'stuck on boot screen' issue re-appeared, and was at least temporarily solved by pressing on the SB chip. Not sure if it's worth repairing this.

[poshgeordie]

@Tonfagun - PM sent.