Troubleshooting a X220 backlight

[thinkpadthai]

Hi all!

I'm new to the ThinkPad world and am really excited to have recently purchased my first X220. It is used but in very good condition. Part of why I'm excited about it is how impressively repairable it is (especially compared to my previous laptop, a MacBook Air). Although I wasn't anticipating needing to do any repairs so soon...

I had opened up the computer, and everything was working fine. Then I re-assembled it, and the backlight will no longer come on. The screen otherwise appears to be operating properly. I opened the machine back up and noticed that moving the LCD display cable would causing artifacts to appear on the screen. I replaced this cable, which fixed this issue, but the backlight sill still not come back on.

From my research, it seems like there are two possible causes to pursue:

1. The backlight might be bad and the screen would need to be replaced.
2. A fuse on the motherboard is blown. I've put off investigating this as I think it means removing the motherboard from the chassis, dealing with thermal paste, etc.

Since I'm still rather new, I'm wondering if there are any other possible causes, such as:

1. Is there a lid sensor that might think the lid is closed when it is open?
2. The keyboard otherwise works fine, but what if the brightness keys aren't working for some reason? Is there another way to adjust the brightness? On a Mac, the lowest brightness level turns the backlight off. Is this also how Thinkpads work?

I'm suspicious that there is something small that would be obvious to me if I wasn't so new since everything was working until I reassembled the laptop the first time.

If anyone has any thoughts or ideas, I would love to hear them. I'm eager to get this machine up and running! Thanks!

[rkawakami]

Welcome to thinkpads.com!

Yes, there is a lid switch sensor. For the X220, I believe it's the same as most of the other modern systems; a magnet and Hall-effect sensor. The (tiny) magnet is generally installed in the base and the sensor located somewhere on the LCD cable. The way it is supposed to work is that when the magnet gets close to the sensor, it will signal the operating system (and BIOS I assume) that the lid is "closed". Since you have replaced the cable, and with it, the original sensor, I'd say that most likely you have a blown fuse, although there is still the possibility that the replacement LCD cable has a missing or defective sensor.

The fuse for the backlight is typically named F2 on the motherboard. I'm sorry to say that I don't know exactly where it is but my best advice is to look around the area where the LCD cable is attached to the motherboard. If you find several "F<number>" fuses, test them all.

The only other way I know of altering the brightness is through the Power Manager settings.

[thinkpadthai]

Thanks for the information! Today I took the motherboard out and checked the fuse F2 and any other fuses near the LCD cable connector. They all seem to be OK.

So I guess my next step is to get another LCD cable and see if that fixes it?

Thanks again!