x240 boots with logo, but extremely dark, looks like a black screen.

Discussion in 'Lenovo' started by esmail, Jul 5, 2020.

  1. esmail

    esmail Notebook Consultant

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    I recently replaced the LCD cable on my x240, and then the screen.

    The new LCD cable worked, but my old LCD cracked during the reinstall process, losing the left half of the screen, so I ordered a replacement using the right FRU (or whatever the part acronym Lenovo uses). Now when I try to boot the system, the logo shows up, but it's barely visible on the othewise dark screen. Keyboards/leds etc all work.

    It definitely boots with logo, but extremely dark, looks like a black screen. I.e., the logo isn't bright like usual. Also, I can't tell what happens afterwards, the screen goes blank, but I'm not sure it's going on to Windows or what happens. It's not rebooting on its own though. The system definitely stays on until I power it off (and I can see the screen power off too).

    This is happening with both LCD screens. I also tried the old LCD cable - exactly the same.

    Any suggestions?

    Thanks

    PS: Any suggestions how I can disable the internal battery? Before I would do this with the BIOS, but now I can't get to that screen :-/
     
  2. Mr. Fox

    Mr. Fox BGA Filth-Hating Elitist

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    From what you describe, it sounds like the LCD backlight is not coming on, and if both screens do it I would suspect something with the LCD cable or the contacts at one end not being reliable. Do you still have the old LCD cable you can try to see if it behaves differently? If not, or it is totally unusable due to a broken wire, have you tried manipulating the new LCD cable to see if the LCD backlight flickers or comes on? Be sure to manipulate the connections at each end and the wires running between them. I am assuming your display does not use a separate inverter card. They used to be pretty common, but now they are almost always built into the LCD.

    It is not very likely, but the magnetic switch that turns off the LCD backlight when you close the lid could be stuck in the closed position. Worth investigating if the above leads to nowhere.
     
    Last edited: Jul 5, 2020
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  3. esmail

    esmail Notebook Consultant

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    Yes, I tried the old cable too, same behavior. Is it possible the back light fuse blew?

    Do you have more information on that magnetic switch? I didn't even know there was such a thing.

    Thanks.
     
  4. Mr. Fox

    Mr. Fox BGA Filth-Hating Elitist

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    All laptops have that magnetic switch. They are usually in one of the top corners of the screen or the front edge of the palmrest with a piece of metal on the opposite corresponding part that it closes against. In fact, when the switch is working correctly you can turn the screen off by touching the area with a magnet and thereby identify exactly where it is located.

    It is possible that a short cause the backlight to go out. I suspect they have a fuse soldered on the PCB near the eDP or LVDS connection.
     
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  5. esmail

    esmail Notebook Consultant

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    Thanks .. I was able to find the switch by rolling around a tiny metal screw on the palm rest (learn something new every day) .. unfortunately, in order to look at the fuse I'd have to totally remove the motherboard as it is on the underside of the LCD connector, took a number of google searches to establish that. I know the part and what to look for I think.

    That may take some time, plus it's not quite clear to me that I could do anything about the fuse on the motherboard :-/
     
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  6. Mr. Fox

    Mr. Fox BGA Filth-Hating Elitist

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    If you can find it you can easily replace it with a fine-tipped electronics soldering iron or hot air soldering station fairly easy. It sounds intimidating, but I have done things like this numerous times... born out of necessity. You can probably purchase a new fuse exactly like the one that is on it from Mouser or Digi-Key. If the alternative is replacing the motherboard, you've got nothing to lose and everything to gain. It also produces a great sense of personal accomplishment when you replace a tiny part that costs like one-tenth or one-twentieth of the postage charges to mail it to you and saves you literally hundreds of dollars.

    Once you find it you could try momentarily bridging it to see if the backlight comes on, but if there is a dead short somewhere else that could result in harm. But, it would also immediately blow the fuse. That is probably not the case though. If I were going to take a guess, possibly a severe ESD situation would be the most likely cause.
     
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  7. esmail

    esmail Notebook Consultant

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    Ok, thanks. I'm no expert on soldering, but first I'll see if I can locate and examine the fuse. Then I may try bridging it to see if that really is the cause and take it form there (and that would be an area I'm definitely not an expert in). Got nothing to loose at this point though.

    I was planning to upgrade to a new Lenovo (T490 possibly), but not right away .. sigh.

    Thanks.
     
  8. Mr. Fox

    Mr. Fox BGA Filth-Hating Elitist

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    What country or state to you live in? Even if you're going to upgrade it would be great to fix it if you can do it cheaply. You definitely have nothing to lose and it's not difficult. I am not a soldering expert either. But, I hate spending money replacing expensive parts when something that costs less than a dollar needs to be replaced. If you have a knack for electronics (or even if you do not) you could actually make good fun money in your spare time fixing things ordinary people would normally throw away.
     
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  9. esmail

    esmail Notebook Consultant

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    I'm near Chicago, I'm definitely not going to throw this out, but keep it to see if I can revive it for sure - I also don't like unnecessary waste if I can help it. I've had this system in almost daily use for over 6+ years, and the tower I built for 8+ years. Usually won't upgrade unless I need it. I do need a working laptop though, and I had been thinking of upgrading, so this may be the time. If I can get this system to work again, I'll have a second backup system.

    Not a super-expert in electronics, so doubtful I could to much for others, but I'll give it a try for myself on this. Thanks for the encouragement. I may ping you for some additional tips when the time comes (hope you won't mind).
     
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  10. Mr. Fox

    Mr. Fox BGA Filth-Hating Elitist

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    No, I don't mind at all.

    I am near Phoenix. If not for the COVID-19 lock-down bullcrap, I would still be traveling to Joliet a week every month and I'd offer to help you after work one evening. But, sure... feel free to send me a PM if you have any questions and I will try to help.
     
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