Hello,
I recently bought a T420 that had a broken screen (or so I thought). A broken screen was OK for me since I anyhow was about to do some upgrades, including a 1600x900 panel, but also flashing coreboot onto to it and installing an ivy bridge processor.
So I got all the needed parts, flashed coreboot successfully, put everything together (with the new panel)... and still no picture... Now, I was able to verify that the laptop is working (except for the screen) by using an external monitor + Fn&F7 + live Linux image. Also, while in the live session, if I open some bright sharp pictures I am able to see them on the laptop screen if I point the brightest flashlight I got at the screen. So from what I have read on forums this points to a blown backlight fuse.
I opened up the laptop and found the fuse (verified with multimeter that it is blown), but it is tiny and I am not skilled enough to do the replacement, nor can I source the replacement fuse locally (and having it delivered to where I live would be half the price of a replacement motherboard from ebay). So I am thinking of just jumping it.
But before I do, I would like to know the risks of jumping it. If whatever caused the fuse to blow occurs again, what components can I damage? Basically I am OK with killing the motherboard, since that is useless to me anyhow if I get no picture, but the rest (cpu, ram etc...) I would not like to damage. Also, I got a new LCD cable because the old looked splintered/ripped at the screen connector. Maybe that caused the fuse to blow and therefore it should not happen again now that I got a new cable... maybe? Your thoughts?
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Blown T420 backlight fuse, potential risks if jumping/briding?
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Re: Blown T420 backlight fuse, potential risks if jumping/briding?
Welcome to the Forum.
The most likely blown fuse is either F19 (0.5A, marked F), or F3 (3A, marked P).
Both are described as "fast-acting".
Do NOT bridge a blown fuse, you run the risk of blowing something else!
If you can manage to solder a wire to each end of the fuse on the board, you can then solder a new fuse (of a larger size if you like) between the other ends of the fuse.
Alternative: piggyback-solder the new fuse on top of the old one.
The most likely blown fuse is either F19 (0.5A, marked F), or F3 (3A, marked P).
Both are described as "fast-acting".
Do NOT bridge a blown fuse, you run the risk of blowing something else!
If you can manage to solder a wire to each end of the fuse on the board, you can then solder a new fuse (of a larger size if you like) between the other ends of the fuse.
Alternative: piggyback-solder the new fuse on top of the old one.
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Lenovo: X240, X250, T440p, T480, M900 Tiny.
PS: the old Boardroom website is still available on the Wayback Machine.
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Re: Blown T420 backlight fuse, potential risks if jumping/briding?
On some earlier machines I have soldered a single strand of a 14 gauge stranded wire over the two ends of the fuse. Then a bit of tape to insulate the [censored] fuse assembly.
(It does not like the word Bas tard ized?)
Ron
(It does not like the word Bas tard ized?)
Ron
Last edited by jronald on Sun Feb 18, 2018 7:00 pm, edited 2 times in total.
I see in my son's eyes, each day, the wonders I have squandered fortunes to possess and have sought my entire lifetime to attain. jrr 09/2011
T400's and T500's
T400's and T500's
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Re: Blown T420 backlight fuse, potential risks if jumping/briding?
When I blew the backlight fuse (F7) on my T420 I just bridged it with a wire and it seems fine, for now. :\ Can't sell it like this, though.
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