Electronics > Beginners
Laptop motherboard diagnose
SolderOcelot:
I would love to learn more about diagnosing laptop motherboards. I have an old laptop here to practice with.
Device: Lenovo X220 laptop (motherboard: 48.4kh17.021)
Problem: no power, no boot, no charging led
What do I know? adapter is supplying correct voltage. 20.5V is going IN motherboard but not OUT
Current question: What is the first component to test and how do I find it?
My guess: I should look for a MOSFET because this is the first destination the 20.5V goes to. I don't know if this statement is true. And if it is: how do I identify the first MOSFET to diagnose?
sarahMCML:
Hi,
Looks like fuse F16 just below the input socket in the left photo might be blown?
Regards,
Sarah.
Jwillis:
That fuse F16 looks fine when image is blown up.It has the number 7 on it so I suspect it may be a 7 amp.There should be a silk screen on the board some where that will confirm the actual rating of F16.If in doubt ,just check continuity of any suspected fuses.
The black wires will be 0 volts because they are ground.Both red wires should be 20.5 volts.These are for direct power from the external supply.Not sure what the blue one is for but i suspect it may be the charge wire.
If the battery pack is faulty / removed or other parts are removed then you may not be able to charge or boot the system.For example my lap top will not do anything unless it is attached to the bottom casing.Due to some kind of light switch.Some sort of security thing I suppose.
More information on the make and model of the mother board would be helpful.
SolderOcelot:
--- Quote from: sarahMCML on November 15, 2018, 03:46:45 am ---Looks like fuse F16 just below the input socket in the left photo might be blown?
--- End quote ---
Thanks for your input! I tested it and got .6ohm so it seems fine. Edit: however I do get 0V on this fuse with charger plugged in, measured from one side of fuse to other. Between DC-IN (red) and either sides of the fuse there is 20.5V. That's confusing :palm:
--- Quote from: Jwillis on November 15, 2018, 05:14:44 am ---If the battery pack is faulty / removed or other parts are removed then you may not be able to charge or boot the system.For example my lap top will not do anything unless it is attached to the bottom casing.Due to some kind of light switch.Some sort of security thing I suppose.
--- End quote ---
Very good point, I didn't think of that. That might even explain why the charging LED used to go on but it doesn't anymore now I took the motherboard out. I'm looking for information about this now. If you find something, I'm eager to know :)
edit: I did try to cover the motherboard completely with black t-shirts, still no charging LED / power-on.
It's a Lenovo X220 laptop. Motherboard number: 48.4kh17.021
SolderOcelot:
OMG it works. I plugged in the battery and it's booting. I did notice the fan tried to go on a few times but couldn't. After a few times it kept spinning at high rate and there was boot.
But I'm still left confused and slightly annoyed. I've tried this before and it didnt work.
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