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]

Looks like fuse F16 just below the input socket in the left photo might be blown?

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 

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.

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.

[KILLorBE]

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 

When you measure across a component you measure its voltage drop, for a fuse that's about 0V, so there's nothing wrong with that.

I don't know that much about laptops or electronics, but the following tips may come in handy when troubleshooting a laptop:
Hook up an external monitor or use a flashlight to see if the inverter is dead (Pretty common failure, with older laptops the CCFL's could also be dead) -> point the flashlight on the monitor at an angle and startup the laptop (point the flashlight where there's most likely some text or a logo), if you can see something happening you know it's most likely the inverter or possibly the CCFL's.
It may take a little practice when you don't know what to look for, but this may give you an idea:

Tap near the touch-pad or the entire front edge, usually there's a reed switch which might be stuck, thus it will tell your laptop the lid is closed and it may prevent your laptop from booting or the backlight from turning on.

The power jack is a pretty common failure as well, but there are too many different laptops to describe all common problems (For example: a common problem for HP DV series laptops is that they tend to have the graphics card fail...), so whenever you have a laptop with a problem, first thing to do is google if it may have common problems.

[KILLorBE]

I forgot to mention a couple of things:

Check out some videos on YouTube, I recommend watching some videos by iPad Rehab and Louis Rossmann, while they are mostly Apple related, you may learn a thing or two on how to troubleshoot.

Also, Louis Rossmann used to have some links in his video description, like (It's truly a coincidence that I picked this one), scroll down to were it says: LEARN HOW TO DO THIS

Maybe it's helpful (Haven't looked myself (yet)).

[MyHeadHz]

The symptoms you described are very common.  It doesn't appear to have any liquid damage, which is definitely a plus.

By far the most common root cause in this situation is a failing input connector on the laptop itself.  Sometimes these are soldered onto the mobo, and sometimes they are on their own board.  Either way, it is important to rule this out as a possible cause before anything else due to the risk of fire.

To check it, simply plug it in and watch the charging LED.  Then move the plug around while it is plugged in and see if the light blinks.  It will probably blink as it gains and loses connection.  It can be corrected if caught early (likely your case) by re-soldering connections or replacing a connector, but it depends on a few things.  Pictures of the input connector on the mobo would help.

It could be other things, but that's is the most likely based on what you've shared so far.

[magic]

OP fixed this laptop half year ago

[SolderOcelot]

Actually it's dead again. I really want to use this motherboard to learn board repair but I just don't know where to start.

Should I just try without schematics?
What component should I start checking first?
Which side of the board do I start with?

[xmetal]

Do a search on google for Lenovo X220 schematic and you should find it. I just tried that myself and I did find it.