Asus X551CAP fried motherboard searching for replacement part

[grun]

So i disassembled the laptop just to find out why the laptop does not turn on i suspected broken Adapter connector that's easy to fix but it did not turn out to be that so i tried to find some schematic or something to see what kind of replacement i can use and the research lead me here i took some images so you can see the exact location.

[piernov]

Re: Asus X551CAP fried motherboard searching for replacement part

Attached is boardview and schematics for similar boards.
Burnt component (power MOSFET) is labeled PQ8807 on the boardview and PQ8802 in the schematics. Should be the same as the one just above it in your picture (on which you can still read the markings to buy replacements).
You should probably replace both MOSFET and the current sense resistor below (doesn't look nice, marked R010 on your picture, labeled PR8806 in the boardview/schematics, should measure 0.01 ohm).
Also check for a short to ground on the AC_BAT_SYS line, maybe another component is probably dead. Charger IC might be dead too.

[BlueMidnight]

Re: Asus X551CAP fried motherboard searching for replacement part

I agree, you need to check for shorts because that might be why it burned up in the first place. Check for liquid spill damage too.

Also, I recommend removing the bad component before ordering a new one. That way you know what you're in for. There's a good chance the whole pad is destroyed.

Use a brush and some IPA to clean it and get a better look. Desoldering might not work if it is too damaged. Cutting/scrapping may be necessary. And you absolutely must remove every bit of charred area. That stuff is conductive and can cause a short.

If there is no pad left, you can use a small piece of FR4 board and some jumper wires instead. But mount it in the same spot. The MOSFET is supposed to be physically close to those little capacitors. You can also use filler and copper foil to make a new pad, but that's more expensive.

[grun]

Re: Asus X551CAP fried motherboard searching for replacement part

First of all thanks for schematic and fz file i still have not figured out how to open it, . So what happened friend decided that we do what we can make it work or brake it even more, so what we did we removed the burnt power MOSFET and we where unable to find compatible or same to replace, so what we did we removed another MOSFET from the same board that we thought is for battery charging arrow in image is pointing to the removed one i had no time to make few images sorry so i used one from the internet. And voila notebook is working for 2 days so far battery charges !!! checked usb port they work also so i am in a little doubt but it works and he still uses it after 2 days no overheating or anything.

[piernov]

Re: Asus X551CAP fried motherboard searching for replacement part

For the .fz file you can use PCBRepairTool to open it or OpenBoardView ( https://github.com/inflex/OpenBoardView , given you have the decryption key, you may ask on the IRC channel).

Nice to hear it works again. You didn't put back the MOSFET you removed? Without it the laptop may not work without the AC adapter.

[grun]

Re: Asus X551CAP fried motherboard searching for replacement part

No i did not put it back, just the board has 1 less MOSFET now. still trying to figure out what did i actually removed(meaning i though it is for battery charge but it is not cause battery charges just fine). I also suspect HDMI cable will not work now but had no cable to test it. All in all it works i will just try to open schematic to let you know exactly what i removed it might help to someone with similar problem with that board. And if you don't needed why not remove it :P in order to fix it. eh

[piernov]

Re: Asus X551CAP fried motherboard searching for replacement part

I think it is for connecting the main power rail to the battery, ie. when the system is working off of AC power this MOSFET is open, and when it's working on battery power this MOSFET is closed. If you're not using the battery it's not an issue, but if you plan to use the computer on battery power you should find a replacement.