Need help troubleshooting a faulty motherboard (Lenovo U41-70)

[ghostiee]

Hi,

I've been a technican for many years but I can only troubleshoot to the major parts, and I know nuts about component-level such as capacitors, resistors, ic chips, soldering etc.

My own laptop's motherboard failed - no power no response at all. AC adaper is working fine.

I just bought a multimeter and checked the piece of AC charger port cable that's connected to the motherboard.



After connecting the AC adapter and turning on the power, I measured 20V on the following combinations:

PIN 1 & 4
PIN 1 & 5
PIN 2 & 4
PIN 2 & 5

I assume PIN 1 and 2 are + while PIN 4 and 5 are ground. This cable is OK.



I connect the cable to the motherboard and measure the connectors to the motherboard. As pointed out by the red and orange arrows, I am NOT ABLE to get 20V. When measuring PIN 1 or PIN 2 with ground, I am only able get a reading of 0.x to 1.0 V.

What is the issue?

Additionally, I notice one IC that seems to have "burst". "7401" and "GA5T1A" are printed on the chip but I tried many search engines and parts/components database, I just can't find anything relevant.



This burst chip is very small and very near to the power connector on the motherboard. If you refer to the second photo, you can find reference of the burst chip relative to the power collector by looking at the location of "PJ511K" chip on both photos.

In the second photo, you can also see how small is the burst chip relative to my thumb.

Any help will be appreciated!!!!

[Uranium-235]

Re: Need help troubleshooting a faulty motherboard (Lenovo U41-70)

you posted this on like 3 different forums. It's probably a MOS chip but it looks like just flux, not 'burst', still could be bad though.

sometimes I miss my admin power to move this to the laptop forum

[SMDFlea]

Re: Need help troubleshooting a faulty motherboard (Lenovo U41-70)

you posted this on like 3 different forums. It's probably a MOS chip but it looks like just flux, not 'burst', still could be bad though.

sometimes I miss my admin power to move this to the laptop forum

Agreed,this should be in the laptop forum.

What is the part number on the mobo ,it may start with LA- .The white part at the end of your finger on the 2nd picture is a fuse. Desolder that to start with and test it . The "burst" chip is a Alpha Omega AO7401 https://cdn.badcaps-static.com/pdfs/...05b74370b3.pdf

[stj]

Re: Need help troubleshooting a faulty motherboard (Lenovo U41-70)

what's the resistance between the tab and pins on that part?

[Krisdf]

Re: Need help troubleshooting a faulty motherboard (Lenovo U41-70)

Hi!
Sorry to be posting here since it's in the wrong category, but I have the exact same laptop with the same symptoms described by OP.
Looking at the MOS chips in question I can confirm mine also looks flux/bust
When the laptop is plugged to A/C a "clicking" sound begins to emerge becoming louder the longer its plugged in (though its still faint even when loudest)
The chip depicted by OP also becomes very hot! Like to hot to touch. Of course this may be by design though....

Op have you gotten closer to a resolution?