Sony Vaio SVS MBX-261 board failure

[delpiero3]

Hi everyone, newcomer in this forum, i watched tons of video from Sorin, i like the way i calmly explain things, i did quite some console repair, i am not that bad at micro-soldering, but troubleshooting where the issue is, is definitely where i still have progress to make. Usually i was able to fix the console because the failure was obvious, or because i was able to find someone with similar measures on the board and was pinpointing what to replace that way.
Nevertheless, let's say, i don't come as a total beginner.
I have this old laptop, which suit perfectly my needs, with the following specifications :
- Sony SVS15
- Intel Core I7-3632QM
- Nvidia GT640M
- 4GB of RAM soldered on the board
- Motherboard MBX-261

The laptop was working fine, no issue, but i noticed that the fan was spinning more than usual, so i powered it off, and started to disassemble it to replace the thermal paste. It was never done, so i thought it is time for it, the laptop is something like 11-12 years old maybe.
After i did replace the thermal paste and reassemble everything, no power. I press the button, but nothing happens. However, the battery is charging and i could see the orange light.
So i started with the usual :
- remove all accessories such as SSD, Wifi board, additional RAM module, etc ...
- clear CMOS by removing the battery

Still nothing.
I disassembled again removing additional stuff such as keyboard, etc..
Still nothing
I started to measure the voltages, i have 19V not shorted, 3.3v is present, 5V is present and 3.3 present at the power button as expected, but still not able to start the board.

I placed in the picture what i have. It is not obvious for me what happened, i triple check my work when putting the board back, and i did not made any mistake.
I only found a strange issue, with what looks to be a power regulator, the corner of it was broken, not sure if it has an influence but i put a picture.
I also placed in the picture the resistance to ground i have for each coil.
If someone have an idea where should i continue to look, because i am a bit lost.
Thanks.

[rogfanther]

Is the power button on a secondary board, connected through a flat cable ? Have you checked if this flat cable is not damaged ?

[delpiero3]

Thanks for the help.
Yes i checked, i get the 3.3V on the power button itself, pressing it cause the voltage to go to 0V and then back to 3.3V. On the other end, i checked all the fuses of the board, all looks good, when no battery is present, the board eats 4mA on the DC-in and no difference if i press the button, when the battery is in, it starts to a steady 230mA and then jump to 500mA, again no difference if i press the power button on the current.

[mon2]

Can you link a schematic if available? Do not post it here but inside of the dedicated schematic forum only.

There is no current draw from the power adapter side of the power path. Which charger IC is onboard? Test the DCin mosfets in the power adapter path to the main power rail for this board.

The VT370F IC that has been slightly wounded since this is a BGA device.

Available (of course) on Aliexpress:

https://www.aliexpress.com/w/wholesa...etail.search.0

[delpiero3]

I unfortunately have no schematic for this board, i have been looking all around the web with no success.
The charger IC is the BQ24725. Both mosfets looks good, i see 19V coming through and i don't see an issue with it.
However, i am wondering if i don't have an issue with the BQ chip, because on the screenshots, where you see 1.2V at the coil next to it, on a working board i have 2.4V. And this voltage directly comes from BQ. I ordered few of them tro try it out, i don't want to mess with my working board. I also ordered few VT370F in case of, but i am really wondering if this little wound can cause an issue on it ?

[delpiero3]

When i plug the battery in, i have pretty much the same value on both BQ chips, so i think i am good here probably.

[delpiero3]

I checked the bios chip, no power on leg 8, and i compared with the good board to make sure i wasn't mistaking. I traced where the 3.3 was coming from, and guess what, from this VT370F power regulator. I have 3.3V on top right corner resistance on the good board, not on the bad one.
Once i receive new one, i will exchange and let you know.

[delpiero3]

Mmmh, i think i was speaking too fast. I am under the impression that the top right corner of this VT370F is the VCC, and therefore, i should get 3.3V there compared to the working board and i have nothing. So back to square 1, i don't know where the 3.3V of the bios leg should come from, i have no way to trace the track. How do you proceed in such condition ?