[solved] X401 motherboard - No power

[Vicolaships]

Hello,

My Asus laptop does not power up anymore. It does not work on battery nor on the charger.
None of the LED lit up and the CPU fan does not start.
I have tried removing the RAM to boot but it does not help.
The laptop has not suffered from any water damage / shock.

- Laptop model: F301-RX073V (similar to X301A)
- Motherboard: X401A Rev 2.0
- Charger: 19V 3.42A AC to DC

I have tear down the laptop to extract the motherboard and began testing basic things:
- The power supply does deliver 19V as expected.
- I can measure 19V across the connector pins on the motherboard.
- I have tested the power button, it's resistance drops to zero when pressed.
- The capacitors on the motherboard look OK: none on them is stained or deformed.

There are inductors, MOSFETS and ICs near the power connector but I am not sure what to check first and how to.

Components I have identified:
- 2D5 27 25V electrolytic capacitors
- 2D3 560 2.5V electrolytic capacitors
- A5 GNA 802807 (MOSFET)
- 4955N RWS09 (MOSFET)
- R360 1215F inductors
- Richtek RT8885A IC: Dual Output 3-Phase + 2-Phase PWM Controller (https://www.richtek.com/Products/Vcore/Vcore%20Controller/RT8885A?sc_lang=en)

When the motherboard is connected to the power supply I measure 4V across the 25V capacitors (does not feel right) and 0V across the 2.5V capacitors

Pictures of the motherboard:








This connector is where the power supply comes from:

This is where I measure 19V. The wires go to another board on which there is the barrel jack.

If there are particular chips you want pictures of or detailed description please ask!

I have:
- A logic analyzer (no analog input)
- A multi-meter (no capacitance mode)
- Iron / tin / flux
- Patience

What would you check next to narrow down the problem?

Bye!

[Rasz]

anything happen at all when pressing power?
any voltage on power button?

[Vicolaships]

Nothing happens: CPU fan does not start, power indicator LED does not light up.

When the power supply is plugged in the voltage on the button changes in a ~ 1Hz cycle (with no intervention): it goes from 0V to ~800 mV.
I have noticed that at the same time I can hear a (very small) click coming from the motherboard, just before the voltage drops to zero.

It is hard to tell where it comes from exactly but I'm pretty sure it is one of the components on the picture I sent (near the power supply connector).

Maybe an electric arc ? What component could be the cause?
I'm going to read about MOSFET today and if it is possible to test them without removing them an with a multi-meter.

Thanks for your input

[Vicolaships]

I followed the sound (listening to the motherboard ) and it seems to come from this chip (It's hard to be sure):



It does not look damaged and I can't see cracks on QFN pads

This chip is a main power supply controller: https://www.richtek.com/assets/product_file/RT8206L=RT8206M/DS8206LM-07.pdf
Does the laptop use this chip when powered from the external power supply?

It's a very small package and I did not manage to check the voltages on the chip yet

[Rasz]

clicking is a dead giveaway of shorted rail
sadly it isnt the super easy 3 minute job main power entry mosfets
unplug everything, measure resistance to ground on every coil/big capacitor on the board, start with RT8206 3.3v/5v rails

[aqibi2000]

Wow, there’s a lot more to repairing laptops than just stabbing at an IC you can find the data sheet for.

Find the schematic diagram (using google most definitely you will find it online for free)
Following the power sequence shown in the pdf you will be able to I identify which power rail is shorted and in which power state S5,S3... S0

In the S5 state (without pressing the power button) verify they RTC is 32.786khz and the 3.3 and 5V always present voltages are at the right level.
You can look into the BIOS being an issue the EC (SIO/KBC) etc.

So all you can hope to do it measure across random ceramic capacitors to see if there is a short circuit without tracing


Ps don’t start reflowing the cpu or pch

[pharaon]

1-unplug the battery.
2-unplug the Bios battery and bridge the both sides of the "bios battery place" to reset the Bios and try if it work

if not working then

3- make sure the charger plug have power and connect it to the laptop
4-check the charger port on the motherboard have a voltage.
5-check 19v present on the board by any mosfet
6-check 3.3v present on the power button
7-check the current resistor after the current entrance from the charger " first mosfet > second mosfet > then the current resistor"
8- also remove the screen socket from the motherboard and check if the mother and the processor fan will start

if you can't find the bad component here is what to do>> so focus
1-any capacitor is like a small battery is it + positive and - negative  side
2- so you find which is the - negative side of a big capacitor on the board it will always be connected tot he ground.
3- then with buck converter or and "dump power supply" which is power supply without safety circuit so the power current wont shut down at a shorted board
4- make it to 19 volt and 3 amp current and connect that to any ground point on the board and to the positive side of the capacitor..
5- with the back of your finger find any component on the mother board that is getting really hot and that will be the shorted one to be replaced

[JKKDev]

1-unplug the battery.
2-unplug the Bios battery and bridge the both sides of the "bios battery place" to reset the Bios and try if it work

if not working then

3- make sure the charger plug have power and connect it to the laptop
4-check the charger port on the motherboard have a voltage.
5-check 19v present on the board by any mosfet
6-check 3.3v present on the power button
7-check the current resistor after the current entrance from the charger " first mosfet > second mosfet > then the current resistor"
8- also remove the screen socket from the motherboard and check if the mother and the processor fan will start

if you can't find the bad component here is what to do>> so focus
1-any capacitor is like a small battery is it + positive and - negative  side
2- so you find which is the - negative side of a big capacitor on the board it will always be connected tot he ground.
3- then with buck converter or and "dump power supply" which is power supply without safety circuit so the power current wont shut down at a shorted board
4- make it to 19 volt and 3 amp current and connect that to any ground point on the board and to the positive side of the capacitor..
5- with the back of your finger find any component on the mother board that is getting really hot and that will be the shorted one to be replaced

Everything but the last paragraph is fine. The last one I wouldn't advise executing without a schematic or the knowledge of which voltage should be on what capacitor. Eg. If you put 19V on a CPU power supply rail (1.2V, 1.8V,...) you just made yourself a big ol' paperweight.

[janoc]

Everything but the last paragraph is fine. The last one I wouldn't advise executing without a schematic or the knowledge of which voltage should be on what capacitor. Eg. If you put 19V on a CPU power supply rail (1.2V, 1.8V,...) you just made yourself a big ol' paperweight.

Also the rails certainly have to be powered up in a certain order, so even bringing the correct voltage to the rail could still fry things if the other rails are unpowered or powered up in the wrong sequence.

A really dangerous advice without having the schematic on hand and understanding the power requirements of the circuitry!

[Vicolaships]

Sorry for the late reply!

I have continued investigating the issue:

- I have found a board-view file and a (crappy) "repair guide".
- The BIOS battery is at 3V so it's good. I un plugged it, shorted the 2 pins and put it back: no change.
- The charger outputs 19 V as specified.
- I can measure 19V across the connector pins on the board.
- Voltage on the power button is 0V / 0.3V, it changes a little bit: it's never near 3V. The push button is not received the normal voltage.
- I get zero resistance between all electrolytic caps negative side and ground.
- The RT8206 does not have correct 3V / 5V lines, all of them are close to 0 / 0.3V (it changes a bit too)

Something before the RT8206 is broken  because its not powered properly.

If have found the first two MOSFET that are just after the power supply connector; something is wrong there.
They are P0903BEA N channel enhancement MOSFETs

The voltages are not correct on the first MOSFET except for the input (19V). I'll investigate this afternoon and report my results here!

Thanks for all the messages so far, you are of great help/support 

[Rasz]

upload boardview if you want specific help
you said it was cycling = not the first mosfet after the connector, at least the standby supply must be trying to start and short is after Edit: unless its the laptop charger itself cutting power

[Vicolaships]

I've got good progress!

If I measure the voltage at the gate of the first MOSFET I read 0 volts then after a second I read 23.5 V.
After that the clicking noise stops, I read 3V on the power push button and I can start/stop the laptop normally.

It also sometimes happens that the laptop starts without pressing the power button / on its own (this already happened to me when it was still working, but not often).

Thanks to this "trick" I managed to fully recharge the laptop battery. The laptop works fine on battery (no A/C adapter connected) without any tricks.



The capacitor on the grid pin is a 2200PF/50V (0402) X7R 10% (part reference: YAGEO/CC0402KRX7R9BB222)
I tried to test the capacitor with my multimeter in resistance mode (2000k Ohm), I can see the resistance changing value (also works when reversing +/-) so I think the capacitor is ok.

Could it be a broken junction? I measure continuity between the capacitor and the grid pin of the MOSFET.

There is also something else worth noting; there is a via near the MOSFET but I don't see it on the board view

Boardview and repair guide are available here:
https://easyupload.io/1gmul4

The MOSFET/capacitor are on the bottom view, bottom left corner:


What are your suggestions ? Cheers 

[timenutgoblin]

I thought this might help the O.P.

[Vicolaships]

Very interesting thanks, my problem is very similar but I cannot find a short on one of the capacitors so I suspect the MOSFET itself.

I have ordered a hot air station, 5 of the MOSFETs and I'll get back to you after I have replaced the MOSFET!
If it still does not work I'll monitor the voltages and try to remove some of capacitors.

It will be more than a month until I get the components, I'll have to be patient 

Bye

[Vicolaships]

I have received the chips, I replaced the MOSFET and everything works as before! Thanks for the help