Asus Probook P5440UF-XB74 power issue

[GLISIT]

Hi all,

TL;DR - this laptop is driving me nuts with the oddball power-related behaviors. Appreciate any insight you can provide!


I'm experiencing a power issue on an Asus Probook P5440UF-XB74. Although I've worked with electronics and computers for decades, this is my first attempt at getting into motherboard-level component troubleshooting. Any help the community can provide is greatly appreciated!

A few weeks ago I was using the laptop (on battery power) for a Zoom meeting. The battery was running very low (long meeting) but I wasn't worried about it actually running out before the meeting ended. A couple of minutes later, the laptop just turned off. I grabbed the power brick and plugged it in but it just refused to turn on. Later I tried with my other power bricks and nothing.


I searched for the schematics for the board but haven't been able to find anything. I did some cursory checks, both visually and with the voltmeter, and also ran some troubleshooting tests. Here's a list of what I've done and found so far:

• I have 3 power bricks for this laptop, all original to the laptop (two are travel adapters, one is for the Asus SimPro Dock 2 docking station). None of them worked to power on the laptop.
• Checked voltage of each of the power bricks with DMM and they're as expected.
• Removed the SSD, extra memory chip and WiFi card but still wouldn't power on. Reinstalled them.
• Thinking there might be a problem with the power connector, I used the USB-C dock to connect to the laptop. It still wouldn't power on, but I could measure voltage on the board at 19.3v +/- 0.1v
• When I tried again with the power bricks, there was no voltage on the board. Further testing revealed that the power brick protection circuit was kicking in when connected to the laptop, which leads me to believe there is a short somewhere on the board.
• Removed the battery and connected the USB dock, measured power to the board trying to guess the voltage path toward the battery, noticed that voltages where fluctuating between 5v-19v, cycling back and forth. Is this related to the battery charging circuit?
• Noticed for the first time the power button light was lit, and showing what looked like an error code. I couldn't find any online sources specific to laptops error codes.
• Pressed the power button and the laptop turned on. It seemed slow to boot, but once on the desktop I confirmed it was definitely much slower, taking minutes to even launch task manager.
• Although it was powered up running on USB and with no battery, on screen, the laptop kept switching between Power and Battery icons, as if power was turning off and it tried to switch to battery. Seems to reflect the board power fluctuating in a similar manner.
• Removed the BIOS battery, let it sit for about an hour. Tried to power up the laptop but it would not do anything.
• Put the BIOS battery back in, can't power via Dock but can power via brick... this only added to my confusion. Laptop still slow, taking 1 minute to respond to minimizing a window. Shut it down.
• About 30 minutes later, attempted to power back up with power brick, no go, but it did power up via USB dock. Ugh!
• I shut it down and booted into an old USB flashdrive with Dell diagnostic tools. Mostly wanted to see if it was as slow as with Windows, but letting it run a memory diagnostic first. I will report back once the memory test is done.

Can anyone help me make sense of all this?

Thanks!

Edit: Forgot to mention that I found two electromagnetic coils with some kind of seepage. All I can think of is the insulation melted and seeped out? Image attached.
Edit: Also, adding two short videos

[FriedFred]

"fluctuating between 5v-19v, cycling back and forth. Is this related to the battery charging circuit?"
This behaviour looks like it's coming from the USB PD controller.
This controller negotiates the voltage which can be applied from the USB power supply.
It starts with 5 Volt for communication and after some seconds, shall switch to a higher voltage.
But this higher voltage should be stable, of course, If this higher voltage gets down immediately, this can have 2 reasons:
A) The battery is fully loaded. B) There is a short-circuit, which forces the PD-controller to switch-off.

"Noticed for the first time the power button light was lit, and showing what looked like an error code. I couldn't find any online sources specific to laptops error codes."
But this is a great sign! Because it shows that the BIOS and the EC-controller is still alive and also the relevant power rails.


"Seems to reflect the board power fluctuating in a similar manner."
This can happen if your PD/Charge controller switches forth and back between the two power sources. For example 19 Volt from external power supply and 16 Volt from internal battery.

Or another reason:This can happen if your external power supply is not able to deliver the requested and necessary current.
For example, if you need 5 Ampere, but your power supply can deliver 3 Ampere only, then the PD/Charge controller can try to switch to battery.
It can happen also if your battery can not deliver the requested current. For example if the battery is too old.

There might be also some kind of dirt or anything else, which confuse some sensitive signals.
Also solder paste and flux must be cleaned-up prior to start the board.
A "no-clean" flux does not mean that it can be remaining on the whole surface and small components.
It can be remaining on solder pads only.

Sometimes a very careful cleaning of the whole board solves problems. Especially, if maybe somebody else has been working on this board prior your attempts.

Hope that some thoughts are useful.

[GLISIT]

Hi FriedFred , thanks for the detailed response!

Some comments on what you said:

"But this higher voltage should be stable, of course, If this higher voltage gets down immediately, this can have 2 reasons:
A) The battery is fully loaded. B) There is a short-circuit, which forces the PD-controller to switch-off."

If I connect the battery, the laptop will not start, so at this point the battery is not involved, hence why I also think it's a short-circuit somewhere.

"Or another reason:This can happen if your external power supply is not able to deliver the requested and necessary current."

I have tested with three power adapters, as I have two original ASUS travel adapters and one original docking station power brick.

"Sometimes a very careful cleaning of the whole board solves problems. Especially, if maybe somebody else has been working on this board prior your attempts."

The laptop has not been worked on prior to me, as I am the original owner. It was working fine up until a couple of weeks ago. Not ruling out that a cleaning wouldn't help, but the only suspicious items I've found are two coils which seem to have leaked some white material.

Hopefully I will be able to get back to the laptop soon, check on any cleaning and continue chasing the suspected short.

Thanks again!