HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

[Zibbo]

This 450 G4 DA0X83MB6H0 REV H motherboard turns itself ON after windows shutdown or after switch long press, even without the hard drive.
I have flashed the bios and changed the RTC coin cell but the problem remains. The motherboard is clean with no signs of moisture or liquid damage.
I am asking for assistance on what I should check.

[mon2]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

With no power, meter in resistance mode.

Check the resistance of the 2 x DCin mosfets.

Source (1-2-3) and drain (5-6-7-8)
Source (1-2-3) and gate (4)
Gate (4) and drain (5-6-7-8)

Often the 2nd mosfet will be defective or leaking.

Confirm the resistance readings. If you read '1' or 'OL' on your meter, then switch to a higher resistance scale to test.

[Zibbo]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

With no power, meter in resistance mode.

Check the resistance of the 2 x DCin mosfets.

Source (1-2-3) and drain (5-6-7-8)
Source (1-2-3) and gate (4)
Gate (4) and drain (5-6-7-8)

Often the 2nd mosfet will be defective or leaking.

Confirm the resistance readings. If you read '1' or 'OL' on your meter, then switch to a higher resistance scale to test.

Thanks for your assistance Mon2, I have checked the 2 Mosfets and they are fine. I even replaced them just to be sure but the problem still remains.

[Zibbo]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

I have noticed that it stays Off when there is no RAM, I don't know if this info helps.

[mon2]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

What are the details of any add-on (slot) devices on this logic board ?

Do you have a wifi module ? Remove it if you do.

When we did our first designs for the PCIe interface for the PC industry, I recall that HP had a bios fault where the wake up line on our PCIe adapter would trigger all kinds of funky faults like, unable to enter the BIOS configuration. The BIOS was clearly at fault but the work around was for us to disconnect this WAKE line. We had shipped very high volumes of our products yet this one new model from HP was acting strange - about 5-7 years after our products were in the field already.

I recall a few years ago on this forum, someone with a similar fault and we fixed it by apply tape onto the gold finger of the PCIe based wifi module. Not saying yours is the same case but it is work to try.

In short, this PCIe interface pin is requesting the logic board to wake up - all the time. If the wifi module is removable - remove it for quick testing.

[mcplslg123]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

Besides wifi module, it can be network controller as well. Next suspect will be dc-dc conversion IC for 3V/5V.

[Zibbo]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

Fixed, thank you guys very much! Upon following mcplslg123's suggestion of checking the network controller, I followed the PCHWAKE# signal and on R645 it was reading 250 Ohms to ground. I then followed it to Connector CN6 and found some corrosion on Pins 8 & 9.
I wouldn't have figured it out on my own. Thanks

[mcplslg123]

Re: HP Probook 450 G4 DA0X83MB6H0 REV H not staying off

Always welcome bro. nice to know it was fixed.