Probook 450 G6 Blink 5 times - No boot - NEED HELP!

[BachPhi]

• Issue:
  Notebook blinks 5 times on power-up and does not boot.
  
  Actions Taken:
  • Tried multiple reset key combinations: V, B, Win, Win+V, Win+B.
  • Removed and inspected all components on the mainboard (Part No. DA0X8JMB8E0).
  • Replaced the RTC battery (CR2016W).
  • Swapped in a different RAM module.
  • Checked the BIOS chip (Winbond 25Q128JVSQ):
    • Measured Vcc = 3V
    • /CS signal stays high after power-on (no activity).

[mon2]

Review the power diagram on page #2 of the schematics.

What is the history of this unit?

Do you have a stable adapter voltage on the main power rail?

Do you have a stable 5v on the USB VBUS rails? Often, the root cause is a defective USB load switch because these days, you can stuff the USB connector with a fan or coffee maker, etc.

Suggest to remove all power -> meter in resistance mode -> measure the resistance to ground on each and every inductor to hunt for defective power rails (starting with the VBUS 5v).

[BachPhi]

Thanks for your response. Full disclosure: I’m new to motherboard-level repair and still learning as I go. I’ve downloaded OpenBoardView along with the schematic for this board. The laptop was working fine previously, but after sitting unused for a while it now fails to boot—the Caps Lock/Num Lock LEDs flash when I press the power button. No USB devices are connected.

I’ve already tried booting with the M.2, SSD, SD card, touchpad, and other peripherals removed, but the issue remains. I’ve been studying the power rail diagram on Page 2 of the schematic. Could you explain, in general terms, how to trace a rail from the schematic (Page 2) to its actual physical location on the motherboard?

[mon2]

Confirm your replaced coin cell battery is ~3v - this is very important.

https://www.ebay.ca/itm/386113212245

Meter in DC volts scale of 5 volts or higher (since this battery new is @ 3v). Place the meter probes across the battery connector on the board. Do not worry about the polarity of the probes.

What is the exact voltage?

We fixed an HP laptop last week and the root cause was this battery. They are $10 on Amazon (Canada). Our original battery was @ 1v5 and should have been ~3v. Start with this measurement and replace it if it is not ~3v.

[BachPhi]

Confirmed.