Elitebook 850 G8 - 5 slow CapsLock flashes & no boot

[Momolar]

Hello,

I have recently switched the motherboard of my HP Elitebook 850 G8 to upgrade the processor. The part is new.

Now, when trying to turn the laptop on, the laptop does not boot and the screen remains black.

The fan spins for about 1 second, then the Caps/NumLock both flash 5 times, white.

The fan then spins again for 1 second. Then nothing.

I have tried booting without the camera / keyboard / speakers / etc connected, but still get the same error.

I have tried disconnecting battery and pressing power button for 30s. I have tried booting with only the charging cable and no battery. Nothing changes.

I have also tried booting without the RAM memory, to see if I get the same error code. When I do, I get audio beeps and a different error code. So that rules out faulty RAM, correct?

I'm at a loss. I don't know what the issue could be.

Furthermore, no information about such error codes can be found online. The only page I find only mentions error codes starting with "2 red flashes". I have never seen a red flash on my laptop.

Any help appreciated.

[TejaswiniM · Accepted solution]

Hi @Momolar .Welcome to HP Support Community!

The blinking white caps lock and num lock lights, flashing 5 times on your HP Elitebook 850 G8 after a motherboard replacement, indicate a hardware fault with the system board itself. Since this is a new board, it suggests an issue with the part, an incompatibility, or a problem with another component that is now exposed by the new board.

What the 5 white flashes mean
For modern HP business notebooks like your Elitebook, the caps lock LED uses different flash codes to communicate hardware errors during the Power-On Self-Test (POST).
A pattern of five white flashes signifies a generic system board failure, which means a critical component on the motherboard is not functioning correctly.
Your testing without the RAM, which produced a different error code, correctly eliminated the memory as the root cause of the 5-flash code.

Potential causes after motherboard replacement
Faulty replacement part: The "new" motherboard you received may be defective. This is the most likely cause, as it is failing its own internal checks immediately upon power-on.
Incompatible processor: While the board was replaced to "upgrade the processor," it's possible that the new CPU you are attempting to use is incompatible with the specific version of the motherboard, its firmware, or a required voltage regulator. A motherboard with a different processor generation will likely cause this kind of boot failure.
Corrupted BIOS or firmware: The BIOS firmware on the new motherboard may be corrupt or was not properly initialized during manufacturing. This would trigger a system board failure code.
Improper component installation: Though you have tried booting with minimal components, there could be a delicate connection that was not properly seated. This is especially true for the display cable, power button board, and other flex cables that are easily damaged or misaligned during installation

You can also try the steps below-

1. Check compatibility: Before proceeding, verify that your new CPU is fully compatible with the specific Elitebook 850 G8 model you have and the replacement motherboard you acquired.
2. Inspect all connections: Carefully open the laptop again and re-examine every single cable, ribbon, and component connection.
   • Processor socket: Remove the CPU, inspect the socket for any bent pins, and then re-seat it carefully.
   • Ribbon cables: Reseat all ribbon cables, especially the one for the power button board and the display.
3. Run HP BIOS recovery: You can try to recover the BIOS using a USB drive. This procedure can sometimes resolve issues with a corrupted or mismatched firmware.
   • Download the latest BIOS file for your specific Elitebook 850 G8 from the HP Support website.
   • Create a USB recovery drive using the HP utility.
   • Plug the USB drive into your laptop and boot it while pressing the Windows + B keys.
4. Test with the old processor: To isolate the problem, try re-installing your original processor into the new motherboard. If the system boots correctly, you'll know the issue lies with the new processor. If it still fails, it confirms the replacement board is at fault.
5. Return the motherboard: Given that the motherboard is a new part and the error is a critical "system board failure," the most direct solution is to contact the seller and request a replacement. Provide the error code and steps you have already taken

Hope this helps! Keep me posted.

[Momolar]

Thank you for the detailed answer. This is perfect.

As I am not able to return it, I decided to inspect it myself.

I have tested all the power rails throughout the POST sequence, and all seem stable and correct.

There also doesn't seem to be any physical damage on any components / traces.

I was starting to lose hope until you mentioned firmware, so I might look into that now. I didn't know it could cause the 5-blink error as I believe BIOS has its owns error code?

Thanks again for the help.