Strange Boot Failure - Why?

My desktop PC (Gigabyte GA-Z77X-UD5H) failed to boot yesterday. There was no video output nor an error beep although the power on LED was lit. Power to the motherboard was good but the boot hung with error code d6 which is No Console Output Devices are Found.

I removed the Sapphire GPU to try the onboard Intel GPU and had the same error. I then removed the CMOS battery which showed 3V and replaced it with a new one showing 3.2V. This would also set the BIOS to default values. The PC then booted so I loaded the BIOS defaults then reset my BIOS settings. All is now fine.

I'm mystified why this happened - any ideas? Did the low CMOS battery voltage corrupt the BIOS data in some way (but a dud battery usually just results in the date/time being reset)?

CountMike said:

It's most likely you had some BIOS/UEFI corruption and by removing battery it was back to defaults. Battery should be good to about 2.9v but clock itself may work at even lower voltage. To keep other settings takes higher voltage.

What would cause a BIOS corruption? Perhaps a spike on the power line or a cosmic ray?

CountMike said:

Or UEFI partition.

Please explain. The boot failed mid way through the boot process well before any attempt was made to load Windows.

Apologies for resuscitating this old thread but I just had the same problem & solution as post 1 on my Gigabyte GA-Z77X-UD5H motherboard.

The PC was fine yesterday. Today it failed to boot with no display or BIOS screen. The board showed error code d6. Resetting the BIOS via the switch on the motherboard didn't work. I then replaced the CMOS battery which had dropped to 2.8V and all is fine again.

I hope this helps anyone having a similar problem. Normally I expect to see an incorrect time / date if the CMOS battery has expired but on this motherboard a voltage drop on the CMOS battery below a certain level seems to result in sudden death!

Ztruker said:

You're measuring the battery voltage with a multi-meter but that doesn't really put a load on it. Under load it may be providing less, maybe much less than 2.8V

Good point about me measuring the voatage open circuit but surely the current load on a CMOS battery is really tiny?