HP Elitebook 840 G4 - boots only if CMOS-battery is disconnected

[diaz0815]

Hello!

I got a damaged HP Elitebook 840 G4 from a friend of mine where I replaced the broken display. But when I push the power button the display stays black, the fans are spinning and the LED's from the keyboard lights up. I figured out how I can boot the OS:

• remove the internal battery
• remove the CMOS-battery
• remove the charging cable
• push the power button for at least 10 seconds
• connect the charging cable
• push the power button without reconnecting the internal battery and CMOS-battery

After this procedure the display turns on and a warning message concerning a faulty RTC caused by the missing CMOS-battery appears. The fans starts spinning.

Now I have to opions, the first is to accept the message with enter and boot the OS or while the message is on the display I can reconnect the internal battery and the CMOS-battery while the laptop is still running and after that boot the system.

But that is not the solution for a long term use. Every time the laptop is completely off for a few minutes I have to repeat this process to start the system.

I have checked the RAM and the SSD with replacement parts, I measured the voltage of the CMOS-battery, I reinstalled Windows 10 x64, I installed Linux in parallel to Windows, I disconnected the touchpad from the motherboard, I upgraded to the latest BIOS-version a few days ago, all drivers are downloaded from the HP support site for the laptop model.

So to summarize it, the laptop only starts when the CMOS-battery is disconnected and the system is fully discharged.

Does anyhone had similar problems with a laptop?

Thanks for your replies

Patrick