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HP Pavilion 21-a000 All-in-One Desktop PCs - Replacing the CMOS Battery

This document applies to HP Pavilion 21-a000 All-in-One desktop computers.
HP Pavilion 21-a000 All-in-One desktop computer

Before you begin

CMOS factory settings should be restored as a first step before replacing the system motherboard. To restore the CMOS factory settings, replace the CMOS battery.
  • You need a Phillips head screwdriver.
  • You need a flat head screwdriver.
  • Turn off the computer. Disconnect the Ethernet or modem cable. Disconnect the power cord.
  • Transfer the computer to a clean, flat, stable work surface over a noncarpeted floor. HP recommends that you put down a blanket, towel, or other soft cloth to protect the screen from scratches or other damage.
  • Electrostatic discharge (ESD) can damage your processor, disk drives, expansion boards and other components. HP strongly recommends the use of an antistatic wrist strap and a conductive foam pad when working on the computer.
  • Do not remove a component from its protective packaging until you are ready to install it.
This product contains components that can be damaged by electrostatic discharge (ESD). To reduce the chance of ESD damage, work over a noncarpeted floor, use a static dissipative work surface (such as a conductive foam pad), and wear an ESD wrist strap connected to a grounded surface.

Video overview

View the following video before using the steps in this article.
For best quality on dial-up connections, wait until the video has fully loaded before viewing.

Removing the CMOS battery

If the computer clock is losing time, change the CMOS battery. After replacing the battery with these instructions, it is necessary to reset the clock in the BIOS.
Use the following steps to remove the CMOS battery:
Step 1
To remove the CMOS battery, first remove the rear cover.
For instructions to remove the rear cover, see the HP support document, Removing the Rear Cover.
Removing the rear panel
Step 2
Next, remove the motherboard EMI shield. To remove the shield, remove the two screws that secure the shield to the frame.
Removing the two screws
Step 3
Tilt and lift the shield off of the motherboard.
Lifting the motherboard from the computer
Step 4
Find the CMOS battery.
The CMOS battery
Step 5
To remove the CMOS battery, pry it up out of its socket...
Prying the battery out of its socket
...and lift the battery off the motherboard.
Wait at least thirty seconds before replacing the battery.
Removing the battery

Replacing the CMOS battery

Wait for thirty seconds before replacing the CMOS battery using the following steps:
Step 1
To replace the battery, insert the battery in the same orientation, with the writing facing the same way as it was on the battery that was removed.
CMOS factory settings are now reset.
Note that you will now need to enter system BIOS and reset the clock in BIOS after this procedure.
Replacing the battery
Step 2
To replace the motherboard EMI shield, find the alignment tabs on the shield...
Finding the alignment tabs on the shield
...and the alignment tabs on the frame.
Finding the alignment slots on the frame
Step 3
Align the tabs into their slots, then press the shield down into place.
Placing the EMI shield back down on over the motherboard
Step 4
Replace the two screws to secure the motherboard shield to the frame of the computer.
Two screws that secure the shield over the motherboard
Step 5
For instructions to replace the rear cover, see the HP support document, Removing the Rear Cover.
Removing the rear cover






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