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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.

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.

caution:
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.

note:
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.
Step 2 Next, remove the motherboard EMI shield. To remove the shield, remove the two screws that secure the shield to the frame.
Step 3 Tilt and lift the shield off of the motherboard.
Step 4 Find the CMOS battery.
Step 5 To remove the CMOS battery, pry it up out of its socket...
...and lift the battery off the motherboard. Wait at least thirty seconds before replacing 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.
Step 2 To replace the motherboard EMI shield, find the alignment tabs on the shield...
...and the alignment tabs on the frame.
Step 3 Align the tabs into their slots, then press the shield down into place.
Step 4 Replace the two screws to secure the motherboard shield to the frame of the computer.
Step 5 For instructions to replace the rear cover, see the HP support document, Removing the Rear Cover.

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