COURSE TITLE:
PC Hardware and Troubleshooting
PAPER CODE:
CIT 4207
TOPIC:
Troubleshooting and solving CMOS errors;
Objectives:
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Introduction
CMOS display mismatch
CMOS memory size mismatch,
CMOS battery state low,
CMOS checksum failure,
CMOS systems options not set,
CMOS date and time not set.
INTRODUCTION:
CMOS stands for complementary metal-oxide semiconductor (CMOS).
It is the semiconductor technology used in most of today's integrated circuits (ICs), also known
as chips or microchips.
CMOS transistors are based on metal-oxide semiconductor field-effect transistor (MOSFET)
technology.
MOSFETs serve as switches or amplifiers that control the amount of electricity flowing between
source and drain terminals, based on the amount of applied voltage.
The CMOS (Complementary Metal-Oxide Semiconductor) chip stores the settings that you make
with the BIOS configuration program.
To start the CMOS setup process, press the correct key(s) during the bootstrap process or run the
setup program from hard disk or floppy disk after the computer has started.
OR
CMOS is the term usually used to describe the small amount of memory on a computer
motherboard that stores the BIOS settings.
Some of these BIOS settings include the system time and date, as well as hardware settings.
How BIOS and CMOS Work Together
The BIOS is a computer chip on the motherboard like CMOS, except that its purpose is to
communicate between the processor and other hardware components like the hard
drive, USB ports, sound card, video card, and more. A computer without a BIOS wouldn't
understand how these pieces of the computer work together.
The BIOS firmware is also what performs the Power On Self-Test to test those pieces of
hardware, and what ultimately runs the bootloader to launch the operating system.
CMOS is also a computer chip on the motherboard, or more specifically a RAM chip, which
means it would normally lose the settings it's storing when the computer is shut down (just like
how the contents of RAM aren't maintained each time you restart your computer). However, the
CMOS battery is used to provide constant power to the chip.
When the computer first boots up, BIOS pulls information from the CMOS chip to understand
the hardware settings, time, and anything else that's stored in it. The chip typically stores as little
as 256 bytes of information.
CMOS SETTING
When your computer system starts up, the BIOS boot screen appears momentarily. While this
boot screen is being displayed, you can press a designated key to run the CMOS Setup program.
CMOS Setup is used to configure BIOS and chipset settings ranging from those as obvious as the
Date and Time to those as obscure as memory timings and bus settings.
The key that invokes your system’s CMOS Setup nearly always appears on the BIOS boot
screen. If your BIOS boot screen isn't displayed or does not show the CMOS Setup key, try
pressing ‘Esc’, ‘Del’, ‘F1’, ‘F2’, ‘F10’, Ctrl-Alt-S.
CMOS display mismatch
i. CMOS checksum error
A checksum is an algorithm used in many programs to confirm the integrity of a file. This is
used frequently in downloaded programs to confirm the file hasn't been tampered with or
corrupted.
A CMOS Checksum error is a conflict between the CMOS (Complementary Metal Oxide
Semiconductor) and BIOS (Basic Input Output System) that happens when you boot up a
computer.
It occurs when the computer isn't able to read startup information or the data does not match up.
Causes of CMOS checksum errors
A CMOS Checksum error occurs when the computer isn't able to read that information.
1. One of the more common causes of a checksum error is also the simplest to solve.
The battery that powers the CMOS is a watch battery, and it can run out of power.
When the battery is dead, the CMOS can't store information anymore.
2. Power surges and sudden losses of power are other causes.
If a computer doesn't have a chance to write information to the CMOS before it's abruptly
powered off, it has a hard time picking up where it left off. Power surges can also cause
corruption or hardware damage.
3. If the BIOS is damaged or corrupted, it will cause a mismatch between the BIOS and CMOS.
It's uncommon but possible for a virus to infect and corrupt the BIOS. Still, it's more common
that a BIOS update failed or the operating system updated something which caused it to get out
of sync with the BIOS.
How to Fix CMOS Checksum Errors
1. Restart the computer. A normal restart usually creates a new checksum and eliminates
the error. An error lingering after a normal restart requires some more work.
2. Download and flash a BIOS update. Download the update from the motherboard
manufacturer's website. Many motherboards can download an update from within the
BIOS while they're plugged into your network using an Ethernet cable.
3. Reset the BIOS. Some motherboards have a switch either on the board or on the back of
the computer to reset the BIOS settings. If there isn't a switch like that, remove the
CMOS battery from your system for a minute or two. The loss of power causes
everything in the CMOS to reset.
4. Replace the CMOS battery. If the cause is a dead battery, all you need is a new one.
The CMOS battery is located on the computer's motherboard. On desktops, it's easy to
get to, and it's only held in place with a metal clip. On laptops, you'll need to open the
machine up to get to the motherboard, and that might be better left to a professional.
ii) CMOS memory size mismatch
It is normal for a computer to report a memory size mismatch or memory error when memory is
added or removed from the computer.
How to solve this;
When this error is encountered, enter CMOS and ensure the settings for the memory are properly
set and then save and exit from CMOS.
Enter the computer CMOS setup and make sure the CMOS memory settings are properly set for
the amount of memory you have in the computer.
iii) CMOS battery
The CMOS is usually powered by a coin-sized CR2032 cell battery, referred to as the CMOS
battery.
Most CMOS batteries will last the lifetime of a motherboard, up to 10 years in most cases, but
will sometimes need to be replaced depending on how the device is being used.
What is CMOS battery low?
This means that battery failure is incorrect or slow system date and time in the BIOS, loss of
BIOS settings when the computer is powered off, time-of-day clock stopped error message and
so on.
Importance of CMOS battery in setting.
A CMOS battery is like a watch battery that keeps power going to the motherboard enough to
retain its settings. Items like configurations of boot or even the time of the bios are retained
using this battery. These batteries do not last forever so they do need to replace from time to
time.
Steps to replace a CMOS battery
1. Disconnect the power cable of the computer.
2.
3.
4.
5.
Discharge static electricity by pressing and holding the power button for 10-15 seconds.
Replace the battery with the exact same type of coin cell battery. ...
Removing the CMOS battery erases the BIOS settings.
Ensure to replace with a brand new battery.
Causes of low state CMOS battery;
1. Incorrect or slow system date and time
2. Loss of BIOS settings, are major signs of a dead or dying CMOS battery.
3. Another indication of a dead CMOS battery could be a red light on the motherboard.
Replacing the CMOS battery is as easy as swapping out the dead one for a new one.
iv) CMOS systems options not set,
This type of error is often related to the BIOS battery being faulty and the BIOS not retaining the
configuration or a corrupted BIOS.
More probably, this is the CMOS battery that’s not really in good health and not preserving the technical
assistance when the machine is shut off.
How to solve this;
Reset your Default configuration to the original settings by using F10 (to enter it) and also F9 buttons (to
import the presets) during startup, now and save changes and restart.
If the issue reappears, then you’ll need to consider having the CMOS repair done .
v) CMOS date and time not set.
This error simply means that the CMOS battery on your motherboard is failing or is drained.
The good news is that fixing this problem is quite easy – just replace the CMOS battery.
This is a common problem that can occur on any computer.
Common causes of CMOS – Date Time Set error
The CMOS Checksum Bad – Date Time Not Set error can be caused by a variety of things,
including:
– A bad CMOS battery
– Incorrect CMOS settings
– A faulty motherboard
How to solve this error; (date and time settings)
STEPS:
1. Within System BIOS, scroll down using the bar on the right side of the page, then select
Miscellaneous Settings.
2. Click on the System Time or System Date value to adjust the time or date.
3. Once the value is set properly click OK to save the new time or date value, changes take effect
immediately.
4. Once the System Time and System Date are set properly, click the Back button in the bottomright corner.
5. Click Finish in the bottom-right corner to exit System BIOS, then click Finish again to exit
System Setup and allow the system to boot.