# The CMOS Checksum is invalid



## trickyrick (Jul 30, 2007)

Good day
I have a laptop that will not boot I have to remove the cmos battery for a min then put it back in and reboot then I get the message below and sometimes can press enter to boot into windows. Once there I have to change my date and Im ok until I shut off my laptop. I have tried to flash the bios with an update but still same problem. I was thinking of trying to replace the bios chip on the MB.
"The cmos checksum is invalid. The cmos will be reset to default configuration and will be rebooted. CMOS Reset (502)


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## tristar (Aug 12, 2008)

Do not replace the chip, replace the CMOS Battery (if it's removable) some laptops have the battery soldered on to the board, so you might require technical assistance if you don't know your way around electronics.


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## trickyrick (Jul 30, 2007)

Thanks for the reply. I have done that. I first checked the old one and it was ok but read a post that if battery is at the end of life it could read 3v but when used the voltage could drop. I replaced it with a new and still the same thing.


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## joeten (Dec 4, 2008)

Hi, could you post the make and model number of your laptop it will give tristar a little more to work with.


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## trickyrick (Jul 30, 2007)

Its a Pavilion dm4 3050us. I did change the keyboard about 8 weeks ago but it worked up untill 2 weeks ago


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## tristar (Aug 12, 2008)

If the battery is located directly under the keyboard, I'd take a look at it to see if it does not slip out while packing the keyboard back in.

If you're ok with disassembling the laptop again, reach up to the CMOS battery, with the power/battery pack & CMOS Battery disconnected, press and hold the power button for a few seconds to release any flea power. leave the CMOS battery disconnected for about 5 minutes then put it back together, most laptops have a socket protection so you can't reverse polarity of the battery without forcing it in, but nevertheless do check the polarity on the board and the red/black wires of the battery or +- terminals and ensure they connect the right way.

Also, I think HP notebooks have a key combination to revert back to the previous BIOS unless you've wiped the hard drive of the HP stuff. In which case, I'd take a look to see if any keys on the keyboard are getting jammed, especially the Fn or Windows Key


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## trickyrick (Jul 30, 2007)

The battery is accessible just behind the hard-drive from the bottom of the laptop. Each time i have to turn on my computer I remove the HD and unplug the CMOS battery. I then hold the power button for a minute and then insert the CMOS battery back in (I might add I also remove AC PWR and laptop battery) I put everything back together and try to restart my laptop. Sometimes it works and sometimes I have to repeat the process 3 times before my laptop will boot into windows. I do notice that for some reason the space bar will stop working I have to press it several times for a space for every word then all of a sudden it will start working again. As for stuck keys Ive tried every one they all look fine


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## tristar (Aug 12, 2008)

Ok, can you disconnect the keyboard, then turn on the laptop and see if it turns on without any issues ?


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## trickyrick (Jul 30, 2007)

Okay I disconnected the keyboard and tried to reboot I come to a message the CMOS checksum is invalid the CMOS will be reset to default configuration and will be rebooted I can't type enter like I usually do at that screen it times out and goes blank I'll have to try to get a USB keyboard


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## tristar (Aug 12, 2008)

Yep, good call, without connecting the base keyboard, connect an external USB, set the BIOS settings for the first time, shut down the laptop and start using the power button.


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## trickyrick (Jul 30, 2007)

Sorry for the delay was on vacation no usb keyboard
Home now
So I started up laptop without keyboard connected only a USB keyboard. Booted up with same message about bios. I hit enter to reboot came up and I changed the date then clicked restart.
Same thing I have to remove the CMOS battery and boot that way. So it does not appear to be the keyboard
Any other suggestions
Rick


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## tristar (Aug 12, 2008)

Ok, then most likely a corrupt BIOS, I know you've tried to upgrade the BIOS, does your manufacturer provide steps to recover the BIOS ? Sometimes there is a key combination to replace with an alternate BIOS image for some it's the Driver CD or a USB flash drive.


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## trickyrick (Jul 30, 2007)

Didnt understand the last part of your reply. Are you saying to put the bios update on a usb drive then use a combination of key strokes at boot up to use the update on the usb drive


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## tristar (Aug 12, 2008)

Ok, so let me elaborate..

Board/PC Manufacturers have an option to 'switch' the BIOS to an alternate version, in the event of a crash, so you might want to check the manuals which provide that key combination as to how you can switch into that alternate BIOS, I think HP uses Windows Key + V/B for the BIOS recovery from where you can recover the BIOS.

Some manu, allow usage of a USB stick (at the rear of the PC) to directly start the BIOS Crash recovery option, others use the Driver CD to do this recovery, so do you know if your Motherboard has a similar feature ?

Once you're able to access the BIOS, check if there are any Dual/Crash Free BIOS settings etc. they contain 2 sets of BIOS, so if the Primary failed, you can start up with the Secondary.

Any chance you know the Motherboard model number ?


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## trickyrick (Jul 30, 2007)

Yes I do
Manufacturer Hewlett Pachkard
Model 1793
Serial Number PCNTA1C2F101M1
Version 41.1E

Ill Try to look up the manual and info on the key strokes
Thanks


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## tristar (Aug 12, 2008)

I think it's Windows key + B or V, better to confirm through the manual.


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## trickyrick (Jul 30, 2007)

Its the windows key plus B
There is a nice video and instructions on how to do it at
https://support.hp.com/ca-en/document/c02693833
When I try it I always get to the screen 
The cmos checksum is invalid. The cmos will be reset to default configuration and will be rebooted. CMOS Reset (502)
So Im not going to be able to use the BIOS recovery.
Im beginning to think Im going to have to shop for another laptop


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## tristar (Aug 12, 2008)

Probably, unless you have a very reliable source who provides BIOS Chips and pre-programs them and is able to re-program in case of issues, it's not a good investment, try flashing other BIOS versions and see if that makes a difference, but high chances you might need a new laptop.


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## trickyrick (Jul 30, 2007)

In your opinion do you think its the BIOS chip. When i re flash the chip it says it was successful. So if the re write is good whats preventing the computer from reading it. BIOS chips pre programmed are only 20 dollars and Im good with a soldering iron. For $20 I would take a chance


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## tristar (Aug 12, 2008)

It's possible, if the chip itself has a bad block, then the checksum will fail. Also, if the crystal oscillator has also failed you might get a similar issue, since the CMOS would revert back to factory state when it detects a multiplier issue.

I'd start with the crystal oscillator/clock crystal first if you're good with a soldering iron.


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## trickyrick (Jul 30, 2007)

Thanks for your help tristar. I think Im going to look for another laptop Ive changed the lcd screen battery and keyboard awhile back its time to kiss it goodbye. 
I have another question you seem to know your way around a computer. How would i disable a motherboard in a desktop temporarily something like soldering a jumper between two legs of the BIOS chip for example. I just don't want it to boot but then later I want to be able to correct the problem.


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## tristar (Aug 12, 2008)

Your request is making me a little apprehensive  If you'd like to disable a motherboard you can leave the ATX and CPU Power disconnected.


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## trickyrick (Jul 30, 2007)

Sorry about that. Let's leave it at that. Thank you very much for your help on the laptop. Have a good day


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## tristar (Aug 12, 2008)

Thanks ! You as well !


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