CMOS checksum is invalid (CMOS reset 502) due to a CMOS battery exchange

[Technival-IT]

Hi,

Since a standard CMOS battery exchange (for a brand new one), after each disconnection of the unit from the power source (power cable), the computer displays the message "CMOS checksum is invalid (CMOS reset 502)".

The problem occurs ONLY when the unit is completely disconnected from a power source, otherwise, the computer is booting normally and all the BIOS parameters are saved.

The computer is acting like the CMOS battery is defective.

I tried with another tested 3.3V CR2032 battery but the problem remains.

I followed every steps discribed on HP knowlage database in general and specific tutorials.

I successfully reset the CMOS by booting the unit on the SW_CMOS jumper configuration.
I updated the BIOS to the update rev. 843B vF.49 10/24/2022.

I'm a little bit out of options, so if you have a clue, I'll be glad to try something to fix this issue.

Thanks

[erico]

"another tested 3.3V CR2032 battery"

Tested?  Not a new battery?

[Technival-IT]

By "another tested 3.3V CR2032 battery" I mean another new CR2032 battery that I tested on multimeter just to be sure.

[erico]

I would remove the motherboard and troubleshoot,  using a multimeter set on voltage, the portion of the power rail circuit that goes from the CR2032 battery holder to the BIOS chip.

There may be an issue, perhaps a component,  MB trace or solder connection fail from where the power is supposed to go from the battery to the EEPROM  BIOS chip.

[ci7alex1]

I am experiencing the same with a relatively fresh All in one HP unit at mom's. No way a CMOS battery life is the culprit here. I attribute it to a BIOS firmware update which I installed as the HP support tool requested not long before the PC started playing up. Judging by the amount of similar issues all over the internet with HP units, I would not be surprised this warrants a mass recall.

[erico]

@ci7alex1 
" I installed as the HP support tool requested not long before the PC started playing up"

I think what you stated indicates that the issue, in the case of your PC was preexisting, according to what you said.

Perhaps you should start your own thread and supply details, including the system SKU, operating system and the exact symptoms you are seeing.

"relatively fresh" is a rather vague description.

Can you provide more precise information than that?

[Technival-IT]

I've removed the motherboard and I tested the power circuit rail between the CR2032 bat to the BIOS Chip.

I've read the BIOS chip on a BIOS chip reader (Asprogrammer) and compare original and new BIOS.

I've looked at the board itselt looking for a bump, scratch or some, testing MOSFETS, resistors around some critical areas.

Everything looked normal, stable and untouched. No alterations whatsoever.

Maybe a schematics and boardview of this specific motherbard might help to follow the power rail and check for good componement mesures. Infortunatly I couldn't find any.

If you have such files (or link to it) or some ideas,  i'll be glad to continue my investigations further more. 

Thx

[erico]

Try restoring the BIOS.

With the power adapter plugged in and the power off, press and hold the Windows key and the B key at the same time, and then press and hold the power button for  either thirty seconds or a response from the laptop that says "recovering BIOS".

At that point you can release the keys and wait for the process to finish.