I once had a Soyo board that wasn't saving the settings after I replaced the CMOS battery and the problem turned out to be some difficult to see corrosion on the coin cell holder's contacts. I checked the coin cell holder's contacts on the back of the motherboard and had no voltage. Worth it to check that if you haven't already.

Thanks, but already checked that by way of via's

The only chip on the board I can see that may save bios settings is the ASUS ASIC, but there isn't much in the way of datasheets out there for this AS97127F. Unless, is part of the Southbridge?

From the little info I can find, I think it's part of the Southbridge IC. When powered off, if I isolate the +ve terminal of the battery tray from the Cell using paper, and check for current flow, from the cell to the terminal, I don't appear to have any current passing. I'll see if I can find any more trace faults on the board, but that all seems good on this one, maybe even try to reflow the solder, although I'm not overly keen on doing this on a 25yo BGA Chip!

Macsbig wrote on 2025-08-25, 22:28:

Hi all, […]
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Hi all,

Does anyone know which IC on this board houses the CMOS RAM?

I've aquired a board that wouldn't post (sorted that, re-soldered the Winbond i/o chip), but now if I power up after a power off I get bios checksum error - defaults loaded.

I changed the CMOS battery but made no difference. I'm not really sure where the settings are being saved, if I can find that out, I can do some fault finding.

If I just reboot, settings stay in bios

Cheers, Mark

The settings are stored in the BIOS Flash ROM. The symptoms you describe suggest that you system can't write the ESCD to the BIOS chip.

Dorunkāku wrote on 2025-08-26, 10:50:

Macsbig wrote on 2025-08-25, 22:28:

Hi all, […]
Show full quote

Hi all,

Does anyone know which IC on this board houses the CMOS RAM?

I've aquired a board that wouldn't post (sorted that, re-soldered the Winbond i/o chip), but now if I power up after a power off I get bios checksum error - defaults loaded.

I changed the CMOS battery but made no difference. I'm not really sure where the settings are being saved, if I can find that out, I can do some fault finding.

If I just reboot, settings stay in bios

Cheers, Mark

The settings are stored in the BIOS Flash ROM. The symptoms you describe suggest that you system can't write the ESCD to the BIOS chip.

Sorry Dorunkãku, but this is an often heard misconception.
The 4KB ESCD block in the BIOS flashchip is only used for storing Plug&Play data.
The BIOS Setup data is stored elsewhere.

The Asus P2B board uses the i440BX chipset, where its Southbridge houses the Real-Time Clock and 256 bytes of battery-backed CMOS SRAM. This is where the BIOS Setup data is stored.

Jan

Thanks for confirming my suspicions Jan. Although it probably means this board is a test board only.