BIOS losing settings

  Pine Man 15:45 18 Jan 07

I have been doing some work on a friends computer and he told me that, despite not having a floppy drive, if the computer has been disconnected from the mains completely (not just switched off), when he boots it up he gets a CMOS error (40) because the floppy cannot be found.

I changed the BIOS settings to disable the floppy drive leaving just the CD ROM and HD with the HD first in the boot sequence.

When I re-booted the computer everything was ok. I then turned it off and re-booted and everything was ok. Next I turned it off, disconnected it from the mains for about a minute then re-booted it and got the CMOS error (40)!!!

On checking the BIOS I find that all of the settings that I had changed had been reset to what they were and the date had been reset to 1-1-2003, which was probably when the motherboard was manufactured.

The BIOS is Phoenix Award and apparently the computer has done this since my friend bought it!

It sounds like a battery problem but how can that be affected by disconnecting from the mains but not by just turning off the computer?

  ed-0 15:54 18 Jan 07

It is because the base unit still draws a very small current to the motherboard. This by-passes the motherboard battery and keeps the bios settings. Take the power adapter out of the electric socket and you get no trickle to the motherboard. So the motherboard has to rely on the bios battery, if the battery is flat, you loose the bios settings.

  john-232317 15:56 18 Jan 07

I had a similar problem when I replaced a MB that had been in stock for a long time,that kept losing the settings so changed the battery, now fine.

  Pine Man 16:07 18 Jan 07

Thanks very for your prompt replies - I'll change the battery.

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