Motherboard not POSTing unless cmos cleared




I've read a number of posts from pepole with similar (but not same) problems and so far no solution has helped me yet, so I decided to ask the Tom's Hardware comunity if anyone had any other experiences or suggestion...

I have an old computer with an Asus A8N-E motherboard that just recently started displaying this problem, after running for years without even a hiccup. The computer was shut down properly, but the next time it would not start up again (there was absolutely nothing done on the computer in the meantime). There was no POST, no display and no beep on the speaker, but the fans start, harddrives are started up, DVDs are started up. I know this problem has often been discussed on this board, however there's something different in my case. I managed to start up the board completely by clearing the the CMOS data AND not saving any setup in the BIOS setup. This way I can boot the machine, run test programs and the OS (memtest86, start Ubuntu completely) without any error ... it can run for hours without any issue. Yet the next time I reboot the machine it will again not even come to POST.

The same thing happens if I enter BIOS and save any settings (doesn't matter whether it's default settings or anything else).

So, the machine doesn't come to POST if:
Compute is switched on, the CMOS battery is present and the computer was previously switched on
Computer is reset (hard reset, soft reset, doesn't matter)
Exiting BIOS by "save changes" (a reset is the performed which then hangs the computer)

The computer does start if:
Computer is switched on after performing a CMOS reset
Computer is switched on after the power has been disconnected and reconnected (or OFF/ON shitch on the PSU) and there is no CMOS battery inserted
Exiting the BIOS by "discarding changes" - also performs a reset, but does not hang the computer !!

Do you think there's anything that could be done about this issue or is CMOS gone ?


Thanks for the thought, I don't. The old battery has a good voltage of 3,0V. Besides as I wrote earlier: I can make the computer start without the battery if I shut down the PSU supply, while it never starts if the battery is inserted (unless I clear the cmos settings before inserting it). And the computer doesn't start after a reset whether there is or isn't a battery inserted, hence I deduct that the battery has no relevance on the startup problem in this case (If I'm right the battery is actually not used if the PSU doesn't loose it's power anyway).

Anyway, I had a spare (completely new) CR2032 battery at hand so just to make things sure, I tried exchanging it and it made absolutely no difference.


Here are the Voltage measurments, but there doesn't seem to be anything strange to me, maybe someone else knows better:

Voltages are as follows (OFF, ON not reaching POST, ON running Ubuntu)

Purple Wire 5,07 / 5,06 / 5,05
Green Wire 4,61 / 0,04 / 0,04
Gray Wire 0,00 / 5,14 / 5,12
Orange Wire 0,00 / 3,32 / 3,32
Red Wire 0,00 / 5,13 / 5,11
Yellow Wire 0,01 / 12,16 /12,12

The Green wire coltage might be a little off , but it is the same in off ode before the computer is about to start normally (after cmos reset or after repowering the PSU without a cmos battery) and before it is powered on without POST (after a software shutdow).