it is booting whenever the power to the PSU is connected

This is unclear. Are you suggesting that you cannot turn the system off, and that it keeps coming back on whenever you try to shut it down? That sounds like it might be an issue with the power switch in your case.

Otherwise, perhaps you have the "resume on power failure" option toggled in your BIOS?

Some boards have BIOS setting what should it do after power outage, you might want to check that.

Also if the CMOS battery is running low, and when 5V standby voltage fades away, battery might not keep the chipset RTC clock ticking even if it preserves settings.
When there is no clock in the chipset, it does not know what to do when 5V standby supplies reappear and decides to turn on the PSU. Measure battery voltage or try replacing it.

Jorpho wrote:

it is booting whenever the power to the PSU is connected

This is unclear. Are you suggesting that you cannot turn the system off, and that it keeps coming back on whenever you try to shut it down? That sounds like it might be an issue with the power switch in your case.

Otherwise, perhaps you have the "resume on power failure" option toggled in your BIOS?

No. It has nothing to do with shutting down. I am talking about the power from the wall socket being cut off.
And when i turn on the 220 volt to the PSU, then the machine starts to boot.
I have solved the issue I had with powering down the system, as it had some quirks.
Shutdown procedure has no issues at all.

The "resume on power failure" or "power loss restart" as it is called, are set to "disable" in the BIOS.

Jepael wrote:

Some boards have BIOS setting what should it do after power outage, you might want to check that.

Also if the CMOS battery is running low, and when 5V standby voltage fades away, battery might not keep the chipset RTC clock ticking even if it preserves settings.
When there is no clock in the chipset, it does not know what to do when 5V standby supplies reappear and decides to turn on the PSU. Measure battery voltage or try replacing it.

Ahhh.... That have never crossed my mind. Going for a battery replacement, to see what happens.
It might be what is causing the issue, as the problem appears after the system have been shut down for 10 to 15 minnutes.

Hmmm....
It was not the battery. 🙁

Does it still happen if you disconnect the power switch on the case?

Jorpho wrote:

Does it still happen if you disconnect the power switch on the case?

The isuue is still there, with and without the powerbutton connected to the front-header panel on the motherboard.
I tested it when I woke up today, so it have been resting a whole night.

I have seen this before, just that I can not remember how I solved it, as it was 10 years back in time.
And the issue was on those P4/Athlon64 systems, and not K6 systems.

Does the clock still run when it is powered off? Or do you need to readjust it every boot?

alexanrs wrote:

Does the clock still run when it is powered off? Or do you need to readjust it every boot?

Nope. It still runs perfectly. No issues there. When I get another PSU for my test-bench, then I can say if it's the PSU or not.
Other than that, I really want to know if people have had this issue with other boards, and how they resolved it.

If it is the PSU, how can I test the +5volt and -5volt rails out? As it was mentioned, that the standby is 5volt?
Or is this of no use to test out? I mean... If the PSU is bad on one of those rails, could it produce this problem on the Mobo?

My p2b system does the same thing,runs perfectly fine and shut down works as it should but as soon as i turn the power on it starts booting. Don't know why.

I have an msi 5169 ss7 board which does the same thing...

Always thought it was the battery but didn't try a new one yet. Maybe bios flash?

meljor wrote:

My p2b system does the same thing,runs perfectly fine and shut down works as it should but as soon as i turn the power on it starts booting. Don't know why.

I have an msi 5169 ss7 board which does the same thing...

Always thought it was the battery but didn't try a new one yet. Maybe bios flash?

I see.... They might just have been built this way.
If this is of no real issue regarding usage, then I just have to suck it up and move on. 😁

Yep my Asus P5A mainboard does the exact same thing. I don't know why either. Which is a bit of a bummer because I always turn of the mains at night via remote. When I turned the mains on the computer turns on right away. 😖