Hi Everyone

I have been looking at a computer which will not power up, after some investigation I decided to replace the power supply unit.

After putting in the power supply unit and left it for a few minutes, (you will see the relevance of this when you read through this post) I am able to start the computer, so I shut it down again disconnected all the leads and put the case back on. Just to test the computer worked ok I reconnected all the leads and powered it back up, this is where the problems started again, it would not power up :confused:.

But even wierder, it did power up after a miniute or so of bieng left connected to the power, so I did the following.

1. Shutdown the computer and restarted it again without disconnecting the power lead.
2. Is starts every time now when I press the power on button.
3. Shutdown the computer, unplugged the power supply from the mains, plugged the power back into the mains.
4. Same problem again, the computer would not start until it had been connected to the mains for at least one minute and then it would start again everytime, so obviously there is some issue when the computer is siwtched off at the mains.
5. So now I opened up the case again, and unplugged everything off the mohterboard except for the PSU and scable to the power on button.
6. Still the same issue i.e. takes over a minute to start up after bieng disconnnted from the mains power supply, but then continues to start ok until the mains power is disconnected.
7. Now starting to get annoyed, I installed yet another PSU from another computer which I know works fine, but the same thing happens.
8. I also have replaced the power on button, with no success.

The only common factors I can find are are disconnecting from the main power supply causes a big start up delay and the motherboard is the only part in every test.

I am pretty sure that the motherboard has developed a fault and being a older computer I suspect I will not be able to get a replacement which costs less than the actual value of the computer.

Have I missed anything or does anyone have ideas.

Thanks

Slim

Go into the BIOS and see if there are any options for "power on after". It could be that because you are unplugging it and there is now voltage anywhere that it thinks there has been a power failure and is going through some sort of recovery phase from a power failure.

If the 'mains' that you're referring to is the main PS-to-MB connection, then it's possible that one of the connectors is defective.

Raise the PS connector just a little, and see if that stabilizes things. If so, then the metal pins/sleeves in the connectors are not making proper contact.

Mjc - I have checked all the bios settings they all look ok and since nothing was changed on the computer before this started happening, I do not suspect that to be the cause.

Ski - The mains I am referring to is from the wall socket to the PSU and I have checked all the connections.

Interesting, I also found that when the computer does start, it will hang and just turn itself off after around a minute of running.

As this problem came on suddenly, I suspect some sort of failure on the motherboard.

Slim

If all of the connections upstream of the computer are reading the proper voltage, and the power supply module's selector switch is set to the correct voltage, then bypass the surge arrestor.
If that does not work, then remove the MB and place it on a piece of cardboard.
If that works, the check for a ground between the MB and the case. The most likely cause will be either a metal standoff or screw contacting a MB circuit trace. Placing paper washers(manila folder paper works excellent) between the MB nad the screws and standoffs. Also, check for a loose screw, etc. laying in the case.
If no luck, then it may be a bad MB.

Ski,

As suggested I removed the motherboard from the case and tested it.

But it still will not work, so it must be a faulty motherboard. As the computer is over three years old it doesn't seem worth repalcing the motherboard, that is assuming I would be able to get a suitable replacement.

I think I will just put this computer to one side and use it for spare parts for other similar computers.

Thanks for all your help

Slim

You're welcome, slim.
It's too bad that your situation did not have a happier ending.