Bad power switch on pc?

[ddrumman2004]

I have been going round and round with my 6 year old desktop that has recently taken to just shutting off. No error messages at all.
Suspecting the power supply, I bought a new one with more power as I figured the original PS had seen better days as the computer stayed on most of the time. Plus, it had a slight burnt smell from the cooling fan and components on the internal board.

The new power supply worked fine until I turned the pc on this morning. It shut down after a minute or so then refused to do anything when front power switch is pressed. It did come on, however briefly once then nothing.

I reset BIOS by removing battery and then decided to try shorting the two prongs that the switch connects too.

Presto! On it came! So I shut it down, removed the connector for the power switch and my meter shows it making connection when pressed. But hook that switch up and it won't come on at all....nothing. Short those two prongs and on it comes.

So I guess I'm asking is that can a switch act like this....like show it making contact when disconnected? But not work when connected up?
Are these switches designed for a certain amp or ohm load when starting the computer?
This is just a momentary contact switch and I do measure some slight resistance when checking it out.

Any thoughts?

 

[calvin1]

The resistance should be infinite when not pushed and close to zero when pushed. Anything else is highly suspect. The load they carry is tiny, probably nothing more than TTL if that.

The real test would be to see how it behaves with the switch disconnected from the mobo. Boot the unit by shorting the two jumper pins and see if it shuts itself off later even though the switch isn't connected.

 

[Quest]

Aside from testings/verifying that the actual power switch is indeed establishing connectivity when pushed, mind you though:

starting from mid/late 586 days and beyond: powering up switch is no longer by means of a hardware switch but driven by chip on mobo.

And when the mobo is on it's brink of failure, the powering up may suffer also (even with a properly functioning HW switch and brand new PSU).

I wouldn't be surprised if your mobo is about to go.

Q.

 

[ddrumman2004]

I think I found the problem.
I pulled the front of the case off to see if I could short the terminals on the power switch. Nothing happened.

So in trying to remove the connectors to the reset switch below, the computer came on.

It did boot when shorting the prongs on the motherboard so in trying to determine if the wiring was bad, the thing came on when fiddling with the switch wires.

Is the reset switch a normally open switch as well?

 

[calvin1]

Originally Posted By: ddrumman2004
I think I found the problem.
I pulled the front of the case off to see if I could short the terminals on the power switch. Nothing happened.

So in trying to remove the connectors to the reset switch below, the computer came on.

It did boot when shorting the prongs on the motherboard so in trying to determine if the wiring was bad, the thing came on when fiddling with the switch wires.

Is the reset switch a normally open switch as well?
Yes, both are normally open.

 

[Carbuff]

Make sure the cooling fans are working OK.



I had a PC once that shut off---it was overheating because the cooling fan (not the CPU fan) was not working.

I swapped the fan's plug to a different plug on the motherboard and the fan and 'puter worked fine for years...

 

[eljefino]

You might want to get into your BIOS... NOW! and look for an "under power failure" setting... There will be something that where it sees power at the mains plug it boots itself.

Then you can plug the whole mess in a power strip, and use the strip switch, or if you have one the one on the back of your PSU.

 

[Jakegday]

Originally Posted By: Quest
Aside from testings/verifying that the actual power switch is indeed establishing connectivity when pushed, mind you though:

starting from mid/late 586 days and beyond: powering up switch is no longer by means of a hardware switch but driven by chip on mobo.

And when the mobo is on it's brink of failure, the powering up may suffer also (even with a properly functioning HW switch and brand new PSU).

I wouldn't be surprised if your mobo is about to go.

Q.


this made sense, until i thought: that motherboard doesnt know the difference between being jumped, or turned on with the swtich...

although it would make sense for a mobo to be failing after years of being turned on. regardless, i'd start backing stuff up ASAP

 

[ddrumman2004]

To all.....it's the wiring to the main switch and reset switch. The computer has been up and running for a while now with a CPU temp of 95 degrees F.

Heat is not a problem as there are 5 case fans running, the largest a 5" fan....as well as the CPU fan.
The Asus Monitor program shows all is well as far as voltages, temps and fan speeds.

When I attempted to install the front back on the case, as soon as I snapped it in place, it shut down. I pulled the front back off and pressed on the wiring to the reset switch and it booted back up!

I shut it down to put the side back on and buttoned it up and she fired back up when I pressed the switch.

Thanks for the replies but it's running fine now.