View Full Version : ATX cycling fault?

07-12-2011, 12:28 AM
I've just dragged an old ATX type Dell out of the cupboard with the intent on getting it ready to use with Mach 3.

It's doing something weird, about 3 seconds after applying mains power it stops and restarts.. I've tried disconnecting all drives etc, everything but the motherboard, it still does it.. The fan on the power supply is stopping and starting at the same times. I'm thinking the power supply has died, there's no fancy motherboard sensing stuff in an ATX power supply is there? Any thoughts most welcome!

07-12-2011, 07:13 AM
Not sure Mocha but I have a old power supply if you need it


Jon S
07-12-2011, 08:27 AM
about 3 seconds after applying mains power it stops and restarts.

YES ATX has control of the power supply, so it really does not sound like there is an issue with the PSU.

There should be an option to display Power On Self Test results to the screen, and to perform all the BIOS POSTs. It does want to and is trying to tell you what is wrong with it.

"Some older Dell computers use an alternate key sequence instead of <F2> to enter System Setup. These key sequences include:

<Fn>+<F1> (laptop computers only)
<Fn>+<Esc> (laptop computers only)"


First you need to know that the CMOS memory (that stores all the BIOS settings) has not been corrupted or blanked due to the battery cell on the MB not being charged in use or just demise from natural causes.

Get into the BIOS and be sure that the HDD(s) are configured.

Clearly an awesome opportunity to get an Apple :-)


Jon S
07-12-2011, 08:40 AM
either my "advanced reply" has got lost or it is being moderated - so not sure if this will end up as a double post :-(

ATX MB do control ATX PSUs - this was the primary reason for the migration from AT to ATX.

Thereby it does not sound like it is a PSU issue although there are complex (to me) ways for a PSU to fail.

After an extended time not in use the CMOS battery that enables the CMOS to store critical info can have failed or discharged and hence the BIOS cannot read the CMOS to find where to boot from..

F2 is the normal Dell setup button, you need to get into the BIOS setup and check that your HDD are configured.

The POST is trying to tell you what is wrong, if you can track down the info on the Dell support web site for your MB.


07-12-2011, 01:52 PM
There is one pin on the PSU which acts as an enable. Perhaps try measuring the voltages from the PSU to verify that none of them are outside tolerances, just in case?

I had an old computer recently that did what you described. Turns out it was the processor than had died.

Clearly an awesome opportunity to get an Apple :-)

Why would anyone do that.

07-12-2011, 02:01 PM
Many thanks guys,

Thanks for that JonS, nice link!

According to the diagnostic lights mentioned in the 2350 doc, "Memory modules are detected, but a memory failure has occurred.."

EDIT: I pulled the memory and got beeps! memory back in and no beeps, power supply stays on! Looks like a badly seated memory module was causing the problem. Now I'll put it all back together and see what other surprises it has in store for me! :-)

I did suspect the Bios battery might have failed, hence the question about some etherial connection between them but when that has happened in the past, I'm fairly sure that it still got as far as letting me get to the bios info... I'll have a better look later..

@James; could you apply mains power to your power supply and tell me if the fan spins up - (and stays spun up) without anything connected to it please? That might resolve another issue for me!

Thanks guys! looks like I might be in business! :yahoo::yahoo:

Jon S
07-12-2011, 02:06 PM
Why would anyone do that.

For an easy life :rolleyes:

07-12-2011, 02:08 PM
Clearly an awesome opportunity to get an Apple :-)


S'funny you should say that! lol... I just recently bought an apple too! lol