Hello Nathan, and thanks for the question.
This is a very interesting question, and one I have enjoyed
researching. Fortunately, the ATX power supply unit is a pretty
standard unit. There are several sources which will tell you where
the PSON wire is (Typically coloured green on most PSU's, although
Dell appears to colour it differently - see below).
The first article I came across is:
CK42's CPU Over-Temp Detector / PSU Shutdown How 2 Instructions -
This page is dealing with inserting a thermal temperature sensor under
the CPU, and then using the PSON signal to shutdown the PSU if that
goes above a certain point - in other words, to cut the wire using a
relay. It deals with finding the PSON wire, the voltages used, and
similar things you would need to know. Broadly related to your
requirements, it includes quite a bit of background information on the
PSU that is helpful when working out exactly which wire to attach to
The second article I came across is:
Technical Overview: Dell Dimension XPS Txxx and Txxxr Systems
Aproximately 3/4 of the way through this document, there is a section
entitled, "DC Power Connector Pin Assignments" which informs us that
this particular Dell PSU has a brown PSON# wire, on pin 11. It also
"Pin 11 - PSON# is activated by pressing and releasing the power
button while the power supply is in standby state. Activating PSON#
connects the power supplys PSON# input to ground, thereby switching
the power supply to full-on condition."
This suggests that the PSON needs to be connected to ground to turn
the power supply on, either through a switch or by hard-wiring the
PSU Power On Signal
Dell PSON color
After reading about power supplies and motherboards, I would like to
interject a small not of warning here. Since you say the system is
expendable, it is not such a major thing, but many motherboards
include a self-test system in the BIOS and elsewhere, and it could be
that the motherboard is not sending the PSON signal to the PSU because
it is somehow failing the self-test. Having said this, it could be
that a ground-link or similar has come loose, or that a relay has
seized in the off position.
I hope you manage to sort your system out, and that these articles and
comments have been of help to you.
Request for Answer Clarification by
08 Aug 2002 09:43 PDT
Thanks for your very insightful answer. It seems to have helped.
As the site http://support.jp.dell.com/docs/systems/dkub/techovu.htm
you recommended noted, Pin 11 is the power on pin (it is gray rather
than brown on my Dell PS-5141-1D power supply, but still Pin 11).
When I connected Pin 11 to ground (Pin 12), the power supply does
comes on and it gives power to all the other connectors. At first, my
motherboard didn't boot when power was applied, but after fiddling
with it, the system kinda works! The regular power switch now works,
so I don't have to use the Pin 11 power signal. The system seems to
dislike having he floppy, CD, and hard drive all hooked up at the same
time, so I'll just run it with the hard drive for now.
Thanks again for your help on this -- I learned about power supplies,
got the old computer working well enough, and had a successful morning