Puzzling ATX to AT power supply converter

  • Thread starter Thread starter Johan Ericsson
  • Start date Start date
J

Johan Ericsson

Hallo,

I recently acquired a cable which apparently should make it possible
to use an ATX power supply in an older AT-case. However, I am not
quite sure of how to install it since in addition to the expected
standard AT and ATX connectors there is also a 3-pin connector which
looks somewhat like a smaller version of a floppy power supply plug. I
guess it should have something to do with the power on/off button but
I don't really see how it could be fitted.
Does anyone have any idea what it could be used for?

Thanks.

//Regards, Johan
 
Johan said:
I recently acquired a cable which apparently should make it possible
to use an ATX power supply in an older AT-case. However, I am not
quite sure of how to install it since in addition to the expected
standard AT and ATX connectors there is also a 3-pin connector which
looks somewhat like a smaller version of a floppy power supply plug. I
guess it should have something to do with the power on/off button but
I don't really see how it could be fitted.
Does anyone have any idea what it could be used for?
Click to expand...

It doesn't look like

http://www.pcpowercooling.com/products/alarmandaccesories/accessories/popups/indexatxtoatcable.htm

What color are the wires, and where do they come from?
 
I see now that we are talking about an adaptor. I misread and thought you
were pseaking of a lead coming from an ATX power supply and you didn't know
how to connect it to you ATX/AT adaptor.

Whoops!




Perhaps it's a power supply cooling fan trigger wire? I have two power
 
Johan said:
No, it doesn't. The long wires on that one appear to connect to the
old AT power switch quite nicely.

The wires are colored brown, gray and black. They appear to be
connected to ground, PS_ON and +5vdc (standby voltage) so it seems
that the connector has something to do with the activation of the
power supply.

Here is a complete sketch of the wiring, as seen from the end of the
connectors where the cables emerge:
http://www.algonet.se/~warnut/atxtoat.jpg
Click to expand...

Whew! I don't know. It looks like some sort of turn on circuit using the
+5vsb as a pull up (not needed since pin 14 has internal pull up), or the
+5vsb is the Vcc in some sort of proprietary circuit. I vote for the
latter.

Get the PCP&C device, or build your own interface to the on/off switch.
 
I have seen these also. There were two different models of converter. They
came with early ATX cases so you could put a regular AT motherboard in them.
I saved the converters and found they were power supply/case specific
later.

One was just a converter with no extra wires, I think the manual ATX power
switch on the back turned on the power to the AT motherboard. Don't ask me
how.

On the other, it had extra leads and connected to the ATC momentary on
contact switch.

Basically useless without the case but you know how you can hoard leftover
parts...
 
Here is a complete sketch of the wiring, as seen from the end
of the connectors where the cables emerge:
http://www.algonet.se/~warnut/atxtoat.jpg
Click to expand...

Your diagram shows that the top pin of the "unknown" connector goes to
ground (black wire on ATX), the middle one goes to Power_On (green
wire), and the bottom to +5V_standby (purple wire). To turn on the
ATX power supply, connect that Power_On pin to ground, but if you're
uncomfortable about possibly causing damage with a direct short, make
the connection with a 200-500 ohm resistor (Radio Shack). The
Power_On and ground pins can be wired to the 2 lugs on one side of an
AT power switch (either left or right lugs when looking at the switch
from the front), but don't have any other wires connected to the
switch. The +5V_standby can be wired to an approximately 300 ohm
resistor in series with an LED, the other lead of the LED to the
Power_On wire. The LED will then glow when the power switch is turned
on, unless the LED leads are reversed.
 
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