Computer Hardware AT/ATX PS question

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Subject Author Date
AT/ATX PS question Pelysma 07-10-05
---> Re: AT/ATX PS question Floyd L. Davids...07-10-05
Posted by ric on July 12, 2005, 12:32 pm
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VWWall wrote:

> Floyd L. Davidson wrote:
> >
> >>You did *say*: "causes the AC to be remotely switched...".
> >>The AC is already on, which provides the +5 VSB. The grounding
> >>of the green wire just turns on the DC switch circuit. Holding
> >
> >
> > "The DC switch circuit"??
>
> The pulse width modulator to the DC switching transistors. That's why
> they're called "switching power supplies".
> >
> >
> >> in the front panel switch causes the MB logic to remove the
> >>ground and turn off he ATX power supply.
> >
> >
> > I think you're trying a little too hard on that one.
>
> Not hard at all--that's how it works! :-)
>
> --
> VWW

Note to VWW: I have put Floyd in my "Don't wrestle with pigs" file.
[You just get dirty and the pig enjoys it.] No matter what he said
incorrectly, his response will be "That's what I said. You're trying
too hard on this one."


Posted by VWWall on July 12, 2005, 7:54 pm
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ric wrote:

> Note to VWW: I have put Floyd in my "Don't wrestle with pigs" file.
> [You just get dirty and the pig enjoys it.] No matter what he said
> incorrectly, his response will be "That's what I said. You're trying
> too hard on this one."

I found that out in alt.engineering.electrical, where he's constantly
doing the same. :-(

He must have a boring job in Alaska!

--
Virg Wall, P.E. ,K6EVE


Posted by Pelysma on July 14, 2005, 3:03 am
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> I think he would
> get through the confusion.
>
Thanks for the vote of confidence.
;-)

BTW, I do understand all about these switches. I only wanted to know if I
needed to change a jumper on the motherboard before unplugging the AT PSU
and plugging in the ATX one! That's moot now, except for the pure academic
exercise of learning something new.

As I've come to expect, Kony gave the best information.

--
P.




Posted by Pelysma on July 11, 2005, 3:46 pm
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>>"Floyd L. Davidson" wrote:
>>
>>> With an ATX supply, no such AC cord exists, and instead the
>>> green wire on the connector (routed through pins on the
>>> motherboard) is switched to ground by the front panel ON/OFF
>>> switch, and that causes the AC to be remotely switched inside
>>> the power supply.
>>
>>Not quite accurate.
>
> You've just repeated the same thing I said with more (and
> unnecessary) detail. How is it not accurate?
>
>>The PS_ON (green) wire goes to a logic circuit
>>on the MB. The on/off switch goes to this circuit as well. Engaging
>>the momentary on/off switch toggles the output of this logic circuit,
>>changing its state, and turning the PSU either on or off. (If the
>>logic output toggled low, the PSU turns on. If the logic output
>>toggled high, the PSU turns off.)
>
> That's correct detail, but it doesn't add anything at all to
> understanding the point about the switch.
>
>>Beside, the OP said he was going to use the RESET switch for his
>>on/off switch. That will work just fine.
>
> It will work. Of course then he doesn't have a RESET switch,
> only an ON/OFF switch that is mislabeled, and an ON/OFF switch
> that is labeled but doesn't work... which is a nice recipe for
> confusion.
>

or a nice job for a sharpie.

> Seems to me that finding another AT power supply is a *much*
> better idea. Or just switching the whole thing to an ATX case.
>
or what I did, which is to replace the two damaged Molex connectors on the
AT PSU so I can install two more drives. It probably won't do what I
wanted to do with the extra drives, anyway. I do still need to transfer
something like 400 MB of images from it to a CD, and plan to keep it running
so I can use Access for a little while for another project, but it was given
to me to scrap and scrap it soon shall be.

The two pins that should have been the power-on header in the diagram are
missing from this board, so I'm not going to get anywhere with the ATX idea.

Thanks, both, for your input.

--
P.




Posted by Pelysma on July 11, 2005, 2:05 am
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>>
>>Is there anything I need to know, or anything I need to reconfigure,
>>before
>>unplugging the AT PSU and plugging in the ATX one?
>
> How is the front panel ON/OFF power switch wired?
>
> With an AT supply there will be a (probably black) AC cord coming
> out of the supply going to the ON/OFF switch. That cord carries
> 120VAC, and it is switched at the front panel.
>
> With an ATX supply, no such AC cord exists, and instead the
> green wire on the connector (routed through pins on the
> motherboard) is switched to ground by the front panel ON/OFF
> switch, and that causes the AC to be remotely switched inside
> the power supply.
>
> Very different arrangements, which have more to do with the case
> and the power supply than with the motherboard. Your
> motherboard was apparently designed to work with either. Which
> probably means you could switch it to an ATX case. But swapping
> the AT supply in an AT case to an ATX supply isn't that easy.
>
> --
> Floyd L. Davidson <http://web.newsguy.com/floyd_davidson>
> Ukpeagvik (Barrow, Alaska) floyd@barrow.com

Well, they both physically fit. I know about the AC cord to the front; I
also know that the power switch on the front of an ATX case is identical to
the reset switch on both, a momentary spst pushbutton in series with a small
resistor. In most ATX boards there is a pair of pins labeled RST for the
reset switch, and a pair labeled SOFT PWR for the power switch. I've
located the RST pins and the wire connected to them.

Usually if the pins aren't labeled I go in there, determine some likely
candidates, and briefly short each likely pair with a tool I made, a
1000-ohm resistor plugged into a little red jumper-style connector and
epoxied to a popsicle stick. (I used to use a Phillips screwdriver, but had
second thoughts about shorting the wrong thing without resistance.)

The pair that starts the computer gets the wire from what was the reset
switch.

So far on this board I haven't found a pair that starts the machine. But
there are some jumpers around the switch headers and around the power
connectors that I can't identify, and I don't have TFM for the board at the
moment.

Anyway, thanks for your input.

--
P.




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