M789 power loss restart

Joshua Wise joshua at joshuawise.com
Sun Oct 17 13:54:00 CEST 2004

> Previously with 787cl+ motherboard it helped to short-circuit the 14th
> and  the  15th  pins  of  the ATX connector so the PSU stayed on. With
> M789CLU  such  a  trick  does  not  work. The PSU stays on, but the MB
> doesn't boot.
> Does anybody know how can I make the board to be always on?
> Is there any port register that I should write to?
> Or is it a CMOS bit?
Not sure if there's a software solution, but the hardware solution I'd
recommend would be a 555 timer or some such. Connect the output to a
transistor that would short the power switch lines, and have it pulse
every 30sec or so. (29sec off, 1sec on, or thereabouts) That would give
the board enough time to get into protected mode (and hence refuse to
power down at a single toggle of the switch), while still having a
vaguely responsive system after poweron. You would have to disable acpid
in Linux to keep it from powering itself down again, but that is not a
big deal.

My schematic would look something like this:

    ^ +5V
    |   |   |           |
+--O---O---O---O--+    |
|  +  DSC THR BYP |    |
  )      555       |    |
| GND TRG OUT RST |    |
+--O---O---O---O--+    |
    |   |   |           |
   GND  +---)-----------+
SW+ ----\  |
          |-+   (NPN)
SW- ----/


Message not GPG signed because it would screw with the ASCII art; sorry. 
If you would like me to resend with a GPG signature I would be more than 
happy to do so.

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