Greg Magnusson said:
I'm building two PCs with the same exact hardware, using pretested
mobo/cpu/ram bundles (the mobo is an Asus A8V). The issue is, the PC
powers up when the power supply master switch is turned on (not the
front panel power switch), which I believe isn't supposed to happen.
I've tried both mobos and the problem persists with both. Even with
no jumpers connected to the case, the PC powers on. It's an Antec
case with a Smartpower 350 watt power supply.
I'm assuming the issue is a silly error on my part, but would anyone
know where to look first?
The only time that happened to me, an IDE ribbon cable was only
half inserted into its connector. The computer would start as soon
as the power switch on the back was turned on. Generally, anything
which is stressing the Southbridge, can screw up the power switch
conditioning logic that drives the PS_ON# signal to the PSU. I was
lucky, in that my mobo survived the incident.
I would do a "cardboard test". Remove PSU and motherboard from the
case and assemble them on your table top. Place something thick
like a phone book underneath the motherboard, to lift it above the
table, and to give some support. By lifting it above table level,
that leaves room for the underhang of the PCI or AGP cards you will
eventually be installing. On my last two system builds, I completely
assembled and tested the computer, before even getting close
to the computer case. A tabletop build leaves plenty of room to
see what you are doing.
See if the symptoms are the same with the motherboard stripped
down, just it and the PSU. Make sure everything is disconnected
from the PANEL header. You can use a screwdriver tip, to short
together the two pins where normally you would have the power
switch connected. Only a momentary contact is needed to cause
the motherboard to switch on.
I believe your motherboard has "Vocal POST". Connect amplified
speakers to the green Lineout connector on the back of the
computer. Make sure your screwdriver tip has the static charge
drained off it, before momentarily touching the tip, to the
two power switch pins on the PANEL header. The response should
be, the PSU fan starts to spin, the Northbridge fan spins, and
the Vocal POST tells you that no CPU is present.
Always turn off and unplug the computer between tests. Never
insert or remove components with the power supply connected to
the wall (this is a conservative practice, intended to prevent
the accidental application of +5VSB).
You can then add components one at a time, and test after each
one. Add CPU, memory, video card + monitor, keyboard + mouse,
and eventually you should get it to the point that it is looking
for a drive to boot from. By listening to the Vocal POST, you
will be able to tell, that the component you just added, is being
recognized.
There is more crap I could write, but at least see if you can
get further than you are currently, by starting with the most
minimal system possible - just mobo and PSU.
When table top testing, always be aware that the AGP and PCI
cards, are not supported properly. Before plugging in the PSU,
always check that the AGP/PCI cards are fully seated in their
sockets, and try to remove any possible cable stress that could
pull a card out of its socket while the computer is running.
Paul
