PSU : OR Motherboard ? Fan not spinning

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After 4 years of being on, my EM T2682
no longer powers on.

The symptoms ..

1. The original power fan spins, and the only sign
of life is the small LED for disk access when I press the large power

2. I ordered a replacement PSU .. This one is slightly different
  in that it has a POWER SWITCH ON THE REAR OF  PSU.


   AT ALL.


3. I'm thinking the FRONT POWER BUTTON via the motherboard controls
the PSU .. and starts the FAN to turn ?

In other words ..   I'm reluctant to order a new MB .. if the
replacement PSU is bad.

 Shouldn't the FAN spin on the new PSU when I plug it in
 and press the FRONT BUTTON ?

Re: PSU : OR Motherboard ? Fan not spinning

Yes there should be fans spinning as  you noted with the old power
supply, do note that some mobo's require an extra 4 pin plug, so check
thiis... not all power unit's have this plug. Something odd that the new
supply does not work.. I would check for this plug before asking for a

You could of course try it in a working computer or try a known good

The problem you described with the 'old' supply provides a reasonably
good clue, especially since it's 4 years old...  I would certainly be
looking at the bios back up battery, look's like a coin cell  and 4
years is about right I'd say for these to be replaced....

Removing this battery for more than about two minutes will result in
the bios setting to default.... but if the battery's duff it'll have
done just that - so you'll have to enter bios set up and set it up

... a duff battery will cause the fans to spin but will stop the bios
from booting up... so I'd say either power unit or bios battery first of
all before anything else.


Re: PSU : OR Motherboard ? Fan not spinning

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I'll try that in the morning.

Re: PSU : OR Motherboard ? Fan not spinning

Lost in the Wasteland wrote:
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The power switch on the back, turns the +5VSB output on. The +5VSB flows
to the motherboard, and powers chips like the Southbridge and the Super I/O

The power switch, on the front of the computer case, is wired to the PANEL
header. Usually the panel header is in the lower right hand corner of the
motherboard (but it is not forced to be there).

A "momentary" contact between the two power pins on the PANEL header, is
fed to the chips on the motherboard. They latch the signal, and make a
steady level out of that momentary contact. The steady level is used to
drive the PS_ON# pin on the 20 pin connector.

For reference, the pinout of a standard 20 pin power supply, is shown on
page 29 and 30 here:

To turn on the power supply manually, as a quick test, disconnect the
supply from the computer. Connecting PS_ON# (green wire) to an adjacent
COM (black wire) should be enough to cause the PSU fan to spin and power
up the supply. That tells you the supply is not dead.

It is a good idea to have a little bit of load on the supply, to help
it stay within regulation. Connecting a hard drive 1x4 Molex draws a little
current (but leave the data cable disconnected while doing that). If you
had a multimeter, you could use a paper clip in the PS_ON# and COM holes,
then use the multimeter to probe the other pins on the main connector, and
measure the voltages.

In the above, my assumption is that the Emachine T2682 is a standard ATX.
I get that impression from the lists of substitute supplies for it, but
haven't checked any Emachines documents yet. Verify that the wire harness
colors, match the colors suggested in the ATX spec.

At least with some of these prebuilt computers in the past, the idea was,
the power supply blows, and it takes out the motherboard at the same
time. Either with the new supply, you forgot to connect something, or
the motherboard is blown. You could try forcing the supply on, by
connecting PS_ON# to COM while everything is cabled up, but there are
some safety issues with doing that. Specifically, if the motherboard
has any self-protection mechanisms, they would be defeated by
connecting PS_ON# to COM, while the PSU was fully cabled up to the
motherboard. At the very least, your motherboard probably has a
working THERMTRIP, and if the processor overheats, THERMTRIP would
attempt to turn the power off. Forcing PS_ON# to COM would prevent
THERMTRIP from working. So that is the slight disadvantage of using
PS_ON# when everything is connected - if the processor heatsink
fell off, the computer could not protect itself against overheat.
But if you otherwise have nothing to lose, you can try connecting
PS_ON# to COM, while everything is connected in a normal fashion.

If you have another computer, at the very least, make a backup copy
of the files on your hard drive. Or, alternately, start your testing
with the hard drive fully disconnected. That may protect it from any
problems the system currently has, at least until you can see a BIOS
screen and know that good things are happening. But having a backup
in hand is probably the single most important thing, before you go
any further.

Your motherboard - Imperial_GV (Intel 865GV based, no AGP video slot)


Re: PSU : OR Motherboard ? Fan not spinning

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There you go.
 Shunting that to gnd does indeed cause
 the PSU to wake up and fan to turn .. but I get no sign of life.

  That was a good idea to try.
 I guess that pretty much diagnoses the MB.

Geez .. I've learned alot about ATX PC's now ..

I always suspected PC's were pretty much cookie-cutter
clones .. Dell, HP, Emachine, Acme, ... They are really
all the same when it comes down to the basics.

Which gets my mind wandering .. should I get a
direct replacement MB or upgrade to a faster AMD style
compatible ATX MB !

Thanks for the help Paul and Dave !

Re: PSU : OR Motherboard ? Fan not spinning

Lost in the Wasteland wrote:
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One web site listed an exact replacement motherboard for
a fairly high price. So that may be an issue, if you
don't want to sink a lot of money into the system.
I cannot keep track of which prebuilt computers have
their install software disks keyed to the motherboard or
the hard drive, which is another thing to consider. Getting
a separate copy of WinXP and finding an ATX style motherboard
that will fit within the box, is a possible solution. If you
change motherboards, chances are you'd need to do a repair
install, and will need some kind of Windows install CD to
do it.

Maybe someone else knows the details of whether the software
that comes with your computer, will play nice with another
brand/type of motherboard.


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