Help! ATX PC doesn't turn on

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Guest

Last week I was working with my ASUS A7V133 when it suddenly came to a
strange state: the front power light was blinking in the same way as if
it were sleeping. But nothing would make it alive, only this 4 sec press
on the power button would turn it off... and never on.

Now, when I turn the rear switch off for enough time (enough for the
mainboard led indicating power to turn off) and back on, if I press the
power button, the front light will be on for 1/10 sec and then off.
Nothing inside will move.

This is pretty annoying for it doesn't seem to be a power supply failure
(the mainboard seems to be powered), but who knows with these ATX boxes?

Can anybody give me a hint?

Thanks in advance,

David.
 
Last week I was working with my ASUS A7V133 when it suddenly came to a
strange state: the front power light was blinking in the same way as if
it were sleeping. But nothing would make it alive, only this 4 sec press
on the power button would turn it off... and never on.

Now, when I turn the rear switch off for enough time (enough for the
mainboard led indicating power to turn off) and back on, if I press the
power button, the front light will be on for 1/10 sec and then off.
Nothing inside will move.

This is pretty annoying for it doesn't seem to be a power supply failure
(the mainboard seems to be powered), but who knows with these ATX boxes?

Can anybody give me a hint?

Thanks in advance,

David.
Click to expand...

Open the system and examine the motherboard for swollen/leaky/vented
Capacitors, or residue under them, and of course anything else that
might be out of place, wrong, damaged, etc, while you're in there.

Has anything happend or been changed just prior to the onset of the
problem?

If you haver a voltage meter you might take voltage readings at the
motherboard power connector (while the system is "on") including at
least the +3, +5, and +12V lines. If proper voltage is preset you
might try turning off and unplug the system, unplugging the power
supply from the motherboard, then plug the power supply back into the
main ac, and finally short the power-on line to ground to see if the
power supply stays turned on. Leave only a hard drive connected to
the power supply at this point. So long as the power-on line is
shorted to ground the power supply should stay on, it's fan spinning
and the hard drive also spinning. Here's an aid to the pinout on the
ATX connector for the voltages to check and the power-on line:

http://216.71.121.115/usr_1034/atx_on.gif


Dave
 
David said:
Last week I was working with my ASUS A7V133 when it suddenly came to a
strange state: the front power light was blinking in the same way as if
it were sleeping. But nothing would make it alive, only this 4 sec press
on the power button would turn it off... and never on.
[...snip]

Can anybody give me a hint?
Click to expand...

First, disconnect everything from the power supply (including MB.) Plug
AC cord into the rear of the PS. IF the PS has its own rocker on/off
switch, turn it ON. There should be +5v on pin 9 of the 20 pin connector
(+5vsb, usually a violet wire.) There should be >0.8v on pin 14 (PS-ON,
usually a green wire.) This is from an internal pull-up to the +5vsb.

Connect PS power leads to 1 or 2 IDE HDs (for a load). Jumper pin 14
(PS-ON) to pin 13 (ground, black wire.) At this point, fan in PS should
start spinning, drives should spin, and + 5/12v, -5/12v, +3.3v, and
+5vsb should be present at 20 pin connector.

Disconnecting pin 14-13 jumper should turn supply back off.


When your system fails to start, what is the voltage on pin 9? If it is
less than 4.75v, either a) the logic on your motherboard is shorting
b) your +5vsb is under powered, or c) your PS is bad. It is
most likely a combination of b) and c).

If your +5vsb is OK, measure pin 14 of the PS/MB connector. If it is <0.8v
(and the +5vsb is OK), the power supply should be on. If pin 14 is <0.8v,
the +5vsb is OK, and the PS is OFF, the PS is bad. If pin 14 is >2.0v, the
power supply is being told to stay OFF by the MB. If depressing the front
panel ON/OFF switch does NOT lower pin 14 to <0.8v (and the +5vsb is OK),
then the problem is NOT the power supply, but rather MB related.
 
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