[PLUG] computer will not start (2X)

[King Beowulf]

On 07/18/2014 12:37 PM, Denis Heidtmann wrote:
> Narrowed down to a problem with the standby 5V.  The MB has an LED
> which indicates that the standby 5 volt supply is on.  This LED
> flashes when the problem occurs, indicating overcurrent, shutdown,
> repeat.  The two times this has occurred it went away spontaneously
> (Nothing I was doing can be said to be the cause for the problem going
> away.)  I watched the LED while unplugging back cables (keyboard,
> mouse, USB, etc) one at a time.  Nothing changed the status.  Then
> while doing nothing it suddenly changed--the LED became steady on.
> Then the thing started fine.
> 
> The computer is often completely powered off--no AC to the power cord.
> Other times it is off with AC on.  On the 2nd occurrence it was in the
> latter state when I attempted to start it.
> 
> The PS is a 380 watt Antec.
> 
> I am open to suggestions on how to diagnose this problem.  My first
> though is to measure the standby 5V to see if it is marginal.  I have
> to see where is the safest place to put a probe.
> 
> -Denis

What's the history of that Power Supply (PS)? Age? Stuck straight into
the wall? UL 1449 surge power strip? UPS? Any good Lightning Storms or
power failures over the years?

How many doodads are plugged into your system that uses 5V? All USB
devices do. CPU fan is 12V but some case fans run on 5V. DVD/CD/hard
drives use both 5V and 12V.  PS wattage is not as important as the
current (in amps) the 5V and 12V rails can support. The biggest current
draw is when you are firing it all up. Perhaps the PS just can't push
rated current anymore. You can monitor the voltage off of an unused PS
connector when you power up and run.

I would swap out for a known good power supply before poking at the
motherboard.

Once you verify the PS, you can check for bad capacitors or on the
motherboard.  But if the mobo is flaky, not much for it but to get a new
one.

Have fun!
Ed