modern switching power supply faults
dkelvey at hotmail.com
Sun Apr 13 09:16:31 CDT 2008
> Date: Sun, 13 Apr 2008 00:56:47 -0400
> From: rescue at hawkmountain.net
> To: cctalk at classiccmp.org
> Subject: modern switching power supply faults
> I have two Dell switchers out of P4 based 1U servers.
> The first one has a failure in the startup circuit... pressing the power
> button will
> lead to a flash of the power light... and that's it.
> The second one failed spectacularly....
I to have a problem with one.
It is similar to your first one.
Basically, the first problem is that something is failing to start
the switcher feedback. What happens on powerup is that it is
given one kick. This gets the 12v going to the regulator circuit.
It is then suppose to send pulses through the pulse transformer
to fire the switching transistors.
It could be most anything in the regulation loop. I fixed one in
the past when I found an open wire in the pulse transformer.
Still, it could have been anything in the feedback path, including
regulator ICs, filter caps, diodes, resistors, etc.
Mine is failing on a load related problem. As I connect more
load, it fails to powerup. It is funny that it seem to be more sensitive
to the loads that use the 12V. It seems to run the 5V loads fine.
Your second one has most likely had a failed switching transformer
and switching transistor. There could also be a load issue, such as
shorted rectifier diodes on the secondary but that is unlikely. This
would tend to keep the 12V from coming up and you'd get no
pulses to fire the switching transistors. They're unlikely to fail if not turned on.
More immediate than e-mail? Get instant access with Windows Live Messenger.
More information about the cctech