modern switching power supply faults
Curtis H. Wilbar Jr.
rescue at hawkmountain.net
Sat Apr 12 23:56:47 CDT 2008
I have two Dell switchers out of P4 based 1U servers.
The first one has a failure in the startup circuit... pressing the power
lead to a flash of the power light... and that's it.
The second one failed spectacularly....
There is a wire wound power resistor (5W15RJ) near the AC input... it
and I do mean cooked. It came out in pieces (with almost no effort),
nearby capacitor and a nearby relay. It also did a pretty good job of
the PCB (but not bad enough it could not be used).
I suspected maybe shorted primary full wave rectifier... but I used the
diode test and got what I'd expect.
Oddly, despite there being a fuse on the primary side... it's still
good... it wasn't
That resistor got hot hot hot. Could that resistor have failed on it's
I suspect something further down the circuit must have a problem.
I'd be happy if I could make one power supply out of the two. These are not
simple supplies however. While much of the switching transistors,
bridge rectifiers, capacitors and the usual fair in a switcher are
identified, there is a 6" x 1" "brain" board (I'll call it that as it
pots, the ps fan circuit, quite a # of surface mount components on both
it, and it interfaces with the main PCB with 34 connections.
These are Dell W5916 supplies. Unsure who really makes these for Dell, only
other marking is Model: HP-U280EF3. Both these supplies had been cycled 4
times on/off the mains due to a power failure (power fail, generator
power restored, generator cycled off, repeat process one more time) within a
few minutes of each other. The first one was dead immediately after
one that has a problem in the start circuit (or a monitor/etc is
shutting it down
when it detects a problem during turn on). The second one failed almost two
I know this isn't particularly classic... but I know that there are
those out there
much wiser than me in switchmode power supplies. So lets pretend it is
2014 that way the supplies will be 10 years old :-)....
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