Hi,
I recently replaced my desktop's PSU with an older Ultra ult-vx700 I had
in storage.ÿ At first everything seemed ok, but then a couple of days
ago, I noticed that the fan would intermittently stop and then restart.
I checked what details I could find on the PSU and there is no "eco"
mode, nor is there any setting for such in my BIOS.ÿ Since I primarily
use the latest version of Ubuntu for my OS, I thought perhaps an update might have triggered some sort of power saving mode, but doesn't seem
likely since the fan still does this while starting up before entering
the OS.
Today, I replaced the fan with a known good one I had as a spare.ÿ Same behavior, so beginning to suspect something with the PSU.ÿ Thoughts and comments welcome and thank you in advance.
Nick
On 15/04/2026 16:33, Nick Sebul wrote:
Hi,
I recently replaced my desktop's PSU with an older Ultra ult-vx700 I
had in storage.ÿ At first everything seemed ok, but then a couple of
days ago, I noticed that the fan would intermittently stop and then
restart. I checked what details I could find on the PSU and there is
no "eco" mode, nor is there any setting for such in my BIOS.ÿ Since I
primarily use the latest version of Ubuntu for my OS, I thought
perhaps an update might have triggered some sort of power saving mode,
but doesn't seem likely since the fan still does this while starting
up before entering the OS.
Today, I replaced the fan with a known good one I had as a spare.
Same behavior, so beginning to suspect something with the PSU.
Thoughts and comments welcome and thank you in advance.
Nick
I can hear my fan start up when I use a lot of CPU, but it stops when I
stop using that particular program. Probably does the same if I open too
may tabs. I just thought that was normal.
On 15/04/2026 16:33, Nick Sebul wrote:
Hi,
I recently replaced my desktop's PSU with an older Ultra ult-vx700 I had in storage.ÿ At first everything seemed ok, but then a couple of days ago, I noticed that the fan would intermittently stop and then restart. I checked what details I could find on the PSU and there is no "eco" mode, nor is there any setting for such in my BIOS.ÿ Since I primarily use the latest version of Ubuntu for my OS, I thought perhaps an update might have triggered some sort of power saving mode, but doesn't seem likely since the fan still does this while starting up before entering the OS.
Today, I replaced the fan with a known good one I had as a spare.ÿ Same behavior, so beginning to suspect something with the PSU.ÿ Thoughts and comments welcome and thank you in advance.
Nick
I can hear my fan start up when I use a lot of CPU, but it stops when I stop using that particular program. Probably does the same if I open too may tabs. I just thought that was normal.
On Wed, 4/15/2026 12:06 PM, Jim the Geordie wrote:
On 15/04/2026 16:33, Nick Sebul wrote:
Hi,
I recently replaced my desktop's PSU with an older Ultra ult-vx700 I had in storage.ÿ At first everything seemed ok, but then a couple of days ago, I noticed that the fan would intermittently stop and then restart. I checked what details I could find on the PSU and there is no "eco" mode, nor is there any setting for such in my BIOS.ÿ Since I primarily use the latest version of Ubuntu for my OS, I thought perhaps an update might have triggered some sort of power saving mode, but doesn't seem likely since the fan still does this while starting up before entering the OS.
Today, I replaced the fan with a known good one I had as a spare.ÿ Same behavior, so beginning to suspect something with the PSU.ÿ Thoughts and comments welcome and thank you in advance.
Nick
I can hear my fan start up when I use a lot of CPU, but it stops when I stop using that particular program. Probably does the same if I open too may tabs. I just thought that was normal.
When Intel "invented" PWM fans, by writing a spec for it,
the intention was, at zero control input, the fan was
supposed to spin at MIN, not at ZERO. Having fans that
stop spinning (one way or another), confuses and concerns
users, as they cannot be sure what is going on.
This is an Ultra brand ATX, a company consisting of four guys in
Cali, who contracted the manufacturing to others. In their
support forum, they used to "berate" users who reported
valid concerns with the products. I don't know if they're
still in business or not. I also cannot tell you who makes
their PSUs (since they didn't have their own factory in Cali).
Lots of other companies have used this model (PCPC),
and they had a much better reputation for knowing their
stuff, even though they were not personally making the items.
*******
For that particular model, someone had a situation where
the fan speed went up for no reason.
https://www.overclock.net/threads/psu-fan-speeds.410102/
There was one build with a failure to start, which isn't
conclusive of anything.
The era might be the year 2007 ??? The fan should be running
off the +12V rail, which is 12V @ 40A or so. Via current
limiters, that would be split, so 20A or so would go to
the CPU, and 20A would go to the 24 pin connector. At a guess.
https://en.wikipedia.org/wiki/Capacitor_plague
It's hard to say what kind of circuit feeds the fan speed.
There's no processor inside most ATX power supplies, so
an analog circuit controls the fan speed. On the PC itself,
the SuperI/O has some automation for adjusting the fan speed,
but that's not always "clever enough" for the job, so the
BIOS calls via SMI, could include an opportunity for adjustment.
The PSU is a lot dumber, and should react to a temperature
measured somewhere.
*******
OK, I have a theory. The circuit uses an electrolytic cap,
the cap is leaking, and the cap is behaving as much as a
resistor as it is a capacitor.
You can undo the four screws that hold the ATX top sheet metal
U-plate cover. You don't need to touch any wiring or
components inside. Just look at the tops of the caps for
brown deposits (leaking at the vent on top). The Capacitor Plague
article has pictures of the brown stuff. The vent
is there for emergency pressure release (to avoid an
explosion as the release mechanism).
I had an Antec, a ChannelWell OEM, where the four +5V output
caps were leaking. And the PSU, when the machine was cold,
a puff of gray smoke used to come out of the PSU vent.
That tells you that failure due to leaking caps is imminent.
A second Antec, it had some sort of defect, but there
were no visual indicators at all of what the problem was
with it. The problem would be somewhere around the
dual transistors that switch the primary side of the transformer.
But nothing was burned or discolored. And that was a long
time ago now.
Paul
I haven't checked the caps yet, but I am going to at some point.ÿ I am beginning to wonder though if this isn't some sort of normal behavior for this PSU.ÿ When the room temps were cooler, both of its fans ran continuously at a slow speed.ÿ It has only been since the temps have approached or went above 70 F in here that this behavior started.
I also checked the fan at the rear of the PSU as this is a dual fan unit.ÿ Both stop.ÿ Then, once a few seconds go by, both start up again.
The only difference with the PSU behavior is that now, when the fans start, they are spinning at a faster rate but not continuously and then go off.ÿ The behavior when the room was cooler was continuous fans running at a slow speed (but, to be honest, maybe they weren't running at all and I thought they were running slowly).
My understanding was that this PSU was intended for lower end gaming systems.ÿ As such, I never owned anything like it, only standard supplies (basically whatever came with the PC).ÿ So, this behavior I'm thinking is odd might be normal.
I guess I'll know for sure once the cool snap arrives and the room drops back into the low 60's/ upper 50's.ÿ If the behavior ceases, then I'll pretty much know its how its designed.
On Thu, 4/16/2026 11:56 AM, Nick Sebul wrote:
I haven't checked the caps yet, but I am going to at some point.ÿ I am beginning to wonder though if this isn't some sort of normal behavior for this PSU.ÿ When the room temps were cooler, both of its fans ran continuously at a slow speed.ÿ It has only been since the temps have approached or went above 70 F in here that this behavior started.
I also checked the fan at the rear of the PSU as this is a dual fan unit.ÿ Both stop.ÿ Then, once a few seconds go by, both start up again.
The only difference with the PSU behavior is that now, when the fans start, they are spinning at a faster rate but not continuously and then go off.ÿ The behavior when the room was cooler was continuous fans running at a slow speed (but, to be honest, maybe they weren't running at all and I thought they were running slowly).
My understanding was that this PSU was intended for lower end gaming systems.ÿ As such, I never owned anything like it, only standard supplies (basically whatever came with the PC).ÿ So, this behavior I'm thinking is odd might be normal.
I guess I'll know for sure once the cool snap arrives and the room drops back into the low 60's/ upper 50's.ÿ If the behavior ceases, then I'll pretty much know its how its designed.
Does your case have enough intake-fans, to pressurize the case
and cause some air to blow through the PSU anyway ?
That's one way to provide air to a PSU, if it won't
do the job itself. Not a particularly good way,
but it's better than nothing.
While in theory, you can fit your own fan
to the exterior of the PSU, there isn't always room
or mount points, to do it that way.
Paul
for this PSU. When the room temps were cooler, both of its fans ran continuously at a slow speed. It has only been since the temps have approached or went above 70 F in here that this behavior started.
I also checked the fan at the rear of the PSU as this is a dual fan
unit. Both stop. Then, once a few seconds go by, both start up again.
The only difference with the PSU behavior is that now, when the fans
start, they are spinning at a faster rate but not continuously and then
go off. The behavior when the room was cooler was continuous fans
running at a slow speed (but, to be honest, maybe they weren't running
at all and I thought they were running slowly).
My understanding was that this PSU was intended for lower end gaming systems. As such, I never owned anything like it, only standard
supplies (basically whatever came with the PC). So, this behavior I'm thinking is odd might be normal.
I guess I'll know for sure once the cool snap arrives and the room drops back into the low 60's/ upper 50's. If the behavior ceases, then I'll pretty much know its how its designed.
I think it might be time for a different PSU.
On 2026/4/16 16:56:57, Nick Sebul wrote:
[]
for this PSU. When the room temps were cooler, both of its fans ran
continuously at a slow speed. It has only been since the temps have
approached or went above 70 F in here that this behavior started.
I also checked the fan at the rear of the PSU as this is a dual fan
unit. Both stop. Then, once a few seconds go by, both start up again.
The only difference with the PSU behavior is that now, when the fans
start, they are spinning at a faster rate but not continuously and then
go off. The behavior when the room was cooler was continuous fans
running at a slow speed (but, to be honest, maybe they weren't running
at all and I thought they were running slowly).
My understanding was that this PSU was intended for lower end gaming
systems. As such, I never owned anything like it, only standard
supplies (basically whatever came with the PC). So, this behavior I'm
thinking is odd might be normal.
I guess I'll know for sure once the cool snap arrives and the room drops
back into the low 60's/ upper 50's. If the behavior ceases, then I'll
pretty much know its how its designed.
Could you turn up the A/C - or, put a desk fan on the PC - to see?
A puff of grey smoke at power up, is
another sign of impending failure -- if you see
grey smoke, the supply will die in around seven days
or so.
Paul
Paul wrote on 4/16/2026 4:22 PM:
A puff of grey smoke at power up, is
another sign of impending failure -- if you see
grey smoke, the supply will die in around seven days
or so.
ÿÿÿ Paul
What if the smoke is green?ÿ Is there a way to calculate when the power supply will die?
I think you'd get less than seven days if the smoke isn't grey.
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