OT: Weird Hardware Problem

Valeri Galtsev galtsev at kicp.uchicago.edu
Wed May 20 16:07:41 UTC 2020

On 5/20/20 10:50 AM, Tim Daneliuk wrote:
> On 5/19/20 8:46 AM, Tim Daneliuk wrote:
>> I was recently given a Dell Inspiron 3847 which has an i7-4790 and 16G
>> of memory.  Perfect for multibooting BSD and Linux.  It needed a new power
>> supply but now that this is installed, it's exhibiting a very strange
>> problem.
>> The machine will work for hours flawless and then - for no apparent reason -
>> reboot randomly.  The former owner reports that this was also happening
>> when they last had it running Win8.
> All signs point to an inadequate power supply.
> When I initially got the machine, I had to replace the onboard
> supply because the fan bearings on it were bad and loud.  The former
> owner reported that the machine had - in fact - been experiencing
> random reboots of late.
> I replaced the old supply with a "good" used  500W ATX supply and
> the reboot problem was still noted as above.
> This morning, I pulled the used supply and put the only new PS I have
> in stock - at 350W ATX unit - and tried to recreate the problem I'd
> been able to force consistently before during Linux install.  Voila!
> It worked.
> Now I need to monitor this thing for the next day or so to ensure that
> the problem is - indeed gone.
> Interesting that a new 350W supply does the trick when an apparently working
> 500W didn't.  As someone pointed out, this could well be old electrolytics
> not holding the rail voltage well under stress.

Yes, it was I who mentioned electrolytic capacitors. And that goes about 
both PS and system board (the last mostly the ones situated around CPU). 
The trouble is: not filtering well enough ripple on the power leads of 
Second problem (electronically related) would be: older components, 
mostly hard drives, start consume more power with age, i.e. higher 
current, thus increasing the level of ripple as ripple is mostly the 
voltage change after capacitor gives out some charge
Dell is known to build workstations without much reserve on PS capacity 
(I have a feeling I told this already on this thread). Which means, 
older Dell workstations are more likely to be pushed to the "just 
marginally not powerful enough" power supply. Especially as parts inside 
PS age as well. And capacitors are more likely to leak electrolyte thus 
loosing capacitance if they are overheated. Instability with age will be 
more likely in machines with large number of mechanical hard drives, so 
storage servers build with PS of just right power are more likely to 
become "unstable".

Bottom line: measure what your machine consumes, and give it PS twice as 
powerful as its maximum consumption under stress load.

I'm happy you solved it!


> ----------------------------------------------------------------------------
> Tim Daneliuk     tundra at tundraware.com
> PGP Key:         http://www.tundraware.com/PGP/
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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247

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