[Gllug] Mysterious reboot

[Peter Grandi]

>>> On Thu, 17 Nov 2005 17:56:25 -0000, "Wiehe, Simon"
>>> <simon.wiehe at csfb.com> said:

simon.wiehe> Hi, I got home from work today to find that my
simon.wiehe> machine had mysteriously restarted. [ ... ]

simon.wiehe> [ ... ] surely if there was a failure I would not
simon.wiehe> get restarting in the log.

Note necessarily...

simon.wiehe> I thought about power and we had no power problems
simon.wiehe> at that time,

Bah, guessing wildly, most likely it is power -- a 2-3 second
dip in voltage can make the system reboot itself; a full
interruption in the supply is not required. Most short brownouts
are smoothed over the by the PSU, so they have been happening
without anybody noticing.

simon.wiehe> the only other thing I can think of is the
simon.wiehe> temperature, it was running at 45 degrees, normally
simon.wiehe> idles at about 47-49 degrees, [ ... ]

Guessing wildly, unlikely -- usually recent and not so recent
PCs have temperature related shutdown. Overheating might cause
a crash and reboot, but on my experience brownouts is more
likely.

simon.wiehe> [ ... ] Can someone help me to where to look to
simon.wiehe> investigate further? [ ... ]

Well sometimes it is just hard to even suggest where to look.

Short brownouts are not unknown, and from you say so far there
does not seem any reason to worry overly about whatever has
happened. Getting a £100 UPS might be a good idea in general.

But on reflection you say that the PC has been always on (like
mine) for quite a while:

  simon.wiehe> It is normally up for weeks or months without the
  simon.wiehe> need to restart and over the last 4 years I have
  simon.wiehe> never had this happen,

My impression is low cost PCs (and even not so low cost ones)
tend to go flakey well before 4 years (usually after at most 2
years one really has to start replacing bits and pieces).

  Today I just helped diagnose some funny startup behaviour for
  a friend's PC; it turned out that after not quite two years
  his power supply had started to give, and would only manage
  4.75V on the 5V line, and this with almost nothing connected,
  which led to rather erratic behaviour (e.g. detecting 231MB of
  RAM :->).

As to things that might have started going flakey:

* First, I would check _all_ fans in the machine, to make sure
  they have not gummed up or rattle too much. Some fairly cheeky
  manufacturers put sleeve bearing fans on motherboard chips,
  and these gum up pretty quickly, and this can cause damage.
  Some use poor quality ball bearing fans, which wear out well
  before 4 years.

  At least for most ball bearing fans wear out means lots of
  rattle, rather than seizing up like for sleeve bearing; but
  then it is easy to relubricate sleeve bearings, but ball
  bearing fans have to be replaced.

* Second, I would also check the output voltages on one of the
  molex connectors: the two inner sockets are neutral, and the
  two outer ones should deliver pretty close to 5V and 12V
  relative to that; usually the 12V is not a problem, if the
  PSU is going the 5V is more likely to start sagging.

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