[PLUG] SON OF spontaneous reboots

[Keith Lofstrom]

Remember Kevin Cosgrove's message of Sat, 22 May 2004?
> For the last 3-4 days my machine is rebooting on its own.  It shuts
> down at 6:32-ish and is back up at 6:43-ish.


This has been happening to me for the last 3 days.   My server is on a
UPS;  it has been going down (to the beep of the UPS), and coming back
up around 6:16:11 AM, same time within a second for 3 days running.
Remarkably precise.

Nothing scheduled in cron at that time (I thought, read on) so I said
"bad UPS".  I took the machine down and restarted, stopping on the
GRUB splash screen.  Unplugged the UPS feed, the power went out.  Bad
UPS.  Opened the UPS and probed the two 12V, 17AH batteries in
there;  loaded each with a 1 ohm resistor.  One made 12 amps (good)
and the other made none (toxic waste).  Fortunately, I had a spare
battery, so I rebuilt the UPS and she's good to go.  

So what was causing the clock-precise power glitches?  Casting around
the house, I looked at the digital furnace timer.  The clock (battery
powered, feh) was off by 1 hour and 16 minutes.  The furnace is set to
come on at 5AM, when my wife gets ready for work.  It's been kinda cold
these last few days, so the furnace has started turning on for the 
season, but an hour and 16 minutes late.  Furnace blowers start out
at a dead stall, and the furnace circuit is on the same power leg in
the fuse box as the computer feed.  There seems to be an ohm or so
of extra resistance in the neutral leg of the PGE feed, so when a motor
stalls on the same power leg as the UPS, the power is glitched low
enough to trip the UPS.  Which promptly cuts out line, and starts 
attempting to make power from the (gutless) battery.

What is really fortunate, though, is that if the furnace timer had been
coming on at the correct time, and creating the glitch at 5AM, it would
have been right near the end of the backup cycle that starts at 4AM,
and this might have damaged my backup file system - certainly those
morning backups.  Backups are usually complete before 6AM.  So I lucked
out, actually.

The moral of the story is, sometimes weird-time precision is something
besides a computer ... 

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs