[rescue] mysterious hard hangs, two different sun4m's

[Eric Dittman]

> > HV lines under the floor?
> 
> What frequency do HV lines typically run at?  60hz would cause noticible
> interference in monitors, from my experence.  (previous employer had an
> office out in the plant with some sort of transformers on top of it. 
> Monitors would have horrible interference unless they were running at 60
> or 120hz refresh rates.)

Most are at 60Hz.  The magnetic field induced by the HV lines
can cause different types of problems.

My brother called me about a problem with a PC at a concrete
plant that was having problems only in the field.  The PC
controlled the truck scales.  The PC was supplied by the
company as part of the truck scales, so the PC was sealed
against dust.  The PC was located inside the scale house
which was air conditioned.

I first had them have the scale company put in a power
monitor.  Over a period of two weeks there were no power
fluctuations monitored at the PC (a power conditioner was
standard equipment).  The next step was an environmental
monitor.  The temperature and humidity were well within
the accepted ranges.  Monitoring the inputs from the scale
was the next step.  These lines were filtered and used
optoisolation and were clean.

As the final step I had him build a crude Faraday cage to
house the PC, keyboard, mouse, and monitor.  That worked
pretty well, so they had a company come in and build a
better permanent Faraday cage.  All is well now.
-- 
Eric Dittman
dittman at dittman.net
Check out the DEC Enthusiasts Club at http://www.dittman.net/