[mythtv-users] HDHR in harsh enviroments (was:OT: OTA HD )
beww at beww.org
Fri Dec 26 21:21:25 UTC 2008
On Friday 26 December 2008 12:30:35 David Brodbeck wrote:
> On Fri, December 26, 2008 9:40 am, Brian Wood wrote:
> > I would expect that sort of high temp environment not to cause immediate
> > failure, but rather to decrease the MTBF and result in failure before you
> > might otherwise expect it. It might be difficult to trace this directly
> > to the operating environment.
> That's the most likely scenario, but in extreme cases you might get
> thermal runaway, which can destroy transistors very quickly. It depends
> on whether there are any semiconductors in the HDHR that dissipate a lot
> of power.
In case anyone's interested:
"Thermal Runaway" happens because the current through the device causes
heating, and increased temperature causes the internal resistance to drop,
thus increasing the current flow, which increases the heating effect which
increases the temperature, which increases the current, which...
You get the idea. It is not a good thing.
I wouldn't think an attic would get hot enough to cause this, but if the
airflow was poor, it might. Of course for most of the year attics here in
Wyoming probably cause more cryogenic effects than overheating.
I wonder how a superconducting HDHR would perform.
I recall early reports of HD-PVRs getting very hot, people describing them
as "too hot to hold". I never had this problem with my unit.
For most electronics, not designed to operate at very high temperatures (like
vacuum tubes are), a good general rule is that if it is too hot to hold your
finger on it is too hot.
I'd guess that folks running Myth systems do not utilize too many vacuum
tubes, and some of the younger members of this list might be vague on exactly
what a "tube" is :-)
beww at beww.org
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