[mythtv-users] Component quality, was: HDHR in harsh enviroments

[Brian Wood]

On Friday 26 December 2008 22:55:42 Gordon McLellan wrote:
> If someone were to disassemble it and get some pictures, we can look
> at what makes it tick and get a better idea of the temperatures it'll
> work at.
>
> Most of your semiconductors are good to at least 85C (over 180F), that
> would be chips, transistors, diodes, etc.

Chips with ceramic cases, as opposed to plastic ones, are generally rated for 
higher temperature operation, mainly because the case is more stable with 
temperature variation.

You can't really expect a maker of consumer-grade products to use MIL spec 
components though, and I think we can safely assume that the lowest cost 
components available were used.

> The exception of course is 
> complex chips like CPUs, and LEDs which both require kidd gloves.  If
> the CPU is passively cooled at room temp (just a heatsink or maybe
> nothing), addition of a forced-air or larger heatsink will help there.
>  For leds, not much you can do there, just accept reduced lifespan.
>

Devices with passively cooled heatsinks are often sensitive to the position of 
the device, relative to its cooling vents. Often the best position is not the 
logical one, and sometimes setting a device on its side will result in better 
cooling (the PS3 is a good example). Just remember that heated air tends to 
rise.

Obviously you want to be sure you do not block or otherwise restrict the 
airflow around and through the unit.

Early cable TV STBs had this problem. One of them had cooling vents on the 
top, in the same shape and size as a TV Guide, with the obvious result.

> Then you have passive components like electrolytic capacitors, which
> might only be rated for a working temp of 50-75C, after which their
> electrolyte boils and makes quite a mess.  Conversely the electrolyte
> can freeze, which might rupture the cap, but more than likely will put
> it out of spec in terms of its capacitance.

As with all electronic components, capacitors are available in many grades, 
but again I think we can assume that consumer grade parts were used.

Personally I'd be happy to pay a premium for a device designed with better 
quality components, but most consumers disagree with me, or at least the 
manufacturers think that they do. The best (or worst?) example of this is the 
crappy fans manufacturers tend to use. I'd be happy to pay another few 
dollars for good ball-bearing fans, but they are almost never available as a 
consumer choice.

-- 
beww
beww at beww.org