"Jerry G." bravely wrote to "All" (22 Apr 05 17:31:08)
--- on the heady topic of " ViewSonic E71 with extrange sympthoms..."
It isn't my intention to spark a debate about MTBF but one must
remember that this specification is derived from an accelerated
environmental simulation and is not therefore a real world value but
only an estimate. My point being that electrolytic capacitors are
basically self-healing and reform themselves when in use. Thus it is
expected they should hopefully last longer than the MTBF figure and
typically they do.
However in general, it can be argued that problems come about when
parts are used at their extreme limits. For instance using a 500mW
transistor to dissipate 500mW, and then placing an electrolytic
capacitor glued up against it, as we often see, is asking for trouble.
Please explain, why some idiot with a degree decides to place an
electrolytic capacitor inside the U shaped space formed by the
heatsink on a vertical output driver? This type of raging lunacy
abounds in the design of consumer equipment and too much to list!
You will no doubt agree that any device which is run at its limit
ratings will deteriorate more quickly. Conservative derating of
manufacturer specifications will result in equipment that will work
practically forever. Clearly this is counter-intuitive in a throw-away
consumer society. And yes, if well made and used conservatively, even
electrolytic capacitors can last virtually forever.
The reason why there ever was a sevice industry is because
manufacturers cut costs by cutting corners, designers make mistakes or
overlook unforseen conditions, and the equipment is not resistant
enough to user abuse. There was a time when tubes wore out and
required regular replacement but about the only tube left is the CRT
and these aren't replaced very much any more. About all that should
wear out are mechanical assemblies.
How many googleplex of cycles can one expect a digital transistor
switch to toggle before failing using a conservative under-rating?
I own equipment which still has the same ratings today it settled at
shortly after being made. The age has not hurt it a bit but I also
acquired garbage made in the past few years that is now in the dump.
JG From: "Jerry G."
JG Xref: aeinews sci.electronics.repair:46272
JG With the stresses that electronic components have during their life
JG span, they slowly will deteriate with use, and over time. This gets in
JG to MTBF factors (Mean Time Between Failure) factors. There are many
JG factors that will contribute to the MTBF factor of any type of part
JG that is electronic, or mechanical.
JG In the case of capacitors, under normal use in warm environments, or
JG where they are under strong electrical stress, they will slowly go off
JG value with time. Sometimes they can also become resistive, and thus
JG take on characteristics of being shorted, or they can simply degrade
JG in their reactance.
JG If electronic components do not wear down or deteriate with use and
JG time, then you should explain to me, why over time, they go out of
JG specifications to the point where they are not able to work properly,
JG or fail completely, and must be replaced.
JG If electronic components did not deteriate, or fail over time and use,
JG this group, and the complete service industry would never have
JG existed!!!
.... Transformer designers take turns doing it.
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