"Jerry G." bravely wrote to "All" (22 Apr 05 17:31:08) --- on the heady topic of "Re: 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.