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Author Topic: Older electronics  (Read 243 times)

Weaver

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Older electronics
« on: June 26, 2018, 02:15:35 PM »

Say I wanted to buy an older router, modem or WAP or some other kind of electronic item and it has been in use for n years.

What is the likely downside compared to something nearly new? Let’s say that n = 1, 2 or 5 years? Any problems I am likely to run into with current performance immediately and also with longevity?
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sevenlayermuddle

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Re: Older electronics
« Reply #1 on: June 26, 2018, 02:56:49 PM »

I’d be wary of remaining life expectancy of modern electronics, beyond a few years.

Most common failure of modern electronic equipment in my experience is aluminium electrolytic capacitors.   

The manufacturers’ life expectancy for these components, at rated ambient temperature, is generally just a few thousand hours - often much less than one year.   Common temp ratings being 85C or 105C.   For every 10 degree reduction in ambient temperature below rated the life expectancy doubles, hence there are decades old capacitors still working fine, in old pocket radios etc, that stay cool.   unfortunately consumer modems and routers, along with other modern electronics, may run quite hot, hence cap failures more common after not many years.

Another problem on the horizon is lead-free solder, introduced in response to EU ROHS regulations.   It has been found susceptible to growth of tin whiskers.   I have never seen it with my own eyes, but I understand it can and does cause problems.

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Weaver

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Re: Older electronics
« Reply #2 on: June 27, 2018, 08:42:44 PM »

So this is the price of no-lead, whisker growth?

Two things:

One reason for me asking the question is that I was trying to work out whether it is a really bad idea to try and save a small amount of money by buying second hand stuff that has actually been used, versus stuff that is still boxed up and has never been even opened.

The second reason for my question was because I found a large box with several very expensive ZyXEL WAPs in it a while ago, and they have never been used. I bought some way back when and then lost track of them. So this means that the WAPs might still be in very good order then? And their age might not matter too much because they have never done any active duty?

I suspect that I should try hard to keep kit cool then?
« Last Edit: June 27, 2018, 08:49:24 PM by Weaver »
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sevenlayermuddle

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Re: Older electronics
« Reply #3 on: June 27, 2018, 11:42:15 PM »

My own understanding is...

Per capacitor failure, unused equipment is generally good.  By being cool, the caps are more likely to be fit and well.  Capacitors have other failure modes too, as do other components but I believe high ambient temps, ie appuratus that is on 24/7, is probably the biggest worry.

Per whisker growth, it gets more interesting. They grow slowly, the material gradually restructuring itself over time, more or less, in a simplified view, atom by atom.     Not sure if I could find the sources again, but I seem to remember reading that if equipment is ‘powered on’ at the instant a whisker causes a short, the whisker will be just a few atoms wide, and even the tiniest current flow will be enough to vapourise the whisker with no collateral damage.   If ‘off’ the whisker gets more of a foothold, with worse repercussions for other compoments once current does start to flow.

My only real experience of tin whiskers is in relation to another recently ressurected interest of mine, restoring old radios.   Certain early germanium transistors, specifically those of AF11x type, had fairly pure tin coatings on their cans and are so susceptible to whisker growth to extent that, by now, it is a fair assumption any single AF11x specimen will probably have shorted.   These things are now circa 50 years old, although I think they were already failing, less commonly,  by mid 1970s.   Will modern electronics be as badly affected?  Will it take that long?  Who knows. 

I emphasise, although I find it interesting, I am no expert in tin whiskers.   Not sure anybody is, as it seems to be (surprisingly) a poorly understood phenomenon.  But  I do understand that NASA, for example, are worried about whisker growth e.g.  per satellite and spacecraft longevity, in relation to the EU directives of noughties, mandating lead free solder.
« Last Edit: June 28, 2018, 12:27:39 AM by sevenlayermuddle »
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