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Electrical gremlins and tin whiskers

 
Old 11-22-2007, 12:09 AM
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alex70
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Default Electrical gremlins and tin whiskers

hi-

Any thoughts on the effects of the 'tin whiskers', the age of the 928 and all of our electrical gremlins besides the obvious? I'm wondering what minor major components that could be replaceded by a maintenance protocol. (just to reduce the frustration in dx, not sure of the regular electrical outputs showing norm are off due to these gremlins)

Sold my last 928 but wanted to contribute the thought


Link
http://en.wikipedia.org/wiki/Whisker_(metallurgy))

Just a thought to everyone trying to figure out the little guys (elec probs) that drive us crazy.

aka

dick

Last edited by alex70; 11-22-2007 at 12:25 AM. Reason: typo
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Old 11-22-2007, 12:23 AM
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alex70
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Just for notation, these little whiskers did bypass our NASA engineers and effect the throttle direction modules..


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Old 11-22-2007, 06:19 PM
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SteveG
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I'm glad you clarified what whiskers are. So what did NASA do about them?
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Old 11-22-2007, 07:06 PM
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karl ruiter
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Thankfully, tin whiskers should not effect our 928s. In the real early days of electronics they had huge problems with this. Basically what happens is that when the solder joint is put under stress it grows these whiskers. But the problem was solved long, long ago with the addition of lead to the solder mixture. Basically the lead makes the solder soft enough that it just deforms rather than extrude the tin. End of story right? Wrong. A few years ago some numnuts from Europe decided that having hazardious substances in electronics was bad, bad, bad. So that means no lead in the solder. Did they come up with another solution to the problem? Nope. They just regulated out the one proven solution. The rule is called ROHS (Reduction of Hazardious Substances), and is it a train wreck for electronics. I like the idea of making landfill safer, but this rule, the way it is written, drops the service life of most electronics assemblies from several decades to just a year or so. The rules went into effect in 2006 in Europe, and are also required in a few places in the U.S. Generally in the U.S. the rules are written much smarter. So, for example in California (as I recall) things like cell phones and T.V.s are required to conform, but other things (like cars) are not. This is a good way to tackle it because cell phones, for example, only have a service life of a couple of years anyway, while we all like the idea (from both a financial and environmental perspective) of cars that can stay on the road for 20 years or more. In Europe pretty much everything must be lead free. Some manufacturers have take the tact of going lead free world wide, while others produce differently for the different target markets.
I don't know what will happen when people start finding that they have to replace all the electronics in their cars every couple of years. Maybe they will change the laws. Maybe older cars will go up in value. I'm just glad it does not effect 928s.
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Old 11-22-2007, 09:02 PM
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Yep. The solder used in Porsche stuff Pre ROHS compliance (the last couple of years) should all be approx. 60% tin, 40% lead solder.

In comparatively low-impedance circuits, the whiskers are prone to burnoff. In higher impedance (CMOS circuits etc.) it's more likely to be a problem.

On the tin-plated circuit board traces, a brush with what resembles a (static-resistant!) toothbrush on any suspect boards should be all it takes to remove whiskers.

...Or a Gilette...

Keith
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Old 11-22-2007, 09:14 PM
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Always been a Wilkinson Sword man myself.
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Old 11-22-2007, 10:59 PM
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And there I was thinking you were talking about Hughes 601HP satellites.

Last edited by jon928se; 11-25-2007 at 02:46 AM. Reason: correction
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Old 11-24-2007, 02:46 PM
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Karl R , thank for the info,

rich
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Old 11-25-2007, 12:44 AM
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I helped build the Intelsat IV for Hughes
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Old 11-25-2007, 02:45 AM
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I just recall the stress my wife suffered when Galaxy IV among others went walkabout. Much frantic reassigning of services.

My memory above was wrong - Hughes 601HP - grew tin whiskers on the relay that switched on the back up brain - goodbye Satellites.

All they needed was the Jim B mantra - Relay Relay Relay
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