Yes, I know that, have been analyzing a lot during the years, but this seems
a little different. Note: 1. the unit has never been exposed to any other
environment than inhouse atmosphere.
2. The screw is not in contact with anything else than copperless FR-4.
3. Only one screw has this corrosion.
Inge
On 14 January 2011 12:07, Mike Fenner <[log in to unmask]> wrote:
Some corrosion, once started, can self perpetuate by feeding on atmosphere
water and CO2, with no need for differential metals etc.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Eric Christison
Sent: Friday, January 14, 2011 10:48 AM
To: [log in to unmask]
Subject: Re: [TN] a different Friday quiz
I'd go for galvanic corrosion in a mildly corrosive atmosphere, or
possibly highly corrosive depending upon your taste in food.
You didn't ever drop it in a bowl of Kimchi did you, or that Icelandic
dish of basking shark marinated in caustic soda?
Imagine periods of high humidity and temperature changes where moist
contaminated (salty?) air is drawn into the enclosure where it condenses
on the screw head. I bet you have dissimilar metals connected together
which will cause corrosion and the condensing air will drip off the
screw head to move the corrosion products around the inside of the device.
Regards,
----- Original Message -----
From: "Inge" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>
Sent: Friday, January 14, 2011 12:06 AM
Subject: a different Friday quiz
>
> I bought a digital temperature equipment, consisting of a inhouse table
> unit and a outdoors unit. Cost = 25 USD. Cheap? Yes. But let's have a look
> on inside after the problem, which started just a few weeks. You can read
> the inside temperature, clock works, date works, and you can use the alarm
> and shift between the four channels, but the receiver does not take in the
> signals from the little sender on the wall any more. I dismantled the box
> and marvelled when I saw the shit I payed for. It's a wonder that there
> are any functions working at all! Now, what caused the dead receiver was a
> flow of iron from one screw (upper left corner ) . There is a bridge of
> corrosion products (brown and green) from the screw to the thermistor
> (RT) continuing to the rest of the circuitry. When I washed the card and
> dried it, the reciever worked again,
>
> Now, folks, here comes a question for the sharp TNetters:
>
> "How can the screw be so rusty and deliver iron ions when it's not
> connected to anything? It's just torqued into the plastic body. The other
> screws are identical, but have not been involved in anything. "
>
> The box has been on the kitchen table and has not been exposed to humidity
> or any else abnormal condition.
>
> The two 1.5 V batteries are removed on the pics.
>
> Hope the gregorian Steve will help me with the photos.
>
> /Inge
>
>
>
>
>
>
>
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