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,
On 14/01/2011 09:39, Steven Creswick wrote:
> Inge,
>
> I feel your pain. I had purchased a more expensive unit - supposedly
having
> a significant range from transmitter to receiver. Was going to place the
> transmitter by my windsock. Wrong! First Summer it became erratic. All
> manner of flux residues and funky things growing inside the transmitter.
> Don't know what flux was used, but they certainly used plenty of it. Was
> difficult to clean, but doing so has resolved all the problems except for
> range.
>
> I have to go way further West to get to the board assembler. Two words
come
> to mind - cheap, chinchy. Pretty mediocre quality.
>
> In my case, I did not get the value I expected to have paid for
>
> Could the screw plating [under the head] have been poor? ... add flux
> residues and humidity during shipment, and as Robert said - a wire
beneath?
>
>
> Steve Creswick
> http://www.linkedin.com/in/stevencreswick
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
> Sent: Thursday, January 13, 2011 7:01 PM
> To: [log in to unmask]
> Subject: Re: [TN] a different Friday quiz
>
> Inge,
>
> I will take a wild guess, there is copper under the screw somewhere,
right?
>
> Bob K.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
> Sent: Thursday, January 13, 2011 6:07 PM
> To: [log in to unmask]
> Subject: [TN] 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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--
Eric Christison
Consumer& Micro group
Imaging Division
STMicroelectronics (R&D) Ltd
33 Pinkhill
Edinburgh EH12 7BF
United Kingdom
Tel: +44 (0)131 336 6165
Fax: + 44 (0)131 336 6001
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