Re: [amsat-bb] Opps! D/C water ingress

[Franklin Antonio <antonio@xxxxxxxxxxxx>]

At 10:36 AM 8/5/2001, John Wilcox wrote:
>It now appears that water has entered into my CalAmp downconverter and is
>causing the problem. I have dabbed it out as much as I could but it does not
>appear to be enough to restore its original outstanding performance.

I don't have experience with CalAmp downconverters, but I have had 
experience with cell phones that have fallen into water.  One thing I've 
learned is that it takes a lot longer for these things to dry out than you 
would imagine.  Even if it looks dry, water has made its way into places 
you can't see.  I've had the experience of opening up a  cell phone, then 
letting it dry out in a slightly warm (150 degree) oven for 2 or 3 hours 
after which it didn't work, then found that it worked fine after being left 
in the oven for 24 hours.  (Turn the oven off before putting the electronic 
gizmo in there.  Just let the residual heat of the oven help the 
drying.)  I think it just takes a long time for things to really dry.

>  There also appears to be some sort of residue left from this attack..

I used to work on electronics that was installed outdoors.  I saw lots of 
cases of water ingress in electronics that was powered up during the 
ingress.  The combination of water and DC voltage is evil.  Water, unless 
it is distilled water, conducts electricity, and electrochemical things 
start happening.  These electrochemical reactions involve the tin and lead 
in the solder, and the copper in the circuit board traces.  You get various 
conductive salts.  (I'm not a chemist, so don't yell if I didn't get the 
terminology quite right.)  This allows the water to conduct more 
electricity, and so forth.  This will eat away traces if you let it go too 
long!  Meanwhile, it is as if someone has added some resistors to your circuit.

On the other hand, if the board was conformal coated, and water never got 
across live conductors, the residue might just be the normal residue one 
expects when dirty water evaporates.

I suggest you get a toothbrush and some alcohol (and maybe some water if 
that works better) and try to remove the residue from the circuit board as 
much as possible.  Especially where traces run close to one another.

>I have heard of folks putting electronic equipment into the dishwasher and

I would recommend against that.  Could destroy some components.

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