Message-ID: <3E188A57.3C76@sneakemail.com>
From: Mike Monett
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Newsgroups: sci.electronics.design
Subject: Re: Low leakage parts
References: <3200347.0301031546.5fbc6b41@posting.google.com>
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<3E184B38.588B@sneakemail.com> <93nqLeBSsFG+Ewlk@jmwa.demon.co.uk>
Date: Sun, 05 Jan 2003 14:41:11 -0500
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NNTP-Posting-Date: Sun, 05 Jan 2003 14:40:39 EST
Organization: Bell Sympatico
John Woodgate wrote:
>
> I read in sci.electronics.design that Mike Monett
> wrote (in <3E184B38.588B@sneakemail.com>)
> about 'Low leakage parts', on Sun, 5 Jan 2003:
>
> >Anything special about the alcohol? Some have mentioned that plain
> >store-bought isoprop is unsuitable, but I've cleaned keyboard switches
> >with it and they measured over 1 gigohm, which is the top range on the
> >HP3456A.
>
> Measure it after a day or so in a humid atmosphere. Some ionic compounds
> dissolve in alcohols and of course they dry out to the anhydrous form,
> which is often hygroscopic. Calcium chloride is a particularly
> significant example, because of its extreme affinity for water, but even
> the ubiquitous sodium chloride is slightly soluble.
>
> Of course, you may well have been lucky - up to now.
> Regards, John Woodgate
Well, the problem usually arises after a coffee spill. I have to take the
keyboard apart, unsolder the switch, then disassemble it. There are two
parallel plates separated by a spacer that looks like nylon. I was
surprised to find the initial resistance was quite low - perhaps 10k or
so.
Swishing it around in a glass with a small amount of isoprop seemed to
fix the problem, but keyboard switches are less demanding than some
applications:)
Mike