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PICList Thread
'[PICLIST] Dew Detector Reliability'
2001\01\04@134619 by Chris Carr

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In an earlier thread a remark was made that the Dew Detectors fitted to
VCR's went high resistance over a period of time causing the dew detector to
come on permanently.

I took the opportunity to check this with a colleague who repairs VCR's for
a living and he expressed surprise as he could count the failures of this
type on the fingers of one hand. As far as he could remember this problem
only affected ancient recorders such as my Panasonic NV7000 (Duh).

This got me thinking that perhaps the reliability of these devices is
affected by climatic conditions and the UK is a benign climate as far as
these devices is concerned.

Anyone care to comment ?

Regards

Chris

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2001\01\04@135634 by Chris Carr

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Forgot the Category in the Title, Second Try


In an earlier thread a remark was made that the Dew Detectors fitted to
VCR's went high resistance over a period of time causing the dew detector
to
come on permanently.

I took the opportunity to check this with a colleague who repairs VCR's for
a living and he expressed surprise as he could count the failures of this
type on the fingers of one hand. As far as he could remember this problem
only affected ancient recorders such as my Panasonic NV7000 (Duh).

This got me thinking that perhaps the reliability of these devices is
affected by climatic conditions and the UK is a benign climate as far as
these devices is concerned.

Anyone care to comment ?

Regards

Chris

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2001\01\04@144231 by Alice Campbell

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Hello Chris,

the best description of resistive sensors ive found:
http://www.figarosensor.com/details.html

from what they say, i think the problem is that the sensor
gets irreversibly poisoned over time, mainly with silicone-
type substances (*) (not the same as silicon, BTW).
basically, the more silicone around, the faster it dies.
using a silicone lube around these sensors sounds like the
kiss of death to me.

my impression is that its better not to get too emotionally
attached to this type of sensor.

alice
(*)Silicones are polymers in which organics groups, such as
methyl and phenyl groups are bonded to the silicone
    atoms in chains of inorganic siloxanes (-Si-O-Si-).
Possessing a host of unique properties including heat, cold
and
    wheather resistance, electrical insulation, release,
water repellency and defoaming properties, silicones are used
    throughout the following industries:
{Quote hidden}

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2001\01\04@145650 by David VanHorn

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You can "Do the Dew" without resistive sensors.

A clean glass plate is a specular reflector, unless covered with dew (or
dirt). Then it becomes a diffuse reflector.  A diffuse reflector scatters
light in all directions (like paper). A tight IR beam can be arrainged to
bounce off the glass, and miss the target, unless there is something on the
glass.
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2001\01\05@013549 by Roman Black

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Chris Carr wrote:
>
> In an earlier thread a remark was made that the Dew Detectors fitted to
> VCR's went high resistance over a period of time causing the dew detector to
> come on permanently.
>
> I took the opportunity to check this with a colleague who repairs VCR's for
> a living and he expressed surprise as he could count the failures of this
> type on the fingers of one hand. As far as he could remember this problem
> only affected ancient recorders such as my Panasonic NV7000 (Duh).
>
> This got me thinking that perhaps the reliability of these devices is
> affected by climatic conditions and the UK is a benign climate as far as
> these devices is concerned.
>
> Anyone care to comment ?


You bet! Here in Aust it's pretty common. I have been
fixing VCRs and other devices for many years, and I do
a couple of dew faults a month. Our temperatures
are much higher, especially in a closed TV cabinet with
a large screen TV and a VCR in a room at 32'c.

Humidity commonly around 70%+ in the warmer months.
And your friend is right, this is older VCRs that get
the dew fault. Mainly 10+ years. And 20 years like your
NV7000! Many of the new VCRs just don't have dew sensor,
so you won't see the fault on them! :o)
-Roman

Did you fix your VCR yet?

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2001\01\05@014625 by Nigel Goodwin

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In message <004201c0767e$80c7aba0$aace7ad5@dougal>, Chris Carr
<.....nyedKILLspamspam@spam@BTINTERNET.COM> writes
>In an earlier thread a remark was made that the Dew Detectors fitted to
>VCR's went high resistance over a period of time causing the dew detector to
>come on permanently.
>
>I took the opportunity to check this with a colleague who repairs VCR's for
>a living and he expressed surprise as he could count the failures of this
>type on the fingers of one hand. As far as he could remember this problem
>only affected ancient recorders such as my Panasonic NV7000 (Duh).

I've been repairing VCR's since VHS and Beta first came out, with a few
Grundig/Philips machines before that - I can count the number of dew
sensor failures on the THUMBS of one hand :-).

>This got me thinking that perhaps the reliability of these devices is
>affected by climatic conditions and the UK is a benign climate as far as
>these devices is concerned.

Possibly?, I've never heard of any problems in the UK.
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2001\01\05@024002 by Michael Rigby-Jones

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{Quote hidden}

Guess I must have been unlucky; I've had two of my own VCRs fail in this
way.  One was an Akai (I think) and the other was an LG.  Both sensors were
replaced with appropriate resistors.

Mike

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