What's a VCR "Dew Sensor" look like?

[Peter W. Poorman]

Hi all;

I've got an old Fisher VCR (model 73) that has decided that there is internal
condensation -- the "dew sensor" light has come on and stays on. I was able
to backtrace the signal from the light to an IC, but am lost from there.

My suspicion is that the sensor itself may have failed. Does anyone know
what a dew sensor looks like, and where it might be inside a VCR?

Thanks! -- Pete
poo...@convex.com

[CyberPriestess]

In article <poorman....@convex.com> poo...@convex.com (Peter W. Poorman) writes:
>My suspicion is that the sensor itself may have failed. Does anyone know
>what a dew sensor looks like, and where it might be inside a VCR?

They never seem to be in a consistent location from one model to
the next, but I remember seeing one that looked like a little flat silver
square on its own mini pc-board.

[Carl Oppedahl]

The best thing to do (don't you do this whenever you acquire another
consumer electronic device?) is to order up the service manual from the
manufacturer. On my shelf are service manuals for my VCR, my fax
machine, my laser printer, my photocopier ... then you have them when
you need them.

The sensor will be somewhere around the place where the videocassette
sits when it is in the machine. If you look closely at a videocassette
when it is fully rewound you will see a path where light can pass all
the way through the cassette since the clear leader is at the beginning
of the tape. So you will find a light source at one end and a
phototransistor at the other end. Maybe that's it.

--
Carl Oppedahl AA2KW
Oppedahl & Larson (patent lawyers)
Yorktown Heights, NY
voice +1-212-777-1330

[Lou Sortman]

>In <poorman....@convex.com> poo...@convex.com (Peter W. Poorman) writes:
>
>>I've got an old Fisher VCR (model 73) that has decided that there is internal
>>condensation -- the "dew sensor" light has come on and stays on. I was able
>>to backtrace the signal from the light to an IC, but am lost from there.
>
>>My suspicion is that the sensor itself may have failed. Does anyone know
>>what a dew sensor looks like, and where it might be inside a VCR?
>

The dew sensors that I've seen tend to be on their own little metal or plastic
bit in the general area of the tape transport. It has nothing at all to do with
the light sources and sensors, and it does not come into contact with the tape.
It usually looks like a small (1 cm square) bit of pcb with two wires hanging
off of it. the active surface is usually matte gray or black.
--
l...@tfnet.ils.unc.edu (Lou Sortman) for(i=0; i<3; i++) puts(
"Janet! Dr. Scott! \n"
"Janet! Brad! \n"
Whoever dies with the most LEGO wins. "Rocky! <Uh!> \n");

[jasonLittle]

If yu tell me what it is, maybe I could tell you what it looks like. What do I
look like, a picture book?

[CyberPriestess]

In article <2uui30$f...@panix2.panix.com> oppe...@panix.com (Carl Oppedahl) writes:
>
>>I've got an old Fisher VCR (model 73) that has decided that there is internal
>>condensation -- the "dew sensor" light has come on and stays on. I was able
>>to backtrace the signal from the light to an IC, but am lost from there.
>
>>My suspicion is that the sensor itself may have failed. Does anyone know
>>what a dew sensor looks like, and where it might be inside a VCR?

>The sensor will be somewhere around the place where the videocassette

>sits when it is in the machine. If you look closely at a videocassette
>when it is fully rewound you will see a path where light can pass all
>the way through the cassette since the clear leader is at the beginning
>of the tape. So you will find a light source at one end and a
>phototransistor at the other end. Maybe that's it.

That's the end of tape sensor you are describing. The dew sensor
detects when there's too much ambient moisture in the set. If
you live in a really humid area - or for some other reason, maybe
the set sits in the sun and has started "sweating" inside. You
might just try drying the set out - open it up - is it actually
moist? That kind of thing.

[Paul Mills]

l...@tfnet.ils.unc.edu (Lou Sortman) writes:

>>In <poorman....@convex.com> poo...@convex.com (Peter W. Poorman) writes:
>>
>>>I've got an old Fisher VCR (model 73) that has decided that there is internal
>>>condensation -- the "dew sensor" light has come on and stays on. I was able
>>>to backtrace the signal from the light to an IC, but am lost from there.
>>
>>>My suspicion is that the sensor itself may have failed. Does anyone know
>>>what a dew sensor looks like, and where it might be inside a VCR?
>>

>The dew sensors that I've seen tend to be on their own little metal or plastic
>bit in the general area of the tape transport. It has nothing at all to do with
>the light sources and sensors, and it does not come into contact with the tape.
>It usually looks like a small (1 cm square) bit of pcb with two wires hanging
>off of it. the active surface is usually matte gray or black.
>--

I find it unlikely that the sensor itself has failed. It's such a simple
device. More likely the circuitry. When the resistance across the sensor
drops, (such as when moisture on it) the circuit should be triggered to shut
down the VCR.

--
/******************************************************************************
* * *
* W. Paul Mills * Compiler Bug: Any action of the compiler which *
* Topeka, Kansas, U.S.A. * I did not intend. It couldn't be *