VCR head cleaning sensor? How does that work?

[William R. Walsh]

Hello all...

I own a relatively late model Panasonic VCR. Last night I went to play a
tape (the VCR had been sitting idle for a while) and the picture came up as
mostly snow with good sound. I knew immediately that the heads probably
needed a good cleaning, so I took the VCR out and put it on the bench to
clean it up.

However, before taking it out, I noticed that the VCR was displaying an on
screen message stating that the heads probably needed to be cleaned and that
a cleaning tape should be used.

Now the video/audio/erase heads are clean and the VCR is working nicely.
However, I am wondering how the VCR "knew" that the picture quality was
poor? I don't think it was a simple timer-triggered event.

William

 

[b]

Hello all...

I own a relatively late model Panasonic VCR. Last night I went to play a
tape (the VCR had been sitting idle for a while) and the picture came up as
mostly snow with good sound. I knew immediately that the heads probably
needed a good cleaning, so I took the VCR out and put it on the bench to
clean it up.

However, before taking it out, I noticed that the VCR was displaying an on
screen message stating that the heads probably needed to be cleaned and that
a cleaning tape should be used.

Now the video/audio/erase heads are clean and the VCR is working nicely.
However, I am wondering how the VCR "knew" that the picture quality was
poor? I don't think it was a simple timer-triggered event.

William

don't know for sure, I suspect it monitors/compares the fm signals from
the 2 video heads ??
-B.

 

[William R. Walsh]

Hi!

don't know for sure, I suspect it monitors/compares the fm signals from
the 2 video heads ??

Oh, yeah. I can't easily get at the model number right now, but I probably
should mention that it is a 4 head Hi-Fi stereo unit.

William

 

[Kim Cole]

Hello all...
.

Now the video/audio/erase heads are clean and the VCR is working nicely.
However, I am wondering how the VCR "knew" that the picture quality was
poor?

THE SAME WAY IT "KNOWS" YOU ARE A HOMOSEXUAL.

 

[James Sweet]

Hello all...

I own a relatively late model Panasonic VCR. Last night I went to play a
tape (the VCR had been sitting idle for a while) and the picture came up as
mostly snow with good sound. I knew immediately that the heads probably
needed a good cleaning, so I took the VCR out and put it on the bench to
clean it up.

However, before taking it out, I noticed that the VCR was displaying an on
screen message stating that the heads probably needed to be cleaned and that
a cleaning tape should be used.

Now the video/audio/erase heads are clean and the VCR is working nicely.
However, I am wondering how the VCR "knew" that the picture quality was
poor? I don't think it was a simple timer-triggered event.

William

Usually that sort of thing just triggers after a set number of hours of
play time, it may do something more advanced though.

 

[Dave D]

Hello all...

I own a relatively late model Panasonic VCR. Last night I went to play a
tape (the VCR had been sitting idle for a while) and the picture came up
as
mostly snow with good sound. I knew immediately that the heads probably
needed a good cleaning, so I took the VCR out and put it on the bench to
clean it up.

However, before taking it out, I noticed that the VCR was displaying an on
screen message stating that the heads probably needed to be cleaned and
that
a cleaning tape should be used.

Now the video/audio/erase heads are clean and the VCR is working nicely.
However, I am wondering how the VCR "knew" that the picture quality was
poor? I don't think it was a simple timer-triggered event.

William

A pure guess- maybe it just analyses the signal strength picked up by the
heads, and/or detects sync disturbances.

Of course, how it differentiates between dirty heads and bad tapes (if
indeed it does) is another matter.

Dave

 

[Cliff top]

there are 2 ways the manufacturers use to achieve blocked head detection.

For / during recording: mostly used on camcorders, not usually on home deck
VCRs
The unit detects small differences in the current/frequency response as its
recording, since a blob of oxide bridging the gap is a bit like a short
circuit at the frequencies being written and the effective load is thus
higher. Its not meant to be an exact science, more just an indication. Some
tape types can give spurious warnings unnecessarily however.

For Playback... thats easier.. it knows what signal level should be output
by the 2 video heads as they switch alternately. When 1 or other goes very
low output - as is usually the case when 1 gap is blocked, the 'clean heads'
mesage is displayed.

AW