Dodgy tellys
 

The customer had a massive Philips telly in one living room, and a
smaller V-something flat telly/DVD combi in the other living room. I
took an instant dislike to the V-something. I thought it was terrible.
The house has a 16 channel RF system, and tuning in was a long slow
job, accompanied by alarmingly loud clicks and pops from the telly.
There was something indefinably odd about the set. It seemed to me more
like a computer screen with a poor quality TV card rather than an
actual telly. The picture was quite degraded, and certain channels had
vertical wiggly lines that couldn't be shifted. After a week the
customer rung up to enquire if I could 'improve the picture'. After I
reduced contrast and colour the picture was perceived as being
'better', but after another week the set developed a fault which at one
time would have been described as 'no sync'. I ended up ringing the
manufacturer/importer on behalf of my customer. (As you'll have
realised by now this customer is also a friend). V-something were
sceptical, saying that since the sets 'didn't have sync'and I was,
basically, talking rubbish. Eventually the set was replaced with a new
identical one. Again I went through the laborious tuning-in procedure.
After a month the TV set would produce a blue screen and nothing else.
The customer had a fairy serious barney with the retailer, who tried to
say that he would have to take it up with V-something. The retailer
said that V-something was in fact part of Sony, so that proved that the
TV set of good quality. In the end the customer was allowed to exchange
the set (and a few hundred quid) for a Sony that actually said Sony on
it. Tuning the Sony was magic. It autotuned everything quickly and the
process of shuffling the CCTV channels was simple and easy. The
customer was in no doubt that the picture was much better. I thought it
displayed similar digital artefacts to the V-something, but possibly
less offensively.But there was a problem, one I've never seen before.
The broadcast channels and two of the camera were fine. But the other
cameras had the fault that a 'ghost' chroma imaga (colour with no
luminance)drifted about to the right of the main image. It wobbled
about from side to side, gradually progressing rightwards. Turning the
colour right down produced a perfect monochrome picture.
I wonder if anyone else has seen this fault. The camera channels come
from 'Vision' V40 modulators, which are pretty good from all past
experience. I'm wondering if there could be something non-standard
about the video waveform from some of the cameras. The sync looked
quite normal on the analyser though. Since the customer wasn't very
concerned about the fault I didn't investigate further, but I'm
wondering now if I should have reduced the video gain or something. Hmm
.. . .

Bill

Sounds like cross-mod, but the timing jitter is a bit strange. If one source
was VHS playback the jitter would have been expected.

Maybe one or more of the cameras are using some dodgy reference oscillator
that is pulled off frequency, due to poor PSU regulation perhaps.
Whether that is likely with a ccd camera I don't know.

Was this flat screen combo one of those LCD jobbies with the DVD slot on the
side?
LCD's seem to radiate lots of nasties into there own aerial sockets.

I know you will have thought of, and probably eliminated all the preceding
ideas, I'm just "thinking aloud" as it were.



--
Graham.



%Profound_observation%

Graham wrote:
Sounds like cross-mod, but the timing jitter is a bit strange. If one source
was VHS playback the jitter would have been expected.
No it wasn't RF cross mod. The RF signal level had no effect at all on
the fault.


Maybe one or more of the cameras are using some dodgy reference oscillator
that is pulled off frequency, due to poor PSU regulation perhaps.
Whether that is likely with a ccd camera I don't know.
Pulled off what frequency? It's certainly the case that some cameras
were badly affected, some weren't, and off-air wasn't affected.

Was this flat screen combo one of those LCD jobbies with the DVD slot on the
side?
No it was a flat screen Sony telly, pure and simple.

I know you will have thought of, and probably eliminated all the preceding
ideas, I'm just "thinking aloud" as it were.
No I haven't thought of any of the above possibilities. All I know is
that the rather blurred-looking colour outline of any brightly coloured
object drifted over an otherwise normal picture. The blurred outline
was basically to the right and it jittered back and forth a bit. There
was a slow drift to the right. I should have photographed it. I will if
I go back.



--
Graham.



%Profound_observation%

Sounds like baseband video crosstalk to me. The 4.43 MHz colour
subcarrier from one source leaking capacitatively into the cable of
another. As you know, capacitative reactance decreases with frequency,
so the lower video frequencies don't leak as strongly.
But the blurred colour image was always from the channel that was on
screen at the time.

It could be an earthing problem. Check that all the screens are earthed
at both ends.
The only input to the telly was the RF feed.

I think it maust be something to do with the video waveform from those
particular cameras.

Bill

wrote in message
oups.com...

Graham wrote:
Sounds like cross-mod, but the timing jitter is a bit strange. If one
source
was VHS playback the jitter would have been expected.
No it wasn't RF cross mod. The RF signal level had no effect at all on
the fault.


Maybe one or more of the cameras are using some dodgy reference
oscillator
that is pulled off frequency, due to poor PSU regulation perhaps.
Whether that is likely with a ccd camera I don't know.
Pulled off what frequency? It's certainly the case that some cameras
were badly affected, some weren't, and off-air wasn't affected.

Was this flat screen combo one of those LCD jobbies with the DVD slot on
the
side?
No it was a flat screen Sony telly, pure and simple.

I know you will have thought of, and probably eliminated all the
preceding
ideas, I'm just "thinking aloud" as it were.
No I haven't thought of any of the above possibilities. All I know is
that the rather blurred-looking colour outline of any brightly coloured
object drifted over an otherwise normal picture. The blurred outline
was basically to the right and it jittered back and forth a bit. There
was a slow drift to the right. I should have photographed it. I will if
I go back.



--
Graham.



%Profound_observation%


The mushrooms you had with your full english breakfast, were they
supermarket ones or were they freshly picked from a field?

The mushrooms you had with your full english breakfast, were they
supermarket ones or were they freshly picked from a field?

Picked from a field.

My friend had some as well and later he thought he was an orange. That
was OK for a while, but then he tried to peel himself.

Bill

On 26 Sep 2005 03:51:07 -0700, "
wrote:

The mushrooms you had with your full english breakfast, were they
supermarket ones or were they freshly picked from a field?

Picked from a field.

My friend had some as well and later he thought he was an orange. That
was OK for a while, but then he tried to peel himself.

All fungus is edible. Some of it is edible only once.



Tim

Maybe one or more of the cameras are using some dodgy reference
oscillator
that is pulled off frequency, due to poor PSU regulation perhaps.
Whether that is likely with a ccd camera I don't know.
Pulled off what frequency?

I refer to the master clock oscillator in the camera that everything is
referenced to.
All the sync pulses, colour subcarrier , burst timings etc.
If its frequency 'hunted' slightly (for whatever reason) it would normally
go un-noticed as everything would change a corresponding amount would be
correct relatively.

However when mixed with an accurate signal,
either by cross modulation or baseband chroma leakage,
you would see the timing anomaly on the screen viz.
your horizontal swaying rather than the smooth slow sliding
that you would expect from two sources that weren't genlocked.



--
Graham.



%Profound_observation%

Sounds like baseband video crosstalk to me. The 4.43 MHz colour
subcarrier from one source leaking capacitatively into the cable of
another. As you know, capacitative reactance decreases with frequency,
so the lower video frequencies don't leak as strongly.
But the blurred colour image was always from the channel that was on
screen at the time.

You didn't say that.
Sorry Sir!

As you were describing a multiple camera
installation it was reasonable to assume crosstalk between two cameras
at baseband. It sounds like instability somewhere - the video signal
being radiated and picked up earlier in the chain. Doesn't really
explain the changes in chroma delay though.
Something else I probably only inferred rather than made crystal clear
is that all the other tellys in the house (all working from the same RF
system) have a perfect picture on all channels. So basically there must
be something about the video waveform from these particual cameras that
this particular telly doesn't like. Maybe I ought to adjust the video
gain on the modulators and see what happens.

Better get the scope out and have a look. You do buy some rubbish. The
security cameras I bought from Netto for twenty quid apiece have worked
perfectly.
I had a quick look at the sync and colour burst and they looked quite
normal. The analyser is really an RF device though, and that facility
is not particularly brilliant. It is really intended to help spot sync
pulse crushing due to overloaded single channel RF amps.

Anyway, I've blown it with the plums haven't I? Father has taken to
scrumping apples from a place he has found near a motorway. "Good for a
quick get away!" he cackles. 86 and still on the nick! I don't know!

Bill

It certainly sounds like some sort of instability/feedback in the PAL
decoder. Is is a whizziwoppy all-singing-all-dancing digitally processed
five foot plasma job or a grotty little ancient 14" portable?
The former. A Sony flat screen hang on the wall jobbie. Very nice
otherwise, if you ignore the fact that the picture isn't as good as
that on the front of a CRT.

Anyway, I've blown it with the plums haven't I?

Down to single figures as of today. Room in the fridge now for all the
half-squirrelled fallen apples and pears while I think what to do with
them.
I nearly ran a squirrel over today, near Crosspool transmitter. It
defied my force majeure almost to the bitter end. I think it might have
been deaf, in which case it would have been very politically incorrect
to run it over.

SHEFFIELD MAN RUNS DOWN DISABLED MAMMAL
-- Star





Father has taken to
scrumping apples from a place he has found near a motorway. "Good for a
quick get away!" he cackles. 86 and still on the nick! I don't know!

He wants apples as well? How many kg?
Dunno what he wants them for. Have you got some?

Bill