Testing a Video Signal

[Mike Warren]

I am NOT telling you what you to do - only pointing out what
measurement
method would likely work.

Just for fun I added 5pF in parallel to one of the caps on the crystal and
now
all three of my monitors have colour.

I guess doing that can be a last resort, since it only takes a few seconds,
but it's certainly not an ideal situation.

 

[Phil Allison]

"Mike Warren"

Just for fun I added 5pF in parallel to one of the caps on the crystal and
now all three of my monitors have colour.

I guess doing that can be a last resort, since it only takes a few
seconds,
but it's certainly not an ideal situation.

** Guess that proves the point about the colour burst frequency being off -
beyond all possible doubt.

Tweaking the PCI card's crystal was suggested by ME to YOU just over
THREE days ago.

Rub, rub rub .....



..... Phil

 

[Mike Warren]

** Guess that proves the point about the colour burst frequency being off
-
beyond all possible doubt.
Yes.


Tweaking the PCI card's crystal was suggested by ME to YOU just over
THREE
days ago.

Rub, rub rub .....

LOL!

 

[JosephKK]

We have just purchased a quantity of PCIe video cards with
TV out (S-Video) and can only get a monochrome picture
from the S-Video output.

I have so far tried 6 different cards from 2 batches and
all have the same fault. Here are my observations?:

-Another brand of video card that used the same video chip
(nVidia 8400GS) works fine using the same driver.

-The driver /is/ set up correctly.

- The fault is there in both PAL and NTSC modes. Only one
of my monitors supports NTSC so I haven't done any extensive
testing in that mode.

-These cards produce a B&W picture on 3 separate monitors
(2 LCD and one CRT) All monitors work fine with the other
brand. The 15 year old CRT monitor will produce a colour
picture from this card for a few seconds when cold.

- Feeding the signal into a Canopus ADVC-100 video capture
device produces a colour picture on my computer.

Here are some pictures of the output. In the oscilloscope
pictures the top trace is the composite signal after my
passive S-Video to composite converter (just a 1000pF cap)
and the bottom trace is the chroma signal from the card.
www.mike-warren.net/tmp/DSO1-ECS-web.jpg
www.mike-warren.net/tmp/DSO1-Leadtek-web.jpg
www.mike-warren.net/tmp/TV-ECS-web.jpg
www.mike-warren.net/tmp/TV-Leadtek-web.jpg

This is a vectorscope signal produced using Adobe Premier
from the same colour bar signal. I haven't recorded the
output of the good card since I don't believe the
vectorscope will help with this problem.
www.mike-warren.net/tmp/Vectorscope-Leadtek.jpg

What tests can I do to try and work out what is wrong with
the signal? I tried to read the frequency of the colour
burst but I haven't been able to lock the DSO (Tek TDS1002)
on it so far.

The supplier claims there is nothing wrong with their cards
as no one else has ever complained.

Simply looking at the 4 scope traces is it clear that the cards
do not seem to produce proper PAL "phase alternate line" signals.

In particular the "cheaper?" cards may not bother to invert the
chroma burst as would be needed to maintain proper chroma.

 

[JosephKK]

Phil,

yes agreed, but since Hsynch and subcarrier bust are phase locked to
each other, the error expressed in % should be the same for both. So
if the H synch is very close to correct, the color burst should also
be very close to correct..

Mark

Assumption unjustified. PAL is seriously different from NTSC.

 

[JosephKK]

Thats is nonsense.
1) The color subcarrier does not need to be locked to H,
many systems do not do this.
2) for PAL it is 25 Hz offset anyways



Total crap, any frequency counter will measure the free running Fc,
only if it is way of will it cause the PLL not to lock.

Maybe you do not know, but just for the fun and the others who want to learn
and not put out crap here, in the old VHS system there could
be huge variations in H timing due to the mechanical nature of reading
from a tape with a rotating head, while the Fc was exactly within specs.
How is this done:
The color is recorded as a lower frequency superimposed on the FM modulated
BW video, the FM behaving like like RF bias was in audio tape recorders,
and that frequency was obtained by mixing *down* the chroma with an oscillator
locked to a multiple of H.
On playback that oscillator was also locked to H, and used to mix-up thechroma
back to 4,43 MHz.
As H changed due to mechanical issues, and so did frequency of the chroma from
the heads, the mixed product was stable again.
In the whole process there is NOWHERE a need for Fc to be locked to H,
H frequency would vary wildly, and Fc would be constant.

In PAL one of the quadrature modulators is switched 180 degrees every line.
That causes a burst phase change of +45 / -45 degrees every line.
In the receiver, when the PPL is locked, that signal appears on the PLL
output as a H/2 (7.8kHz) signal.
This 7.8 kHz is logical ANDed with that from a H flipflop that flip flops every H pulse,
to cause it to flip in the same phase as the transmitter's, it is used to switch one of the
demodulation axis 180 degrees.
The level of this 7.8 kHz signal is used to activate the color circuit.
If the PLL is *not* locked, there will be no 90 degrees burst swing detected,
no 7.8kHz, and the color will be switched off.
You need a good lock for color, apart from a shitty noisy digital Tek
scope (a cheap analog 10MHz displays video better), there is too little burst
it seems, so the color killer comes in.

'bout the only sensible thing you have said.

Now I hope you just learned something but I doubt it.

If I was the manufacturer of that card, and sombody came complaining
withh a shitty signal like that generated by a totally absurd S-video interface,
I would take the card back as I do no want to sell to idiots.



No you are!

Jan -5 points for confusing many different video recording and
transmission methods.

 

[JosephKK]

That sucks even more.

Damn Jan, what has turned you into such a wanker recently?

 

[JosephKK]

If the frequency was off but close enough to allow the oscillator to
partially lock to it, wouldn't that cause the hue to alternate?

I don't happen to have the standards to reference, but i seem to remember
that the receiver / display specifications required a much larger lock-in
range than is allowed for broadcast chroma carrier variations. Of course
computer display cards have much more variation than broadcast transmissions.

 

[Phil Allison]

"Joseph Klu Klux Klan


** **** off !!!!!!!!

you FUCKING LUNATIC wog IDIOT !!!!

 

[Phil Allison]

"Mark Google Monkey Moron "


** **** OFF GOOGLE MONKEY IMBECILE


**** OFFF !!!!



...... Phil