Testing a Video Signal
in [Design]
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From: Mike Warren on 17 Jan 2010 21:14 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. -- - Mike
From: Michael A. Terrell on 17 Jan 2010 21:55 Mike Warren wrote: > > 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. S-video has seperate Luminance & Chroma channels. You need both to get a color image. If you are feeding a composite monitor, you need a S-video to composite adapter. <http://www.tkk.fi/Misc/Electronics/circuits/svideo2cvideo.html> shows a simple circuit. > 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 color burst in NTSC is only about seven cycles of 3.57954545 Mhz per frame. there is no way to read it during that time. You would need to read it in the monitor after it is regenerated in the chroma circuits > The supplier claims there is nothing wrong with their cards > as no one else has ever complained. > > -- > - Mike -- Greed is the root of all eBay.
From: Mike Warren on 17 Jan 2010 22:01 Michael A. Terrell wrote: > >Mike Warren wrote: >> >>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. > > > S-video has seperate Luminance & Chroma channels. You need both to >get a color image. If you are feeding a composite monitor, you need a >S-video to composite adapter. Thanks for the reply. As I explained, I'm converting through a 1000pF capacitor. This have been sufficient for me for over 6 years, and anyway I have the same problem feeding into a S-Video input to the monitor. -- - Mike
From: Michael A. Terrell on 17 Jan 2010 22:15 Mike Warren wrote: > > Michael A. Terrell wrote: > > > > >Mike Warren wrote: > >> > >>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. > > > > > > S-video has seperate Luminance & Chroma channels. You need both to > >get a color image. If you are feeding a composite monitor, you need a > >S-video to composite adapter. > > Thanks for the reply. As I explained, I'm converting through > a 1000pF capacitor. This have been sufficient for me for over 6 > years, and anyway I have the same problem feeding into a > S-Video input to the monitor. That may be too much capacitance. You are working with siglas in the 3.5 MHz range and may be coupling too much of the Luminance signal into the chroma channel. I've seen as little as 47 pF used. -- Greed is the root of all eBay.
From: Phil Allison on 17 Jan 2010 22:22
"Mike Warren" > > 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. > > > -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. ** The symptoms fit with a colour sub carrier frequency that is too far off for your monitors to lock onto. The allowed error ( for a broadcast signal ) is only 5 Hz in 4.4MHz or about 1ppm - which is way better than an un-trimmed crystal can provide. Being only a 10 cycle burst means measuring it directly is not possible. If the PCI card uses the computer's clock frequency for all timing, then you are stuck. If there is an on board 4.43MHz crystal - maybe you can tweak it a bit. ..... Phil |