Testing a Video Signal
in [Design]
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From: Mark on 19 Jan 2010 17:38 > ** The OP is in Australia an so using PAL monitors. > > Another trick is to take a known good video > signal and loosly couple the UUT video to it and you will see the > video sync drift through. If the H sync drift less then 1 frame per > sec or so, it is probably close enought that a monitor should lock to > it. > > ** Horizontal synch is NOT the problem. > > Colour sub carrier synch IS !! > > ..... Phil 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
From: Jan Panteltje on 19 Jan 2010 18:17 On a sunny day (Tue, 19 Jan 2010 14:38:11 -0800 (PST)) it happened Mark <makolber(a)yahoo.com> wrote in <8c26a9e1-4159-499c-81df-49ba6863759f(a)p23g2000vbl.googlegroups.com>: >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 Very often H and color subcarrier are not even locked. And just do some calculation what difference in H you need to get a few cycles of in color subcarrier. The PLL that locks to the burst in the monitor or receiver does not look at H at all, except for opening a gate to gate out the burst.
From: Mark on 20 Jan 2010 12:28 > > yes agreed, but since Hsynch and subcarrier bust are phase locked to > each other, the error expressed in % should be the same for both. > > ** Meaningless drivel. > > A monitor's H-synch has a wide tolerance while the colour carrier synch > range is very small. > true but irrelevent.. if you reacall I was suggesting the op measure the H sync error in order to determine the color subcarrier errors. They will be the same when expressed in % and the H sync is easier to measure. take care Mark
From: Mike Warren on 20 Jan 2010 16:48 Jan Panteltje wrote: >I would take the card back as I do no want to sell to idiots. LOL! Thanks. I hadn't been called an idiot today, yet. :-) You are indeed fortunate to be able work in an area where you can use the best theoretical techniques at all times and are not required to do things by the cheapest method that gets the job done. I'm not sure why you are fixated on the combiner when I have stated several times that the problem still exists when I connect the S-Video cable /directly/ to the S-Video input of the monitor. Some more information for anyone who's interested: I was able to get lock on the colour burst and measure it with the cursors on the Tek. I get 4.44MHz on the good card and 4.42MHz on the bad ones. Unfortunately this is only a one step difference of the cursor position so is not an accurate indication. I could discern /no/ difference in the timing of the H-sync between the 2 cards. The chroma level is within the measurement error of my Tek between the 2 cards as well. The manufacturer is looking into the problem. -- - Mike
From: Mike Warren on 20 Jan 2010 17:02
Paul Hovnanian P.E. wrote: >Didja try another s-video cable? Maybe the chroma pin is loose in a >connector. Yes, early on, but it is not necessary since I can see the chroma signal at the other end of the cable and the same cable was used for both the good and bad cards. My comparison is between one card made by ECS which works fine and 6 cards made by Leadtek which do not work properly. Both cards look nearly identical in layout and have probably just been copied from the reference design. I have previously used 35 of the ECS cards without any problems, but can't get any more of them. -- - Mike |