On Mon, 23 Jan 2006 23:39:23 -0500, "Leonard Caillouet"
wrote:


"G-squared" wrote in message
roups.com...

Leonard Caillouet wrote:
OK, maybe some of you can see what I am missing or know something that I
don't that can shed some light on this one. We have a client that has
had
this Yamaha receiver and Mits HD ready set for a few years and just
switched
to Cox HD cable. The receiver has been working fine, switching both
component and composite signals into the set. Hooking up the SA box
through
the Yam (component signal) gives a pix in which the whites are "blown
out"
or "crushed" like the video is too intense. Black levels look normal.
The
effect is like looking at video that is not properly terminated at 75
ohms.
Other sources besides the SA box look fine using the same inputs on the
Yam
and Mits. Here is the catch. Hook the SA box up to the set directly and
it
looks fine. OK, so the Yam is the problem, right? Well, pulled it to
the
shop, assumed it might have a bad ground or something and checked,
re-seated
everthing in the vicinity of the video board. Threw every kind of source
at
it that I could, and the input and output looked identical, pix looks
fine
with every source 480i to 1080i on every one of 4 different technology
displays.

Put it back in the system assuming that we had missed something or maybe
a
bad cable or something and the same thing happened. I have not looked at
the output of the SA box yet, since we do not have Cox at the shop and
can't
get it. Guess I will be hauling a scope out to the site. Maybe someone
will come up with some ideas before I go.

The Yamaha seems to be a very straightforward buffered switch with about
60Mhz bandwidth. I could not detect any degradation in signals passed
through it and I confirmed it terminates at 75 ohms. Maybe the output of
the box is really hot and the Yamaha is not tolerant and clipping the
signal? Looks fine going directly into the set, however.

Any ideas?

Leonard

We came across some 'prosumer' gear at work that did not have correct
output termination which caused some aggavation when trying to connect
it in. In your case I'd take the source video into a BNC 'T' connector
into the input of your scope and then connect the terminator on the
other leg of the 'T'. If everyone is 'playing by the rules', the level
should drop by 6 dB and be 700mV without sync, 1 V with sync.

Good luck sorting it out.
GG


My first thought was unterminated video when I saw the symptom. We'll see
what the level actually is, but the TV handles it fine. My second thought
was that maybe the tri-level sync from the HD was getting distorted and the
Mits was not handling it properly. We have seen this issue in other brands,
but if there was a problem there it seems like the level would go the other
way if the set were trying to clamp to the second half of the tri-level sync
pulse. Maybe the SA box is not using the proper tri-level sync? Not
possible at this late date that they could do something so silly, is it?

Leonard

Could it be an output driver of the kind that require DC termination
to define the working point in combination with a DC blocked input?
I have seen some incompatible S-video connections and I heard of this
problem with certain units.
/Jan