video level problem? SA8300HD, YAM RXV1200, Mits WS-55809

[Leonard Caillouet]

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

 

[G-squared]

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

 

[Leonard Caillouet]

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

 

[Don Bowey]

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

I agree with the previous poster. I bet the TV has a termination on it's
input, which is why it handles the signal well. A lot of equipment has an
option to terminate, or not terminate in order to bridge equipment.

Don

 

[Jan B]

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

 

[Leonard Caillouet]

I agree with the previous poster. I bet the TV has a termination on it's
input, which is why it handles the signal well. A lot of equipment has an
option to terminate, or not terminate in order to bridge equipment.

Don

I am the OP and the termination is appropriate at 75 ohms.

Leonard

 

[Leonard Caillouet]

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

What do you mean by DC termination?

Leonard

 

[Tony Hwang]

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

Hi,
Receiver was doing fine and problem when Cox HD box is hooked up.
Logic tells me, I'd try another cable box first.
Tony

 

[Leonard Caillouet]

Hi,
Receiver was doing fine and problem when Cox HD box is hooked up.
Logic tells me, I'd try another cable box first.
Tony

That was the first thing we tried.

Leonard

 

[Jan B]

What do you mean by DC termination?

I mean a termination that works also at DC.
Some drivers need the 75ohms to give the correct DC-load (and levels).

At least some front projectors aparently has a DC blocked termination
(on S-Video inputs) and those units have a problem with each other.
This can be measured with a normal ohm-meter.
/Jan

 

[Leonard Caillouet]

I mean a termination that works also at DC.
Some drivers need the 75ohms to give the correct DC-load (and levels).

All component, composite and S-video should be terminated at 75 ohms.

At least some front projectors aparently has a DC blocked termination
(on S-Video inputs) and those units have a problem with each other.
This can be measured with a normal ohm-meter.
/Jan

Some units have the option of switching the terminating resistors on or off
to allow a loop out to another unit, where there should be proper
termination. This may be what you are talking about. Nearly all inputs are
coupled to the buffer stages through capacitors that block dc that can occur
as a result of the negative going sync pulses. This is one of the
advantages of tri-level sync used with HD...it has both positive and
negative going pulses that average out. Still, I have not seen an input
circuit in consumer electronics that was not capacitor coupled (after the 75
ohm terminating resistors).

Leonard