Building Monitor Distribution Issues

[CBR372]

Hey guys,

So in my building we have a Sony PTZ camera that goes into and Extron A/V Distribution amp (this guy) then from there it is distributed around the building to different locations using COAX cable (Lobby, offices, backstage etc...)

However recently our signal to the Lobby TV went haywire (Flickering image, sometimes none at all, lots of distortion). So we went to look at our DA and looked at the BNC connector on the cable that ran to the Lobby tv and as it was kinda loose we decided to replace it. It fixed it monetarily but every now and again it goes back to the same issue. But now all of the outputs are doing it. TV's in our offices have the same flickering distorted issues. (It almost looks like the lines you would see when fast forwarding or rewinding a VHS tape)

I've messed with the gain and EQ and neither of those helped (Which by the way an explanation of what exactly EQ does in terms of video would be nice)

There's a 75 ohm and High Z switch which it seems to only want to push signal to the monitors when its switch to High Z (again an explanation of what this switch is doing would be great!)

Most the monitors were working before I went up there and touched the DA (minus the lobby) so what has caused all of them to start spazzing out now? Is my DA bad (why did it go bad a soon as I touched it?) or is there another issue at play?

I've got a few very large events coming up here in August so I want to get this fixed before then but I also don't want to go out and get a new DA if that's not what is causing these issues.

Any insight is appreciated!

 

[techietim]

I don't have loads of experience in video but it does sound to me like an issue with the distributution amp.

Can you be sure that it's not this playing up? Have you got a spare or equivalent you could try?

 

[museav]

Well, if you had one questionable connection then there is always the possibility that there is more than one and simply physically working on or around the DA may have affected them.

The input termination switch relates to the "LOOP THROUGH" connector. The incoming video signal needs to see a proper termination and if you are 'looping through' the DA input to another device then that termination is provided by the subsequent device while if you are not 'looping through' then the proper termination needs to be provided at the DA. So if you are using the "LOOP THROUGH" connection to feed another unit or monitor then the termination switch should be in the up or "HIGH Z" position while if there is nothing connected to the "LOOP THROUGH" connection on the Extron DA then the switch should be in the down or "75 Ohm" position in order to provide the proper termination. It is rather unlikely but the fact that you get signal to the outputs only with the termination switch in the "HIGH Z" position also leads me to suggest making sure the incoming signal is connected to the "INPUT" rather than the "LOOP THROUGH" connection.

Cable losses typically increase with increasing frequency and thus over longer cable runs you can have significantly greater losses for the higher frequency portion of the video signal. Video EQ is used to compensate for those frequency dependent losses by boosting the higher frequency portion of the signal (or cutting the low frequency portion).

 

[CBR372]

The camera feed does go into the input. I am starting to think the DA box is going. As of right ow it is all working perfectly. But it seems that if anyone even thinks of the DA in a bad light it will start acting up.

Got any recommendations of another DA It needs to be BNC connectors for Composite (Coax cable) signal. It needs to also have at least 5 outputs.

 

[ruinexplorer]

Before replacing it, I would check with Extron about servicing it. They are very good at keeping their equipment good. I have had to send DAs to them in the past and it generally was a warranty fix, costing me nothing but shipping. They are usually very fast in their turnaround time as well.

 

[museav]

Devices can go bad, however the more comprehensive problems apparently starting when you messed around with the DA connections and settings suggests it is more likely to be a connection or setting issue. A questionable connection that was bumped, something set too high or too low, etc.

You can get a cheap Comprehensive, TV One or Shinybow five or six output composite video DA for $100-$150, but those are not going to have EQ and more limited, if any, gain adjustment. Some of them will probably be true Distribution Amplifiers in that they may compensate for the five or six way split losses but will not provide any other signal gain or processing.

 

[FMEng]

I'm suspicious about whether the culprit is the DA or possibly bad terminations of the cables. Buy a BNC female-female "barrel" adapter to allow you to bypass the DA by feeding the camera directly to one monitor cable at a time. If that works, wiggle things to make sure the cables are OK. If that works and the DA doesn't, then you will know what the problem is.

Twist-on BNC connectors are notorious for problems. Crimp connectors are very reliable, provided the connector used is rated for the exact type of cable and the tool and die matches the connector, along with a proper stripper. The tools are expensive, so it would make sense to hire a contractor if the terminations need redoing.