Yowtch! Video over Cat5 shocks!

[Chris Chapman]

Hey gang, I need some trouble shooting advice on this one.

It's that magic time for Commencement again, and the District uses our Theatre for overflow seating. We take a live video feed of our Commencement Ceremony and project it onto our RP screen. Nice for the gray hair crowd, since the theatre is air conditioned and the gym isn't. Anyway.. I digress.

The inhouse video distro system is, to put it bluntly, sucky. Last year we ran a video over Cat5 (RJ45 Connections) to the projector postion to get a clean video send. As soon as commencement ended last year, we struck the gear, and it has patiently sat in a box for 12 months.

This year, as we set up we run into this snag. The video feed has a rolling band in it, indicitive of a ground problem. SO when I grab the BNC connector to disconnect the video send to trouble shoot it, ZAP. Got shock #1. As I troubleshoot on the projector end, every time I ground out grabbing the physical end of the cable, ZAP. Hmmmmm. On the send side, as we clean up our sources I run into this interesting issue. When I take the video lift off of a stand alone DVD player, no roll, no zap. As soon as I connect to their Video mixer or a source connected to their mixer, ZAP. I tried placing the mixer on different power and the zaps continue. SHould I (ulp) try to lift the ground on the mixer to eliminate the ground issue (hopefully) or try a different source?

The Video over Cat 5 has NO power on it, so the fault has to be coming from the Video send side, right?

Thanks for any advice on this one, video is not my baliwick.

-Chris Chapman
TD, Greenville Performing Arts Center

 

[Footer]

have you change out the cat5 cable?

 

[Chris Chapman]

Haven't done that. It's over 500 feet, run thru a drop ceiling. One word. FUN. I don't think it's the Cat 5, because the roll and the zaps go away based on the source.

-Chris

 

[derekleffew]

...As soon as I connect to their Video mixer or a source connected to their mixer, ZAP. I tried placing the mixer on different power and the zaps continue. ...

Exchange/replace the switcher; or add a Humbucker at the projector.

 

[cutlunch]

You shouldn't get an electrical shock off Video leads as the Video signal is only about at 1 Volt.
I would ask them to get the electrical safety checked on their mixer.
There could be a live wire wire loose in the unit which has contacted the signal earth but there is not a working
electrical earth to blow the fuse.

Until they have the safety checked on the mixer tell the management it can't be used and hire another. It's not worth anyones safety.

 

[museav]

When I take the video lift off of a stand alone DVD player, no roll, no zap. As soon as I connect to their Video mixer or a source connected to their mixer, ZAP.

If the DVD player is in the same location and off the same power as the switcher then that tells you quite a bit.

I tried placing the mixer on different power and the zaps continue. SHould I (ulp) try to lift the ground on the mixer to eliminate the ground issue (hopefully) or try a different source?

No, that would be a code violation and a safety risk. Based on the comments regarding the DVD player and other sources, if you can use the same power and cabling with a different source and not have the problem then it does not seem to be an inherent power or grounding problem and is almost certainly in some way tied to the video switcher.

There are some camera systems that multiplex power and other signals onto the coax so you can have power on a video cable, but that is only with certain systems and pretty much exclusive to the inputs to CCUs (Camera Control Units), I would not expect it to be applicable to switcher outputs.

 

[kwotipka]

You have a potential of ground between the two ends that did not exist in the past. In other words, the ground on one end of the line is better then the other . When you connect your video equipment to it, the voltage tries to ground down the Cat5 cable to the other end where the ground is better.

This is something that an a qualified electrician needs to check out as there are other problems then just a simple ground loop in your video.

kw

 

[ruinexplorer]

You shouldn't get an electrical shock off Video leads as the Video signal is only about at 1 Volt.
I would ask them to get the electrical safety checked on their mixer.
There could be a live wire wire loose in the unit which has contacted the signal earth but there is not a working
electrical earth to blow the fuse.

Until they have the safety checked on the mixer tell the management it can't be used and hire another. It's not worth anyones safety.

I concur. You need to also make sure that's not damaging your projector or other video equipment. I saw power run down a video line once and it fried quite a bit of equipment (problem was bad power from a hotel drop box).

 

[FMEng]

This could simply be a difference in ground potential between the two buildings. There are such things as video ground isolation transformers. You would insert it in the video line at either end. Try Markertech.

 

[museav]

This could simply be a difference in ground potential between the two buildings. There are such things as video ground isolation transformers. You would insert it in the video line at either end. Try Markertech.

I would agree, however the comment that the problem occurred only with the switcher and not with other sources at the same location seems to tie the problem to that one device. It might be interesting to know what happens if you used a separate wire to ground the switcher chassis and/or video output ground back to the ground connection where it is plugged in, If you get any voltage there then it would seem to be a serious device problem.