weird problem that i cant get my head around

[griffonsystems 0]

4 outdoor cameras on coax to a quad in a trailer in a scrap yard, out of the quad and back to the dvr in the building office next door (power to the cams are homerun back to this office direct into an altronix 24vac supply) - total run not over 250ft. when i connect an lcd to the quad for the monitor in the trailer it puts power (i didnt put my meter on the coax to check last time) or something onto the line where you see a horizontal line flipping through the picture like it would look if there were power on on the coax. now when i put a tube tv or monitor off the quad there is nothing and all is good - how to get around this, they want an lcd for viewing there?

 

thanks,

 

pg

[3RDIGLBL 0]

I don't have a reason for it but maybe something that will bandaid it.

 

I assume that you are using a VGA to VGA connection? Does the LCD have a DVI connection as well?

 

I'm wondering if you use a DVI to VGA adapter if you can try connecting the LCD to the Quad via the DVI instead to see if this would address it.

 

There may also be a sync problem between the LCD and Quad where the tubes are not sensitive to it. The issue may very well be the quad and not necessarily the LCD. Have you tried a different brand LCD?

 

You say possibly putting voltage on the coax but do you see these lines in the actual recording or just on the LCD display during live view? This could definitely help to narrow down where this would be coming from.

 

Is there a video out on the DVR itself? If so do you see these lines when connected there?

 

Not sure if I helped but maybe got you thinking about it a little more.

[Jim Barrett 0]

Is the line on the LCD flipping or drifting? Kinda sounds to me like a ground loop problem if it's drifting. If it's flipping probably some sort of sync interference I should think. Most of these LCDs have a power converter kinda thing (highly technical term, I know) don't they?

I guess I'd uncouple the cable shield of the video signal at the LCD and see if the problem clears. If it did I think that would indicate a ground loop.

Presuming we're talking a coax connection?

[scorpion 0]

What you have is a weak ground loop issue.

 

You have two different grounding points. One at the multiplex, and one at the DVR.

 

The tube tv is more forgiving then the LCD. The ground loop is there. You just really have to look at it.

 

There are some LCDs that will look minor, and there are others that just look butchered off the same feed.

 

I tried one of those video splitter / amplifier (composite) hoping that would tame it down. It did not.

 

You will need a ground loop isolator. That is the only way to fix it. You could power both devices of the same power! How long of an extension cord will you need???

 

what do you think?

[jeromephone 6]

I have had similar problems with the Altronix power supplies. I either power up using seperate power supplies for small jobs or go to the isolated power supply altronics offers. We are now also putting a seperate ground on the power supply cases.

[griffonsystems 0]

it is flipping thru the pic when the lcd is attached - i had an lcd that had the bnc input that i used first then i went with a bnc to vga converter to a reg 15"lcd monitor, total crap device and that gave me the same problem but with that little 12in tv using the composite in all is good

 

there is nothing on the picture with the tube tv connected with the mux so i dont think its a ground loop issue but...

[Lolo Wolf 0]

are you looping? Is the added lcd direct to quad dedicated and then you move signal to DVR in remote location? Or are you just testing pic without interuption direct from quad to monitor (lcd) and getting poor results (noise) check the hi-Z switch on the quad if you have one- also - check to make sure you are at 1 volt peak-to-peak delivered to the quad if you suspect a voltage issue I would revisit the paths, terminations and quality of your RG (coax)

[griffonsystems 0]

i am looping out of the quad and back to the dvr

 

i did switch to hiz with no change

 

coax is good west penn wire

[Lolo Wolf 0]

Hello Griffon, after revisiting all your paths and they are solid (coax-pwr-terminations ) May very well be as Scorpion described.... however Ive had LCDs hit or miss with quality yet my CRT service monitor was clean.... had a situation where tried 3 highend Viewsonics on a set up all were poor with added noise and bad ringing in a last ditch attempt tried a cheaper Kenmark off the wall had layin around-19 lcd HDTV-TV tuner built in -used the comp in for monitor out of a VAC brick DA and pic cleaned to norm....go figure? Curious is the Quad and monitor powered from the trailer AC is the trailer on its own service or does it share the same feed from the main building maybe by way of a subpanel? Did you try going direct to monitor (LCD) at the trailer bypass the Quad with a individual cam input....if so do you still get noise?

[griffonsystems 0]

trailer is plugged into the main building i believe - 90% sure on this one

 

with the quad plugged in with no monitor no noise going back to the dvr, with a monitor noise unless its a crt then fine

 

i think i plugged a cam in to the monitor and i had noise but id have to recheck this

[Lolo Wolf 0]

Ok, reason asking bout the direct to monitor (LCD) bypass Quad with a cam input trying to see if you can perhaps isolate the disturbance to the quad output...other things to consider on the quad are there two outputs? (1-VCR 2-monitor) if you have two try both (swap) and see if there is a difference what kind of out is it BNC-Comp etc..are you looping back to DVR with individual outs or through the monitor out (quad) then controlling the channel feed? If you dont get dirt at the lcd direct from cam Sounds like your problem is somewhere from the quad output something within the termination of the connection to the LCD or on the LCD itself at the plug point. Are you just using the quad as a hardware device to monitor at the remote location or is it for a way to feed a one channel DVR? Sorry for all the questions but aside from actual hardware issues often the actual connects and their paths lead to a solution. Do you have access to a differnt LCD if so see if that behaves the same if it does then there is something going on in the feed (adapter-etc) LCD being inputed with BNC? revisit that connection pay close attention to the LCD input.... any wiggle at the input can you enter the case at the bnc input look for any rubbing or loose connections etc. From what you describe kinda points to the LCD as the culprit for the disturbance because you are certain that all is clean untill that device is put into the path.

[Lolo Wolf 0]

One more thing....check the PS to the LCD is it a brick transformer type? If so try swapping out a different one...

[mr.surveillance 0]

Did you try a ground loop isolator as scorpion suggested?

Your monitor probably has a switch mode power supply and is allowing a small amount of AC to leak in.

[RickA 0]

Might want to look at the refresh rate of the lcd's compared to the crt.