Funny problem - any ideas ?

[watchdog]

Went to look at a 32 camera ( 2x16 ) PC based DVR system today for the bloke (STI) who somehow managed to get the job of installing & maintaining it a couple of years ago. Now this bloke is not technically inclined to say the least so he would have had someone else install it & certainly a parade of idiots maintaining it. List of problems -
Move ANY cable at the back of the rack & it is like a Keno draw as to which cameras will stop working
The 8 way cable from the capture card seems to have an internittent (probably from the weight of the 8 coaxes hanging off it
One PC continually needs re-booting & the other one continuall freezes

Anyway the story was that five cameras were not working & if they were not fixed by the end of the week he was going to lose the site. The techs he had previously used had been in & out for weeks & couldn't find the problem & were now either refusing to go or simply not answering the phone. So now he had somehow got onto me (& I had answered the phone) & I'm a soft touch for a sob story.

Camera 1 - Up the ladder for a look & discover no power. Coming out of the conduit is a second fig 8 cable . Stick the meter on & what do you know - 24V ac, exactly the voltage required for the camera - how lucky.

Camera 2 - Up the ladder & no power. Closer inspection shows the telltale green stain where it comes out the conduit. Cut it off before that point , stick the meter on & guess what ? 24 V ac
Two fixed in an hour , the Man just about had tears in his eyes.

Camera 3 & Camera 4 are almost side by side & a poke around with the meter & you guessed it - no power. Stick my head up the manhole & there are two fig 8 cables, one connected to nothing but has 24V ac on it & the other one connected to both cameras 3 & 4 but with nothing on it. Swap them round & hey presto , Cams 3 & 4 are good to go. Four down & the Man was getting ready to nominate me for a sainthood.

Camera 5 - Detatched building , cable in U/G conduit. Some clown has mounted a very large CRT TV on a suspended shelf in the corner where the camera is. Get the TV shifted , pull the dome down & you guessed it - no power. BUT not like the other no powers , this one had no power cable connected to it at all. Hop up in the ceiling to find it & it's simply not there. Trace it back to where the U/G conduit enters the building & it is simply not there. I don't think this one has ever worked. I think the idea was to power it locally bit no one got around to it.


Now the question. One camera has a perfect pic with the test monitor on the camera. But the picture displayed on the DVR is tearing & the frame bar is about 1/3 the way down the screen. When I plug the coax at the DVR end into the test monitor I get NO video at all. Plug it back into the DVR & you get the crappy picture. I can only assume it is a sig level problem for it to work on the DVR but not the test monitor. What do you think ?

[CCTVguru]

I would bet it is an earth loop.

First, nothing to do with earth loops but re terminate the BNC's at the back of the DVR if they are loosing signal when you move them. It is likely if the install is that bad, there are Loose strands of copper that may be shorting to the center core or the core is not crimped into the pin correctly.


Now get a earth loop isolator (about $80) and plug it in line with the coax in question to see if the fault goes away.

PS - is the test monitor a battery powered or 240v? I am guessing battery as this will lift the earth loop. The camera that works on the DVR but not the monitor may not have the shield connected but the earth is coming from another coax while connected to the DVR

[watchdog]

I would bet it is an earth loop.

First, nothing to do with earth loops but re terminate the BNC's at the back of the DVR if they are loosing signal when you move them. It is likely if the install is that bad, there are Loose strands of copper that may be shorting to the center core or the core is not crimped into the pin correctly.

This problem seems to be the flying leads on the video card. Plug any one lead into the test monitor & the picture is pretty solid.

QUOTE=CCTVguru;355293]
Now get a earth loop isolator (about $80) and plug it in line with the coax in question to see if the fault goes away.

PS - is the test monitor a battery powered or 240v? I am guessing battery as this will lift the earth loop. The camera that works on the DVR but not the monitor may not have the shield connected but the earth is coming from another coax while connected to the DVR[/QUOTE]

I've had plenty of experience with earth loops in audio stuff ( PA systems etc) but not on CCTV systems ( my jobs are done good ) So are we talking here a "multiple earth" where an unbalanced signal is deriving an earth from two sources that are slightly different potential as in PA gear. OR are we talking "foreign earth" where the signal earth is missing & the earth is derived from another source. eg. an RG59 in line joiner earthing to the metal building frame.

[Drift]

This problem seems to be the flying leads on the video card. Plug any one lead into the test monitor & the picture is pretty solid.

QUOTE=CCTVguru;355293]
Now get a earth loop isolator (about $80) and plug it in line with the coax in question to see if the fault goes away.

PS - is the test monitor a battery powered or 240v? I am guessing battery as this will lift the earth loop. The camera that works on the DVR but not the monitor may not have the shield connected but the earth is coming from another coax while connected to the DVR

I've had plenty of experience with earth loops in audio stuff ( PA systems etc) but not on CCTV systems ( my jobs are done good ) So are we talking here a "multiple earth" where an unbalanced signal is deriving an earth from two sources that are slightly different potential as in PA gear. OR are we talking "foreign earth" where the signal earth is missing & the earth is derived from another source. eg. an RG59 in line joiner earthing to the metal building frame.[/QUOTE]

Typically multiple earths. A ground loop isolator as already mentioned will likely solve the issue.

[watchdog]

I've had plenty of experience with earth loops in audio stuff ( PA systems etc) but not on CCTV systems ( my jobs are done good ) So are we talking here a "multiple earth" where an unbalanced signal is deriving an earth from two sources that are slightly different potential as in PA gear. OR are we talking "foreign earth" where the signal earth is missing & the earth is derived from another source. eg. an RG59 in line joiner earthing to the metal building frame.

Typically multiple earths. A ground loop isolator as already mentioned will likely solve the issue.[/QUOTE]

This just breaks the coax earth I assume ?

[Drift]

This just breaks the coax earth I assume ?

It isolates both the signal and ground with a 1:1 isolation transformer.

[Privatteer]

Other possibility is a low signal from a excessively long run/high loss join.
I'm guessing your test monitor might be a LCD? I've seen it couple times where a bad signal just refuses to show on my test monitor but shows on the DVR/full size screen.

I would be concerned that the 4 cameras had been moved off one powersupply for a reason, ie underrated and that elsewhere you have a dead supply on the other fig8s.

[watchdog]

The first thing I thought of was low signal level. The signal will be regenerated in the A/D quantising process in the DVR & so will be of a good level but shithouse quality as shown by the DVR. The test monitor however is just expected to display the signal which it cannot do due to the low level. I don't think it's the length of run as this is one of the two cameras side by side & the other one is fine. The power supplies are questionable as well.

Should have more answers by the end of the day

[watchdog]

All the riddles are solved. The camera with the suspected low sig level turned out to be a stuffed BNC-BNC joiner. The power cable for the camera in the detatched building was traced. where the U/G conduit enters the detatched building there were two Cat 5 , a coax & a brown/white fig 8. Trace the fig 8 & find it is joined to a Blue/white fig8 that then runs to the audio rack. Go to the main building where the conduit leaves & trace the brown/white fig 8 & it goes to a sky/fox receiver rack. This is at a racecourse by the way. So it looks like whoever did the PA/broadcast/sky wiring needed a fig 8 to the detached building ( a function centre at the track) & stole the cameras power cable. This would explain the 6" of brown/white fig8 on the back of the camera & the cut cable at camera 3&4.
I believe the witch hunt has begun.