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435 - Strange Video Assist Problem


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#1 grant mcphee

grant mcphee
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Posted 13 November 2007 - 06:38 AM

Hello,

I was video assist on a commercial recently and encountered a strange problem that I couldn't/can't figure out.

We were using a 435 with a pal video assist, 21" monitor for client and 9" dvcam combi to record. A fairly standard package for low budget commercials and something I'm pretty familiar with.

At the start of the day I connected everything up - Camera to DV Combi and daisy chained DV Combi to Client monitor using the video out. I used a 50' cable drum for each monitor with a 5' short bnc to connect. Camera was switched on and each monitor had a picture. Nothing odd, I'd done this hundreds of times before.

The focus puller was having a problem with the frame markings. He'd not used the 435 for a while so until he worked out how to sort it he asked if he could t-piece out of my bnc (he was using the one with the info, I was using the clean one).

He was using the transvideo 5" so I quickly t-pieced up his monitor out of the other bnc. He got the image, as expected. I quickly checked the dvcombi which also had a picture. As the client monitor was daisy chained from this I did not check it - it was working fine before. A couple of minutes later I got a shout that the client monitor had gone down.

As the only new piece of equipment used was the t-piece and on board monitor I tried changing that t-piece with no luck. I quickly tried changing the bnc to the client monitor - still no picture. We decided to switch the on board monitor back to it's own bnc as it had been at the start of the day - everything worked again. we decided to keep this set-up as there was not enough time to find out what was happening - i assumed it would be something to do with the dvcam, possibly some kind of resistance issue - though I always thought that it's output was amplified. Termination problems usually still give a picture.



Later on the dop asked if he could have a monitor for himself. I daisychained this into the start - camera, 9" monitor, dvcam, client monitor. As before, the client monitor had no picture. I tried a few variations - t-piecing the output of the camera so the 9" had a seperate bnc - I would have expected the client monitor not to have a picture but on top of that the dvcam combi did not have one either. It seemed to be something with the video assist. Swapping the output of the t-piece over had no effect (always a picture to the 9").

In the end I t-pieced the output of the onboard to the 9" and kept the dvcam/client with it's own output - though not great for the grip having two bnc's trailing out of the camera.

Any ideas? I'm not an engineer so don't have a great knowledge of what's going on inside. But like I mentioned, I've done this plenty times without anything like this happening. Am I doing something odd and have just been getting away with it? I don't think it's a termination problem as the sony monitors are auto terminating, and at some point I did try using external terminators in case the internal sony ones had packed up. It does suggest a resistance problem as the monitor which is furthest away is the one having the problem. Is it the output of the camera? On the other hand, I've used a 435 with well over 200' of bnc and had no problems.

Any suggestions appreciated. I might be using the same camera again on a more complicated set-up so wan't to know if it's something I should get the rental house to look over.

thanks
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#2 Hal Smith

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Posted 13 November 2007 - 08:48 AM

I was video assist on a commercial recently and encountered a strange problem that I couldn't/can't figure out.

A quick thought (I'm out the door to a gig). It sounds like you might have had more than one termination. You need one term at the end of the daisy chain. If you bridge a monitor off with a tee make certain the added monitor is non-terminated - it should be in bridge mode. If I had to guess, the Sony monitor autotermination is creating the problem. Can you turn it off and use a 75 ohm bnc terminator instead?
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