Thread: The SDI issues

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  1. #71  
    Senior Member Robert Hofmeyr's Avatar
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    I'm still not understanding why there would be a large potential difference between the ground of a monitor and that of the camera if they are powered independently. But if this is the case, wouldn't just connecting the two grounds sort out the problem? And if the monitor and camera are both metal and have chassis grounds, wouldn't they be connected already if the monitor is mounted on the camera?

    Edit: also, if this is the case, then the order of connection will make no difference, since the potential difference between the camera ground and monitor ground will still be there after the batteries are connected. And if the positive of the monitor battery makes contact before the ground it will not have an effect, since no circuit is formed.
    Last edited by Robert Hofmeyr; 04-18-2021 at 02:09 PM.
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  2. #72  
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    Part of the problem is that the equipment being plugged into these cameras isn't...errr...like what get's plugged into more expensive cameras. It's not the same kind of well designed consistently performing (electrically speaking) equipment as more expensive RED camera users would be using.

    People are using lesser known(for quality) accessory brands, lower cost items, commensurate with the price of the camera. Therefore, I think it's why you're also seeing more issues. Directly powering from a battery instead through power regulation.

    Cheaper, less well designed and built stuff running from direct power from a battery and no ESD protection because it messes with the spec of the port. And while in THEORY you can't short out the centre pin, I've seen poorly made SDI plugs where you could conceivably do just that when connecting if you're not careful.

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  3. #73  
    Senior Member Robert Hofmeyr's Avatar
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    Here's a summary of what we have learned if we want to avoid blowing the SDI:

    - Only use high quality 12G-SDI cables
    - Don't power your monitor via d-tap
    - Don't power your monitor from it's own battery
    - Don't connect or disconnect your monitor's power cable while an SDI cable is connected
    - Don't connect or disconnect the battery on your monitor or on your camera while an SDI cable is connected
    - Don't connect or disconnect an SDI cable while the camera is running
    - Only use high quality monitors
    - Do buy an inline SDI isolator and keep it attached to your camera

    :)

    Edit: the thing that is confusing me here is that some people are saying this is a ground loop issue (only happens when camera and monitor use same power source) and others are saying it's a differential grounding issue (only happens when camera and monitor use different power sources). This makes it very hard to protect against. It would help a lot if we knew if it is one of these issue or both of them.
    Last edited by Robert Hofmeyr; 04-21-2021 at 12:22 AM.
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  4. #74  
    Hi everyone,

    I have prepared a rather specific question and would love to get some insight from you guys if possible. (maybe this will also clear up some things for someone else?):

    So I originally I planned on using the d-tap out of a budget v-mount plate to power my komodo (when it arrives). Because of the whole d-tap safety issue discussion I'm thinking of replacing my d-tap splitter with one for lemo such the following one and also switching the d-taps on my cables out for Lemo 0B 2 pin connectors.

    https://www.bhphotovideo.com/c/produ...o_3_power.html


    Because the V-mount plate still has d-tap I'm considering to buy this safetap connector from Lentequip and replace the lemo out of the splitter with it.

    https://lentequip.com/products/safetap

    Sice there are more expensive v-mount plates with fuzes, regulators, esd and lemo from the start, I wanted to ask if this, also combined with a sdi galvanic isolator, could be a cost effective (and small) alternative to get a similar protection (like a D-Box from Wooden Camera for example). Or would I still be compromising on safety this way?
    So regarding to power damage, is there anything else that can happen to a Camera than the sdi port getting fried (which there are methods to prevent), when using budget, non regulated v-mount power? (Btw with the lemos coming out the safetab obviously I'll only connect accessories that can handle the various voltage or else I'll put a voltage converter cable there)

    Does anyone know if things like overcurrence or power spikes or something else can happen with a v-mount that can damage the cam and other accs? If so, what are those? Any stories or experiences?

    Thanks

    Also @ Robert Hofmeyr, thanks so much for your Summary above, I think this was a great idea and will help a lot of people! If you have a moment can you explain why only to use high quality monitors? (I have a cheap one :P). Does a galvanic isolator help in this regarad, also could the above mentioned safetap help maybe (by preventing power spikes while powering the monitor e.g.) ? Thx again mate ��
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  5. #75 Common ground 
    Senior Member Blair S. Paulsen's Avatar
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    Any accessory, including monitors, needs to be properly grounded and shielded internally or all bets are off. A low cost monitor that has poor image quality, but robust electrical circuits is no larger risk than a high end monitor. That said, how many monitor reviews have you read that dove into such issues...

    IAC, in terms of rigging power, the best insurance would seem to be a common ground for everything. That way, whatever causes it, power blips have somewhere safe to go. That's my plan anyway.

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  6. #76  
    As I understand things, the issue arises when the SDI cable is connected first and the positive pole of the battery, or battery connector, makes contact before the ground (negative) connector. So, the immediate conclusion is to remove the SDI cable before connecting battery power, whether it's to the camera or to the monitor.

    All this being the case, the simplest solution, as well as the cheapest, is to install an on/off switch inline with any external monitor and its power connector. As long as the switch is turned off it's not possible for the positive pole of the battery to make contact to any ground loop before the negative pole of the battery makes contact. Zacuto sells a d-Tap power connector with a built in on/off switch.

    I have a micro on/off switch on all my external Dtap power supplies. Knock on wood, but, I've never had a problem over years of use this way.
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  7. #77  
    Senior Member Robert Hofmeyr's Avatar
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    Quote Originally Posted by Bill Ravens View Post
    As I understand things, the issue arises when the SDI cable is connected first and the positive pole of the battery, or battery connector, makes contact before the ground (negative) connector. So, the immediate conclusion is to remove the SDI cable before connecting battery power, whether it's to the camera or to the monitor.

    All this being the case, the simplest solution, as well as the cheapest, is to install an on/off switch inline with any external monitor and its power connector. As long as the switch is turned off it's not possible for the positive pole of the battery to make contact to any ground loop before the negative pole of the battery makes contact. Zacuto sells a d-Tap power connector with a built in on/off switch.

    I have a micro on/off switch on all my external Dtap power supplies. Knock on wood, but, I've never had a problem over years of use this way.
    Good idea.
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  8. #78  
    Senior Member Tehben Dean's Avatar
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    Quote Originally Posted by Michael R View Post
    Thanks, Rob. There were no active swaps and the camera was powered down as we were moving from an AC-powered setup on sticks to a v-mount powered setup on gimbal. We filmed the interview (monitor working fine), powered everything down, unplugged AC, unplugged SDI, mounted the Komodo to the RS2, mounted monitor to the RS2 left handle, reconnected SDI, no signal. Tried different cables, different monitors, different batteries, everything. Never got a signal out of the SDI port again.


    Just submitted a support ticket to Red so I'll update you when we hear back.
    "..powered everything down, unplugged AC, unplugged SDI.."
    Betting it was unplugging the AC before unplugging the SDI?

    I have never burned a port but I keep everything powered off a single gold mount battery on the back of the camera using a TILTA plate. I did recently get a power cable with 2-pin LEMO to power my TVlogic but I used the p-tap beforehand and always left everything plugged in and just power the camera and monitor down before swapping batteries.

    Would be great to hear if these practices are considered safe.
    1) Powering everything off the same power source?
    2) Using 2-pin LEMO to power monitor?

    So far so good but it's a little scary hearing about this issue.
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  9. #79  
    Senior Member Robert Hofmeyr's Avatar
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    Quote Originally Posted by Amarin Spörri View Post

    Also @ Robert Hofmeyr, thanks so much for your Summary above, I think this was a great idea and will help a lot of people! If you have a moment can you explain why only to use high quality monitors? (I have a cheap one :P). Does a galvanic isolator help in this regarad, also could the above mentioned safetap help maybe (by preventing power spikes while powering the monitor e.g.) ? Thx again mate
    Hi Amarin. My list was a bit tongue-in-cheek: it would be very hard to follow all those rules, and impossible in most production environments.

    The truth is we don't seem to be entirely sure what causes the SDI to fail. If the problem is ground loops, then using a separate battery should prevent it, but it seems people powering their monitor from its own battery have also had the issue (there may be some confusion because I have also heard of BNC port issues where the inner petals in the port get bent). If the problem is more prevalent when users are powering their monitor from its own battery, then it is not a ground loop causing it, but it could be a result of the different potential of the two negatives. At this point only Red knows the number of failures and whether they are primarily from the ground loop issue or something else.

    I don't see a problem powering the Komodo via d-tap. The ground loop is formed when you connect an SDI accessory via a cable to the same power source as the camera and the positive makes contact before the ground. This is most likely to happen with a d-tap connector. Now, if your monitor is also powered by the same battery (via a d-tap splitter) there will be a small risk of a ground loop whenever you plug in the second d-tap while your SDI cable is connected. This is not a huge issue because I assume you will not be plugging and unplugging these d-taps very often, so you can just disconnect the SDI cable before plugging in your power. Alternately, plugging the camera and monitor into the splitter before plugging the splitter into the plate should also prevent the ground loop.

    I'm not sure if the safetap will prevent a ground loop - seems it's primarily for reverse polarity. Perhaps email the manufacturer and ask if output on the positive connector is prevented until the ground connector makes contact?
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  10. #80  
    Senior Member Aaron Lochert's Avatar
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    Quote Originally Posted by Amarin Spörri View Post
    Because the V-mount plate still has d-tap I'm considering to buy this safetap connector from Lentequip and replace the lemo out of the splitter with it.

    https://lentequip.com/products/safetap
    According to this article, the SafeTap doesn't actually protect against this specific fault! It protects the accessory from reverse polarity but it does not help the sensitive SDI problem.

    The SafeTap Dilema

    It was brought to my attention via a client that there is a blog on Newsshooter that claims that the SafeTap and its protection features is a viable work-around for using P-Taps in a way that will mitigate the problem described in the Arri technical advisory. Finding this claim to be dubious, I actually put a SafeTap up on my bench to test this theory myself and found that the information in the article is not accurate. A SafeTap should not be relied upon to protect against this specific problem. In fact, it can actually worsen the issue. We do not recommend using SafeTaps for hot-plugging or when coaxial lines are already connected to your camera. In fact, we do not recommend connecting the output side of a SafeTap cable, turning on any devices, or plugging in any SDI lines until the SafeTap flashes green and connects the ground line.

    For additional context, upon testing, I found that the SafeTap disconnects the ground line instead of the positive line (like a transistor). This means that if you have a stray path to ground, (a BNC shield in this case) the positive voltage line will instantly connect, defeating the SafeTap's protection features entirely. Even if the cable shield is connected to the SafeTap’s negative output terminal, the positive line will always directly connect if there is another ground connection available.
    Via https://rencherindustries.com/blogs/...n-arri-cameras
    Last edited by Aaron Lochert; 04-21-2021 at 12:22 AM.
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