John Brawley wrote:I think David Green here on this thread did some great detective work on an earlier thread that also seemed to indicate bad internal wiring practice in some accessories...I'm hoping he'll post to it. Is that still your view David ?
Thanks John.
I posted on a thread here last year regarding this issue.
I spent an afternoon looking into this along with the SDI buffer IC design (one of my hats is an electronics engineer).
The V-Mount plate shown in the thread uses isolated grounds, which may cause ground connection contact bounce when connecting the SDI cable if the camera and EVF are using the two independent power sources on the plate.
This is why I mentioned in my post above about making sure that both devices are powered off before fiddling with the cabling.
The typical SDI buffer IC specification has a design that
should be able to sink the contact bounce, so this is more of a preventative measure.
I would still personally train people to not fiddle with the cables while the units are powered on.
What I was surprised to find is that whoever in the industry designed the SDI interface only designed it with ±5kV or less ESD protection on the I/O buffer IC.
This is insufficient for outward-facing interfaces, they should always be ±15kV ESD protection or higher.
This means that if you are carrying even a small static charge, you can fry the SDI buffer IC if you touch near the center contact and cause a discharge. 5kV is so low that you most likely won't even feel it, but you will notice when your SDI no longer puts out any signal.
Many of the professional rack-mount multi-SDI interfaces have warning stickers on them regarding the static sensitivity of the SDI interface.
So any SDI static sensitivity is
not the fault of BMD or any of the monitor manufacturers, they will be using the ICs supplied by a semiconductor manufacturer that is designed to the SDI industry specification.
Please note that I have not seen any BMD camera schematics and I am assuming that BMD and other SDI-equipped device manufacturers are not using off-chip ESD protection devices such as TI TPD4S/8S HSVI SMDs.
Assuming that this is in fact what is damaging the BMD camera SDI output for those people posting here, and since the ESD protection is imho insufficient, I would expect to see a small number (1 in 5,000) of people who are unlucky enough to be frying their camera.
This issue will appear to be highly random across camera users, since ESD discharge issues are also quite random.
Note that when I was looking into this, I found similar posts regarding dead SDI outputs on other camera manufacturer forums, such as Canon, etc. They will be using the same/similar SDI buffer ICs with the inherent under-rated ESD protection.
I
always discharge myself when handling the SSD or SDI on my BMD camera.
It is usually as easy as touching any large metal object next to you such as a metal table or metal stand.
These same static prevention measures should be followed when handling the SSD drive.
SSD drives and the SATA interface also do not have high ESD protection.
SATA is not an outward-facing interface. SATA, mSATA, etc. are only around ±4kV ESD.
When you open your SSD drive package, keep the translucent antistatic protection bag that the drive came in, and always use it for transport and storage of the drive. Note that some blister packaged drives do not include the protection bag unfortunately.
Use care and try to never touch the drive contacts.
On computer motherboards, where you typically see SATA interfaces and SSD drives, only the outward-facing interfaces are high ESD protected, such as the Serial, Parallel, Ethernet, USB, eSATA, etc.
CPU, memory, SATA, etc., require static prevention measures when handling them.
David R. Green - Demenzun Media Inc. - Author Composer Filmmaker Programmer