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Lectro R1a Damage on Camera


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I have a novel situation and am curious if anyone else has experienced anything like this. It's a long post, so I apologize in advance.

 

I often use 3 Lectro R1a's for camera scratch audio, so they can run off the same transmitter as the IFBs. I converted them to external power running off the camera, using Lectro 9V battery eliminators, P-tap cables, and a milled hole for the power connector. I have a 3.5mm TRS to XLR (tip to pin 2, pin 3 float, pin 1 GND) for audio. This setup has been in regular use, with no issues, for 4 years.

 

Two weeks ago, all three R1a's failed, one after another, on one particular camera. The specifics of the damage are being evaluated by Lectro now, but the green light is still on, just no audio output.

 

The first obvious question is why did it take damaging 3 R1a's to learn my lesson?  Fair question. After using this setup for a long time, I thought nothing of the first unit not working and, being in a hurry, set it aside and put a second unit on the camera. It stopped working right away. Now I was suspicious, so before potentially damaging a 3rd R1a, I double checked that:

 

- No +48 was going into the R1a (Camera in line level mode. Still, I tested both pins 2 and 3 to ground with a meter and no aberrant  +48VDC)

- All 9VDC batt eliminators were outputting correct voltage/polarity from the suspect camera and P-tap cable.

- No obvious "in-rush" current-type voltage increase at the 9VDC terminals when powering the camera up.

 

After that troubleshooting, I took the entire R1a and cabling setup from the other camera that was working fine. I put it on this camera. It failed immediately. Lesson learned. 3 dead R1a's.

 

Finally, my questions to you all:

 

1) Both the "good" camera and the "bad" camera had identical Teradek transmitters.  Has anyone ever seen an R1a be damaged by Teradek RF? Either by close range RF transmission, or by sharing a DC/RF ground plane?

 

2) Anything I'm missing in my troubleshooting outlined above?

 

Brian

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Man, if that Teradek is killing your R1A then why isn't it killing the onboard extra monitors, TC devices, focus units etc, not to mention the operator and maybe the electronics of a Steadi rig?    Are you sure all the grounding in your rig is good, like you really aren't getting DC into the ground of the RX?   What happens when you try an RX with those cameras that is running off its own internal battery?

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I'm extrapolating from what little I know, but since witnessing something kinda maybe similar, and since cheap(ish) d-tap/p-tap camera batts are increasingly part of my little world, I've learned a bit that *might* be relevant. Short version: D-Tap/P-Tap cables and ports aren't optimally designed or made...and different brands of connectors and ports don't necessarily connect cleanly...and all this can cause shorts. I have no idea if this is what you're dealing with Brian. Best of luck.

 

If your were powering your R1a units with the same battery used to run the camera, maybe the p-tap cable shorted the R1a units? I'm pretty sure something like that happened on to a C300 a few years ago on a job (not my camera or department, "luckily," but all around bummer). So the camera battery that powered the camera had a d-tap port that was used to power a small monitor....and when plugging in the d-tap cable, the SDI BNC port on the C300 went down. The camera had to go back to Canon for repair. That's the only incident I've witnessed, but I've heard of people having the same problem with d-tap/p-tap connectors powering external monitors leading to fried camera SDI or HDMI ports on a few brands of camera (paraphrase: "This all worked fine for months...and the all of a sudden..."). Arri and Red both warn about stuff like this. And while I haven't heard of issues with RX, maybe...

 

Apparently, when connecting a d-tap/p-tap cable to power, sometimes the d-tap/p-tap positive pin connects before the negative (especially on crappy or damaged connectors), and if the same battery is powering both the camera and an external peripheral connected through a BNC, HDMI, and perhaps audio port, then that port is used to close the circuit and sometimes fry the port (and perhaps peripheral). Not sure that's clear. I'll embed a couple links that explain things succinctly.

 

So when using a single battery power to power both a camera (directly) and a peripheral (monitor, rx, etc) via d-tap/p-tap, first connect the battery to the camera, then connect the d-tap cable to the peripheral. And only then connect the audio (or monitor) cable to the camera and peripheral. When disconnecting, disconnect the audio/monitor cable before unplugging the d-tap cable. Or power your RX/monitor with their own batteries...

 

Here's a three-page PDF from Arri titled "Preventing Damage to SDI outputs"

https://www.arri.com/resource/blob/194752/d3093e6af632150787ec95d176a39958/download-technical-information-data.pdf

 

Red has similar info:

https://support.red.com/hc/en-us/articles/360057166453-Preventing-Damage-to-SDI-Outputs

 

Here's a one-minute video from Arri explaining the SDI short problem (google doesn't show the video on YouTube, so this might not embed):

https://www.arri.com/resource/blob/195968/994529ee419abe1e2ca0dfbf95c4b4e1/marc-shipman-mueller-data.mp4

 

HTH!

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- 24V or even 48V system? I guess there are such batteries and cameras. Same D-Tap, other voltage. Dangerous and not good anyway.

- Jim's approach: What if the ground (-) of the power supply was faulty? So (+) was fed correctly into your receiver, but all ground connection went through your audio connection (shield) and so to say through the audio stage. That would explain why audio is damaged now but still an led burning.

 

Well, whatever happened: What a mess, I feel with you

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I don't like powering stuff off cameras--you can too easily get blamed for all sorts of issues that aren't your fault if the AC gets panicy.  I understand that some ENG type rigs need to power slot RX as standard operating procedure, but that kind of powering is way more reliable and buttoned up than trying plug in via wires.  I did this for awhile with some Moze mic pres on Alexa Minis, and was never happy about it.  We prefer to use gear that has its own battery and just live with the extra work maintaining them.  I guess if you worked with the same cameras all the time, or on a really long job with time to experiment you could come up with something good, but in the world of short gigs with new cameras and different ACs every time getting into the camera dept's powering thing is something I want to avoid.

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Continuing from Jim's post: the case of the R1a is "ground" for audio purposes, but is at half the DC power supply voltage when 9volt battery powered (Lectro ISOVOLT battery eliminators may have a different outcome). There is a 4-5 volt difference between the Ra1 case and XLR pin1, meaning that if the XLR is connected to the camera, and the R1a case also makes contact with the metal parts of the camera, then a low impedance DC path exists ... a short circuit / fault. I don't know the specifics of what happens with the R1a in this situation, but I have had R1 receivers shut down from excess current & heating on the rx output amplifier. The solution was to fit an electrolytic capacitor into the XLR shield / pin 1 for DC isolation

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6 hours ago, noises1 said:

The solution was to fit an electrolytic capacitor into the XLR shield / pin 1 for DC isolation

COOL.  SUPER COOL.  Can you expand on this part?  Especially how you found the cap value.  I am interested in this whole short process. 

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Did the failure occur when using the 9 volt battery eliminator or the ISO9VOLT?

If using the original battery eliminator, the ground connection for the IFBR1A audio output would be at a positive DC voltage when compared to the negative connection for the DC power.

If the audio input ground and the DC supply ground for the camera were common, this could cause the output IC failure noted in our repair department.

 

 

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