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Author Topic: New AV panel with ground path back to orginal building AC panel.  (Read 4660 times)

Nicholas Bailey

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #10 on: December 22, 2016, 06:41:58 am »

Thanks for all the replys guys!

I worked late and did not check the post last night.

Video path is LAPTOP > EXTRON SW 4 4K > EXTRON AUDIO DE-EMBEDDER 4K > EXTRON DA4 4k HDMI DA > CABLES TO GO HDMI POWER INJECTOR > WEST PENN 75 foot fiber HDMI > Panasonic Projector.

Resolution is limited to 720p on this path because of the churchs cheap laptop.  We have a Clickshare set at 1080p on input 2, and it also shows same issue.

Yesterday I did pull the old outlet off of he stucture that projector was mounted to and that did help some.

One think that I learned is this panasonic projectors AV connectors show a 1 ohm connection to the actual Chief projector mount.

We also got all of my 4 new outlets on the same phase as well.

What I still cannot explain is this back stage I have a QSC low power monitor amp and a K-Array powered 12 inch sub.

When the power sequencer powers up those two devices by triggering a Lowell RPC1 the video on projector will flash to black for a second, but the reshow the image.

If I run a extension cord from the sound booth to that location the problem disappears.

I know now that the video signal is being dropped in the Extron hdmi DA.  If I take my Sencore generator to the actual fiber cable connected to the projector it is solid.  If my path is SENCORE > DA > Fiber cable > PROJECTOR, it will make it flash with all AC back connected to the correct locations.

I am going back today with a new DA and a ground impedance meter and see what I can find out.

I can also make it fail some times when I run the projection screen up and down.

I have learned a ton reading this message board.


Nick Bailey
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Keith Broughton

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #11 on: December 22, 2016, 06:51:45 am »

If you removed the old receptacle from the structure, the new one is still connected to building steel, as is the projector frame.
Iso the NEW receptacle, as suggested earlier, AND iso the projector mounting bracket from the steel.
This way, the projector is grounded to the AV panel only.
Still, seems odd this would be a problem of grounding when using fibre but this kind of trouble shooting is taking one step at a time.
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Cailen Waddell

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #12 on: December 22, 2016, 07:39:02 am »

Is it possible you have a bad distribution amp?  Or that there are hdcp issues causing the DA to resync?

I'm not negating what sounds like a weird power issue contributing, but it also sounds like behavior for a loose/bad hdmi connection....  ugh I hate hdmi....   

Another thought:
I would be interested to know are there big power dips when you run the screen or turn on the qsc sub?   I'm wondering if a less than solid connection in the building wiring (or even on the pole) is causing a power dip that the DA is especially susceptible to?   


Sent from my iPhone using Tapatalk
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Stephen Swaffer

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #13 on: December 22, 2016, 11:16:51 am »

In general, if this were a new sub-panel, could it be installed without a fourth "ground" wire and still pass inspection (not be a code violation)? I know that this sort of thing must have been common in pre 1960's wiring, but by the time I was reading and using my first NEC code book in 1978, that lack of a dedicated EGC wire was a code violation, at least in the industrial environment I was working in. But I really didn't work on residential wiring at the time, so maybe I missed something.

I've found ground loop currents in a Texas church and quickly discovered that the metallic conduit itself was the only EGC and apparently to code when it was installed perhaps 15 years ago. Don't know if that was a county or city thing, but the electricians there said it was common wiring practice in all the commercial buildings in the area.

I guess the adage "Assume Nothing" should be written on every electrical panel.  ;)

I doubt it would pass inspection without 4 wires--- assuming there was an inspection 😀. I may sound cynical, but having 15 years experience as an electrical contractor, my cynicism is solidly grounded in experience.

Strictly by the NEC, EMT can be an EGC-the stick of emt in the middle of a run has to be bonded- where is its EGC?  But there are conditions-no concentric ko's, etc. probably shouldnt swerve too far though.

Where does the monitor amp and K sub get their power? Could there be a bootleg ground allowing a normal power on spike to be transferred to/through a building ground?
« Last Edit: December 22, 2016, 11:23:37 am by Stephen Swaffer »
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Steve Swaffer

Mike Sokol

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #14 on: December 22, 2016, 02:53:32 pm »

Where does the monitor amp and K sub get their power? Could there be a bootleg ground allowing a normal power on spike to be transferred to/through a building ground?
Yep, a bootleg ground can indeed inject normal neutral currents into the EGC path and create all sorts of trouble, especially when gear draws a big current pulse on startup.

And I've seen a similar effect "popping noise in a sound system" when all the receptacles on a branch circuit were bonded together, but the EGC wire never made it to the service panel and wasn't bonded to neutral at all. So any single piece of gear could inject a big voltage spike into the grounds of everything plugged into that branch circuit.

Three light outlet testers are just about useless for identifying proper grounds. What are you using for a ground impedance tester?
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Frank DeWitt

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #15 on: December 22, 2016, 06:21:47 pm »


What I still cannot explain is this back stage I have a QSC low power monitor amp and a K-Array powered 12 inch sub.

When the power sequencer powers up those two devices by triggering a Lowell RPC1 the video on projector will flash to black for a second, but the reshow the image.

If I run a extension cord from the sound booth to that location the problem disappears.

Nick Bailey

I had a LED display (TV) that would flash to black for a second, but the reshow the image when a florescent light in the room behind it was turned OFF.  I wanted that TV and the CAT-5 to HDMI converter that feeds it on the same SurgeX power as the sound system and other TVs anyway so I ran new power. That fixed it.  I never did find out what caused it.
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Mike Sokol

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #16 on: December 22, 2016, 06:38:58 pm »

I had a LED display (TV) that would flash to black for a second, but the reshow the image when a florescent light in the room behind it was turned OFF.  I wanted that TV and the CAT-5 to HDMI converter that feeds it on the same SurgeX power as the sound system and other TVs anyway so I ran new power. That fixed it.  I never did find out what caused it.

Florescent lights with old-school ballasts will create a big voltage spike when turned off. This is due to the magnetic flux field collapsing, just like a relay coil. I know from personal measurement that this spike can reach 10 times the incoming voltage, so if the switch is tuned off at the peak of the 60 Hz waveform, you could create a spike reaching 1,000 volts or more. And it has a very fast rise-time, so that spike can sneak into all sorts of interconnected gear. 
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Mike Sokol
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Frank DeWitt

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #17 on: December 22, 2016, 06:55:18 pm »

Florescent lights with old-school ballasts will create a big voltage spike when turned off. This is due to the magnetic flux field collapsing, just like a relay coil. I know from personal measurement that this spike can reach 10 times the incoming voltage, so if the switch is tuned off at the peak of the 60 Hz waveform, you could create a spike reaching 1,000 volts or more. And it has a very fast rise-time, so that spike can sneak into all sorts of interconnected gear.

That ex planes it.  I am glad I put it on the surge-X circuit.  If I run into it again, it is a good excuse to switch to LED
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Nicholas Bailey

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #18 on: December 23, 2016, 07:36:02 am »

Thanks Again for all the help.

All the AC outlets were in spec.  I will shoot a pic of the vintage tool my boss brought me later.

I swapped out the HDMI DA and the problem still present.

I then found that Fiber connected to laptop would flash about 1 out of 5 times.

Move to the projector...  short cable and putting the DA up in the balcony was solid.

I then swapped in a 75 foot pro Extron hdmi cable and required Extron EQ.  That made the system solid.

The AC may have been a factor in why the fiber cable was giving me such trouble, I dont have to know why.

My though was the spick of the rpc1 tripping on the 10 foot run from the panel was causing the light source of the hdmi cable to drop momentary or get out of time.  Powering from the booth from a 100 foot extension cord reduced the spick.

I never was able to read move than a 3 volts from MIN to MAX on my fluke.


Nick



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Mike Sokol

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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #19 on: December 23, 2016, 08:40:50 am »

I never was able to read move than a 3 volts from MIN to MAX on my fluke.

If you're referring to the voltage spike, a standard DMM will never be able to read it properly since it will be only milliseconds long, if that much. You'll need a digital storage scope set to trigger & save just above the normal AC voltage levels. Then you can catch and measure the voltage spike.
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Mike Sokol
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Re: New AV panel with ground path back to orginal building AC panel.
« Reply #19 on: December 23, 2016, 08:40:50 am »


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