---In Avid-L2@yahoogroups.com, <bigfish@...> wrote :
Chasing a sync issue in one bay out of 10 or more. We have it localized to some sort of ground loop that is distorting the ntsc ref black and tri-leve sync signals. If the problematic bay is the only thing connected to the AJA gen-10 all is well. As soon as any of the other sync connections shield in the machine room touch the shield of any connector on the Gen-10 the noisy kicks in and Avid loses sync lock. A tek rasterizer scope wfr-7000 will still accept the sync signal as ntsc ref and lock to it but the Nitris won't. The NitrisDX has been swapped along with the HBP card and interconnect cable. This is a bay that has worked for years and in fact after replacing a broken off bnc connector on the sync line from MCR last year there was nothing like the noise I see in 2 field mode on a Tek 1750.
If you compare a good sync signal on a WFR-7000 with the bad sync signal on a WFR-7000, do you only see a difference between the two when looking at both fields?
All the power is tech power with isolated grounds. I can only guess something changed in the machine room or the edit bay that is causing the hum/distortion on the black signal to be to much for NitrisDX to lock to.
I'm adding ground loops to a close number two to the things I hate most right after fonts. Could additional equipment added in MCR somehow unbalance the isolated tech power that comes from several 20 amp isolated ground circuits to the racks and raise the isolated ground to create an issue.
First, a point about terminology. Any company who claims their power is balanced (ahem, Furman) is not really telling the truth. The power is symmetrical, not balanced. Symmetrical power involves having 60V on each leg relative to ground. Conversely, the regular power you have otherwise is 120V on one leg, with the second leg at 0V, and the third pin is ground/safety.
I know this is a lot like herding cats but figure this group might have some of their own experiences that might shed some light. I have seen at my regular gig an intermittent hum pop on and off on my online bay sync signal, that I post about here, come and go and now it's gone after I replaced the batteries in a UPS and the engineer replaced some in a few other ups units. I'm assuming that had something to do with it because those aging battery units would kick into battery mode when the power hadn't even gone out for some reason and I think that was contributing to the sync issue I was having. I have been told some of the ups units in this machine room have been serviced or replaced in the recent past so maybe there's something there. I'm thinking of trying my video humbucking isolation transformer if I can find it, but that didn't resolve anything at my regular gig so I'm not holding my breath.
A humbucker might help if the hum is at 60Hz. If you connect the sync signal to a composite video input, do you see a rolling bar from bottom to top that takes about 17 seconds to cycle off of the display?
Next maybe 3 to 2 ground lifters on the power cords to tech power in the edit bay.
Please don't do this. It's not safe.
Then maybe start turning off equipment in the bay and or machine room to see if there is any effect on the noise.
This would be the safer way to troubleshoot. Start with as little equipment as possible and figure out at which point the hum returns.
The one thing I haven't had a chance to do is look at the black ref signal in the other bays that are not experiencing the sync issue.
This would be good for comparison purposes.
So someone be my Ground Loop Fairy. If I leave a tweaker under my pillow will you come by and make this problem go away? I won't even expect a quarter. ;-)
I live too far away to be your Ground Loop Fairy. Good luck!
__._,_.___
Posted by: jonathansabrams@yahoo.com
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a New Topic | • | Messages in this topic (4) |
.
__,_._,___
No comments:
Post a Comment