I checked continuity on all the links of the coax cable for the sync signal and all is good there. Something about the shields in the machine room having a difference of potential with the shield coming back from the edit bay superimposes a some hum and other nasty distortions. I'm thinking something in the machine room changed but I would think that would effect all the bays. Oh well here kitty, kitty time to start rounding up the litter.
---In Avid-L2@yahoogroups.com, <jonathansabrams@...> wrote :
---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :
A ground loop is simply an added path to ground, which creates an antenna loop, and you get noise generated from any electrical signal in the vicinity, mostly the AC mains. You probably already know this.
John - The above text is fine.
Get a bucket of those old adapters that take a 3 prong grounded plug and allow it to be plugged into a 2 prong plug. Put those on all your gear, except for a primary component, and they all share the same ground, through the wires connecting the equipment. (better than just cutting off all the ground plugs on your power cords).
John - Please do not do what Dave wrote above! This is dangerous. Devices that have 3 prong plugs have them for a reason. What is that reason? Safety! If you lift the third prong (ground), you have just defeated the electrical safety mechanism of the device in question. For those of you thinking, "The device has a fuse", I counter withe question "Which device will die first? You or the fuse?" The answer is you.
Used to have to chase this in audio studios when they were all analog. Just put ground lift plugs on everything except a primary piece of gear, like the Switcher or Audio console. I use the ones that have polarity blades, so that I don't end up pumping full power down to ground....You'll know when that happens when the lights go out, and things go spark!
Dave - Did anyone using that equipment ever get injured from a shock? Consider yourself lucky if they did not. This is not the proper way to solve the problem you described.
You also have to make sure that nobody made bum cables (Audio XLR mostly) which swap the ground and hot leads.
John - This is true and easy enough to check with either a continuity tester or by opening the connector shell and seeing which leads are connected to which pins.
Only other thing that can cause an issue is if your have a shield loose on a video cable. Check continuity on the shields.
Dave - If the shield on a coax cable was compromised, would you have any signal at all? The circuit wouldn't be completed with a broken shield.
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