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With nothing hooked up to the Mitsu and power on, I put a DMM between the TV "F" or rca's and a house ground I get 57 VAC@60Hz. Switch polarity on meter - 34 VAC@60Hz
I have been tracing a ground loop hum coming from my Mitsu 55857. When any RCA's from a grounded source are hooked up one at a time the voltage drops until enough grounded RCA's are hooked up, reducing to 0 volts????
Only the Mitsubishi - 1 of 4 TV all on the same splitter, is putting out VAC.
The CATV cable will produce the same effects as the house ground. It appears the CATV is clean, as I checked it at the grounding block.
I have been butting heads with the mitsu tech for days. He claims it's a ground loop in the CATV - I say it's a floating gnd problem inside the tv or the power supply.
Any feedback would probably avoid an ulcer!
Thanks,
Mitch
Mitch
Follow Ups:
Make sure the CATV ground at the house entrance is clean and solid. Next, float the ground on all components... the system will still be grounded through all the interconnects. I researched this topic thoroughly here and I found other inmates who agree. I prefer this method to a ground isolation transformer.Using this method, you may have even better results by turning your amplifier on first, if it can be done without a thump or pop in your speakers.
Hi Wayne,While it makes sense that the system is grounded through the IC's to the CATV ground;
As for CATV ground, only as of 1999 the NEC required the CATV be grounded to the Utility ground and the ground rod closest to the Service Entrance. Before that a piece of copper tubing could have been used.
First each branch is rated for a specific current. The conductors are rated for the same current. This includes the GROUND CONDUCTOR. The purpose is to be able to carry that same rated current back to the Panel in case of a short, or excessive heat as well as to carry stray voltage back to the ground.
Second, and I know this issue has been beaten to death, but lifting a ground is dangerous for the above reason.
Try shorting even a 5 amp load (line to an IC return), say the IC is using very fine wire copper or silver, By,By to all the equipment as the breaker will NEVER trip - the wire will fry. Perhaps arc and start a fire. We don't have ARC FAULT's installed yet which MIGHT trip in this case.
THird , a power surge which will hit all devices plugged in the house, again the thin wire can't handle the voltage, current, or the heat.
Fourth, depending how each duplex rec. is wired in the branch in question, anything on that circuit can fault, sending the current from another room into the equipment as well (unless it's a dedicated branch)
So when the fire dept. comes and looks at all the grounds lifted, not only will this void all warranties and insurance policies, one could be possibly be prosecuted, depending on the amount of damage to property or person!
We all ultimately do as we think is best!
Mitch
You concerns are genuine. My power filter, which feeds my entire AV system, has a GFI and the unit itself is properly grounded through its power cord. If I found a CATV ground isolation transformer worth a darn, I could ground the system at the amplifier through the amp's power cord without hum. I share your frustration on this topic because I have never received a clear response from anyone, except in the archives here. The best I can figure, if you float the CATV ground with a MAGIC, or similar, the CATV box's ground path would still go through interconnects to get to the amp. Since I have never seen a CATV box with a grounded AC cable, I prefer to keep it grounded in accordance with the NEC and not use a CATV ground isolation transformer. Please respond as I would like to nail down this issue, even if it means I must change my setup.
Wayne,How did you make out with testing the line and load side for voltage?
You got voltage - I got a solution.
I plan to callJensen Transformer regarding VR-1FF to see if it will help as a precaution for any future additions to the system. There might be some frequencies not evident in the TV audio section but when the Surround is finally hooked up - well they will probably know!
Their white papers theory is correct. Maybe a little simplistic but nothing wrong with that!
Let me know so we can get rid of you stray voltage!Regards,
Mitch
Is your hum coming from the TV feeding back through any device that has a ground or is it coming in through the cable into the TV.
I guess one could say is it on the line or load side of the cable, Mine is on the load side of the cable
I'll get to the bottom with a solution and up to code!
BTW have you checked out Jensen Transformers?
Regards,
Mitch
Unplug the cable TV feed. If the hum goes away, you have a ground loop problem related to your cable TV. In that case, you will have to buy some kind of ground breaker to fix it. I got one for $10 or $20 from my local high end audio dealer to fix a similar problem; although, there are more expensive products available.In my case, what triggered the problem was installing a new Bryston amplifier in the system. I think I may have had a slight problem before, but installing the new component exacerbated it for some reason.
Todd
Removing the CATV does remove the hum. However adding a ground to the CATV also gets rid of the hum. IE; adding a ground to the ground of the cable ??
Why does'nt it present on all tv on the CATV line?
This is really screwy!
Thanks for your help,
Mitch
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