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In Reply to: TV is leaking power! posted by The Sound Guy on February 25, 2007 at 20:32:16:
<< I brushed my chin on my receiver and got a mild tinge. >>This can definitely indicate a potential problem that should be investigated further.
<< I got out my multimeter and pinching one probe with my fingers and the other on the receiver's chassis >>
This is not a very meaningful or repeatable measurement. The normal way to measure is between the chassis and an AC safety ground. If your house is newer than about 1960, it should have 3-prong grounded outlets. Use the large "D" shaped receptacle as the ground connection. You will have to put the probe in at an angle to ensure that is touching the metal contact inside.
If none of the equipment is grounded (either because it all uses 2-prong power cords or because your house is old enough to not have grounded outlets), then it is not at all unusual to see 9 VAC between chassis and ground.
A good multimeter has 10 megohm input impedance, a cheaper one will have 1 megohm, and older analog meters may have 100 kohm. You can use Ohm's Law to calculate the leakage current. For example if you have 9 VAC and a 10 meg meter, the leakage current will be 9 / 10,000,000 or 0.9 microamps. This is not necessarily a problem.
<< The TV is old >>
How old is "old"? Are you talking a tube-type B&W set from the '60s, or what?
Follow Ups:
As suggested and with the input from "Bob in Alberta", I did new tests using the electrical outlet ground and the composite video terminal. (The TV case is plastic and so cannot check any where else). Here are the readings:
TV off, no cable: 0-0.1V
TV standby, no cable: 12V
TV on, no cable: 12V
TV off, cable: 2.0V
TV standby, cable: 8.8V
TV on, cable: 8.8VApparently the cable connection is sinking around 3V.
The TV is Sharp 20R-M10.
Any further insights?
I got this idea of measurement from one of Chesky's newsletter which talks about finding the correct power polarity for equipment.
http://www.chesky.com/core/body_librarydetails.cfm?newsid=156
I think the results are fairly repeatable but I will try again using the electrical ground. Yes I have grounded outlets but all my AV equipment do not use the ground. Do you think it is helpful to manually ground the chassis to electrical ground if it doesn't generate ground loops?I use a digital multimeter and I can check if the impedance is indicated. As mentioned in my reply to Al Sekela, last week I was testing a Harmon Kardon (demo unit) surround receiver but after one day of use it started shutting off. I'm not sure if the TV fried it. But the more probable reason is that the HK's cooling fan didn't work because on the first day it was running very hot and I could never hear the fan run.
The TV is a Sharp color TV, probably less than 10 years. It has remote and is multi-system capable. It is supplied by the owner of the house which I am renting.
It was not designed to be grounded, and doing so could cause a problem. As Charles Hansen said, if your meter is one with high input impedance, the voltages may not be abnormal for this type of device. However, I'd still worry about the fact that you felt the voltage through accidental contact with it.Are any of your audio components grounded to the AC safety-earth? If so, this leakage could possibly cause damage, and certainly is affecting your audio quality.
OK thanks, I won't try grounding it and create more problems. No none of my other audio equipment are grounded. I'll have to consciously keep turning off the TV (not standby) immediately after use.
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