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Old 16th September 2012, 12:12 PM   #11
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I think the source of the confusion is the fact that I mentioned having mains/2 relative to earth on all grounds. I don't even know why I wrote that, it's irrelevant as it's because of a very small current passing through caps. each and every SMPS out there behaves like that because of 2 small caps going from ground to hot and cold.
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that would only explain failure if those caps were defective.

and yes, the TV ground is earthed by the coaxial TV cable going to it. it is earthed by the provider for good reason.
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Old 27th September 2012, 01:43 AM   #12
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HI.

I had a similar problem, except my amplifiers did not go "poof". I had lots of HUM.
I finally wired in a huge (2kVA) isolation transformer, that solved the problem. Since then I have remodeled the house and ripped all the old wiring out. The wiring was done by a very good crew that followed all the most current regulations. Since the rewiring I have not had any HUM problems at all.

Moral is that old wiring might not have followed the code and might have mixed up and miswired neutral and ground connections. Depending on the load in your house or the neighbors houses you may have had volts of AC between the various grounds. A central isolation transformer is the general solution, rewiring the house is the more expensive solution.

Hans J Weedon.
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Old 27th September 2012, 12:44 PM   #13
marce is online now marce  United Kingdom
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I had one socket in a house wired wrong, neutral and live swapped, it was on a small spur, but whenever we plugged anything in the RCD would trip, got an electriction in and he found the fault.
I'd get it checked.
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Old 27th September 2012, 01:36 PM   #14
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here we have those sockets that can be pugged either way, there's no such thing as "wire A must go to hot, wire B must go to neutral".
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Old 27th September 2012, 10:07 PM   #15
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Hi Push-Pull.

May I then suggest that you one of your pieces of Audio-Video is wired wrong, or has a short inside from line to chassis-ground. A second suggestion is that very old AC units had no line-transformer but used direct off the line AC to power the unit. At least in the US very cheap equipment made as late as 1955 had that, causing no end of interconnect problems.

This was especially so with really cheap radios and TVs. Those were illegal in most of Europe since 1935 or later. NEMCO, SEMCO and DEMCO ratings made sure of that. Those agencies were among the first to outlaw direct connections to the line insisting on an isolation transformer.

Hans J Weedon.
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Old 28th September 2012, 02:14 AM   #16
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My money's on transformer primary/secondary insulation breakdown.

What's bugging me is how can there be no difference between the two power leads, and how an earthed system has just two pins. The story has lots of seemingly contradictory detail. A language thing perhaps.

Two-pin mains plugs here in the UK are reversible. Three pin, earthed plugs are not. This is handy because adding the earth forces an electrical distinction between live and neutral.

For insulation test purposes, it shouldn't matter, but whether the fault manifests itself, and how and when, depends not only on the presence of an earth connection, but also on which way round the power lines are, surely?
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Old 28th September 2012, 09:41 AM   #17
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Quote:
Originally Posted by PlasticIsGood
This is handy because adding the earth forces an electrical distinction between live and neutral.
The distinction is already present, as UK mains supplies are not floating: the neutral is earthed at the substation or local transformer, and things in your house will be approximately earthed even without an earth connection. Hence the voltage between neutral and your house (and you) is, except under fault condition, much smaller than between live and your house.

The OP's problem does sound like insulation breakdown somewhere.
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Old 28th September 2012, 10:48 AM   #18
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Quote:
Originally Posted by HJWeedon View Post
Hi Push-Pull.

May I then suggest that you one of your pieces of Audio-Video is wired wrong, or has a short inside from line to chassis-ground. A second suggestion is that very old AC units had no line-transformer but used direct off the line AC to power the unit. At least in the US very cheap equipment made as late as 1955 had that, causing no end of interconnect problems.

This was especially so with really cheap radios and TVs. Those were illegal in most of Europe since 1935 or later. NEMCO, SEMCO and DEMCO ratings made sure of that. Those agencies were among the first to outlaw direct connections to the line insisting on an isolation transformer.

Hans J Weedon.
I know what you're talking about, I once took apart an old TV. the "power supply" if I may call it that was basically a diode connected directly to mains, high voltage electrolytic caps and some very large resistors used to drop voltage. and now the phones tell you to unplug the 5W SMPS when the battery is full in order to save energy

but it's not the case, there's no such thing in my system, the TV set is a SONY LCD screen.


Quote:
Originally Posted by PlasticIsGood View Post
My money's on transformer primary/secondary insulation breakdown.

What's bugging me is how can there be no difference between the two power leads, and how an earthed system has just two pins. The story has lots of seemingly contradictory detail. A language thing perhaps.
I never wrote that an earthed system has two pins. the earth came into picture either when connecting the system to an earthed outlet or when connecting the system to the TV set (the ground of the TV cable is earthed).

I reread my posts and I can't find any contradictory details, sorry.

I'm too almost sure it's breakdown of some component, either one of the low power transformers powering the additional circuitry inside the amp or the amp's SMPS. I'll do some more tests today and report back.
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Old 28th September 2012, 05:17 PM   #19
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ok. few updates.

measured from amp's SMPS ground to earth -> 0.170 mA
measured from both transformers' outpout (inside the amp) to earth -> no measurable current

so this is turning even more complicated.
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Old 19th February 2013, 12:57 AM   #20
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happened again.
secondary laptop was temporary unavailable so I had to use the laptop which is part of the "offending" system to watch a movie.
out of caution I disconnected the amp (supposed to be the faulty component) from the rest of the system. laptop only had external hard drive connected to it, absolutely nothing else. the amp remained powered though by means of the same cord extender.
I connected the TV to the laptop with a VGA cable and...
amplifier goes again. laptop fine, TV fine, external HDD fine. amp dead.
I repeat, amp was only powered from the same outlet but wasn't connected to the laptop. normally the electrical connection is by means of the DAC (laptop->DAC->amp). now the laptop->DAC amp connection wasn't there (USB cable unplugged from laptop and no other electrical connection present).
took amp apart, the digital part that controls the front-end went, as usual. AND the transformer providing power to it was VERY hot. I initially thought it was because of the 7805 regulator that shorted. but no, that wasn't the case. the heating is obviously related to the mishap but not a consequence of it.
I must confess I feel like an illiterate person trying to read Shakespeare. I'd have never imagined that such a thing can go unsolved for such a long while.
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