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Component cable voltage problem

Discussion in 'TAG McLaren Audio Owners' Forum' started by johnson, Jun 6, 2004.

  1. johnson

    johnson
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    Hi
    The reason I'm posting my problem here is because there seems to be a large amount of capable people frequenting the TMA forum and because all of my equipment is TMA(other than the plasma)

    I had removed my DVD32r from it's rack to do a little dusting.
    When i replaced it on the rack,I was gently leaning on the top of the DVD32r while trying to connect the component cable.
    I received what felt like a slight burning sensation in my arm leaning on the dvd.It turned out to be from one of the top plate screws.
    I must point out that the DVD wasn't plugged in at this stage,so I knew nothing was starting from that.
    When I dropped the component connectors the burning disappeared.
    When I picked them back up,it returned.
    I fetched my FLUKE and measured from the connector to the top plate screw.
    I am receiving about 40 volts with a slight oscillation.
    The other end of the component cable is connected to a Pioneer 433 mxe.

    Any Ideas
    Regards
    Simon
     
  2. johnson

    johnson
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    If anyone can help,I have a little more info.
    I've been looking at this all day disconnecting virtually everything.
    It seems it's not the plasma but the tag gear!!
    If I put my multi meter to my case work and to an earth I'm getting 40 volts.
    Previously when I said the dvd wasn't powered up,I forgot it was still connected to other TMA gear via Tag tronic bus and digital sinc link connections.
    With these removed and measuring across the component connections and the dvd casework the voltage disappears.
    Connect anything back up and the voltage reappears.
    Any ideas,
    Incedently with all my gear connected I get the 40 volts when I connect any piece of TMA to earth.
    Regards
     
  3. GrahamMG

    GrahamMG
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    Hi Simon.

    I was going to say that it probably a Switch mode PSU in the plasma and as the TAG gear isn't earthed you were mearly ther next best thing as this happens all the time on Sony/Denon kit etc.....Apparenly they leak the volts to the case via a few simple components so that the current never gets "interesting".

    I have also found the hairs on my arms go skywards when plugging stuff up to the TAG gear as they are "fully floating" designs as far as I can recall..

    I'd only be concerned if the current was anything above "bugger all" as that would be a fault, of course you shouldn't be plugging anything up whilst it is powered anyway........(and I mean anything)
     
  4. GrahamMG

    GrahamMG
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    Actually, I don't suppose you have an aerial lead plugged in to any of the kit? If the RF has a distribution amp nailed to it anywhere you could get a few volts sitting on the casework waiting for a hairy arm. None of this should hurt though, if it does get it checked out, a tingle and a few hairs standing up is the worst that you should feel.....
    Don't suppose you have mentioned this to the helpline guys as they could check that it is normal or not offically.....Until then it might be wise not to go poking around!!
     
  5. johnson

    johnson
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    Hi Graham
    Thanks for the reply.
    The plasma was switched off at the time and the dvd had no ac connected.
    Later I even unpluged the plasma completely and was still getting the voltage.
    One of the reasons I started thinking it was coming from th tag to the plasma and not the other way.
    I dont have any aerial leads either.(unless you count sky plus coax).
    I will check with Barry or Mark tommorow.
    Once the componrnt leads are connected to the dvd the casework has no volts,almoct as if it's using the plasma earth.
    I just was wondering what's happening to the stray voltage if the component leads are not connected.
    The case has this voltage without ac connected but as long as it's connected via tagtronic or digital link to the other components.If I remove everything else it disappears,so it could be coming from another piece of TMA gear.
    Thanks again Graham.
    Regards
    Simon
     
  6. GrahamMG

    GrahamMG
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    Have you pulled out all the leads and put them back one at a time to see which bit of kit or connection actually causes this? Then you can ask the helpdesk if it is normal?
     
  7. johnson

    johnson
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    Hi Graham
    Yes.Any thing from or to the av32r (ie sinc link or raw digital connection)
    And tagtronic bus cable from 250*3r
    And tagtronic bus cable out to 100*5r.
    Any of these connected,without actual ac connected to the dvd,results in the voltage appearing.
    Do you have a measurable voltage to earth from your casing.
    With the component cables connected there's no voltage.Maybe it's going to earth via the plasma.
    Without the component cables connected,I get 38 volts to ground from any of tha chassis of the TMA equipment.
    Regards
    Simon
     
  8. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, what you experience is entirely normal for a Class II product with a metal enclosure/case. Let me explain in more detail: All TAG McLaren Audio products are Class II, i.e. there enclosure is electrically floating. This has the advantage of typically a lower audio noise floor but comes at higher component cost, as Class II approved parts must be used. A Class I products, in contrast, connects the safety earth main wire (the yellow/green one in Europe) to the case/enclosure. This can, however, mean that there is a electrical potential difference which then can lead to hum. Quite a few American amplifiers which I have used in the past generated significant mains hum when the safety earth was connected. Unfortunately one cannot just remove the safety earth in such an instance, as this would mean that lethal voltages can reach the case.
    Class II products are therefore in terms of audio performance the better choice. Class II products can be recognised on their safety symbol, a little square in a larger one or the fact that they only have two pins at their AC connector. Just disconnect the DVD32R’s mains cable and you will see that there are just two contact.

    There are different reasons why the case can be charged, take these examples: The mains transformer, even a toroidal one, has some electro magnetic stray field. This field is reaching the metal case of your DVD32R. The enclosure acts now like a Faraday cage, i.e. it tries to compensate the static electrical field. For taht purpose electrical charge moves, statically charging the case. If you now touch the case, usually at the screws for best contact (and because there might be a higher field), you discharge the cage - that is when you feel the electrical shock. There is very little energy transmitted, hence it isn't dangerous.

    In addition, the ground of the RCA connectors connect in many products to the enclosure, hence there might be alternative reasons for the charging of the enclosure - all important, the case of a Class II product isn't discharged by any connection to the safety earth, as there is none. Sometimes there are might also be a high impedance resistor connected between case and electrical ground for electro magnetic compatibility reasons. It can lead to discharging or charging, depending on the actual condition.

    Hope this helps...
     
  9. johnson

    johnson
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    Hi Dr Zucker
    Great help thanks.
    I have recently (1 Hour ago) had a chat with Barry (helpdesk) and he said it was normal too.
    I appreciate the time taken for you to reply.
    Many thanks
    Simon
     
  10. GrahamMG

    GrahamMG
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    Hi Simon.
    There you go, as I said "fully floating", however I assumed from your previous posts that the voltage was continuous and not just a brief discharge? I'd be curious as to the current being passed when you earth it....... ;)

    Regarding Class II equipment, I'm old enough and ugly enough to cast a little pebble in this pond, whilst Udo is indeed correct in what he says and the TAG gear is perfectly within the current legisation (I can't remember but are the amps Class 1??), the original description of the square within a square symbol on Class II kit was "double insulated" and it is this that often falls foul of more intensive testing, as by definition it means two forms of insulation between you and the copper wire carrying the mains voltage. The crack here is that "air" is now allowed as the second means of insulation........I know we at the Beeb don't like this on occasion as we older types remember when a live wire that falls off an internal connection couldn't make any casework live due to the fact it was made, almost always, out of plastic (i.e. double insulated!!!!) or the wire could not ever get to any conducting material on the unit. We have and occasionally still do bond exposed metalwork to a good earth point where there is a good chance that the live wires within a unit may get to the metal case.......Some will say "over the top", some may say "it causes hum occasionally" others will say "blimey that was close"........I personally have witnessed first hand all 3 on more occasions than I care to remember.
    Whilst I naturally don't aim these comments at Udo or TAG (we examined the TAG gear just like every other bit of kit we use under our "vetters code" and with minor internal reservations it obviously passed), I would say that in general the safety type symbols on kit "on occasion" should be taken with a bit of salt, it may stop ground loops and hum but safer maybe not......The CE mark is particularly laughable.......
     
  11. johnson

    johnson
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    Hi Graham
    Thanks for the reply.
    Yes the voltage is constant.approx 38 volts,1.7 amps.
    Theis is the flow from the case to the component connectors.Then down to the plasma earth I guess!!
    Regards
    Simon
     
  12. GrahamMG

    GrahamMG
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    Hi Simon.
    If that is true, and I have no reason to doubt you, then I'd say you do have a fault somewhere, as that constant voltage and current is way above what Udo was talking about IMHO, unless they are using the case as a 0 volt rail which is very very unlikely......
    I'll check our DVD32R tonight....
     
  13. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, assuming the measurement is correct (the exchanged power seems very high), then there must be a significant ground problem somewhere. Maybe somewhere the ground connection is broken.

    P.S.: What you felt when touching the screws isn't the 38V in my opinion. Therefore, there are two independent issues.
     
  14. johnson

    johnson
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    Hi Udo,Graham,
    Thanks for the replies.
    Just to confirm.
    If the component connections are connected to the dvd32r and the plasma,I have no voltage.(it seems the plasma earth is taking care of that)

    If the component connections are diconnected,but every other connection is made,I get the 38 volts travelling between the case and the component connections (or my arm) when the multi meter is connected.

    Incedently,when the component connections arn't attached,and I connect one input of the multi meter to ANY of the cases of my tag gear(dvd32r 250*3r,100*5r and av32r case screws) and the other input to the wall socket earth,I get the 38 volts.!!
    But it must be one of the case screws,the paint doesn't conduct.

    Do You think I should contact Barry again?

    Regards
    Simon
     
  15. johnson

    johnson
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    Hi
    One more note,If you could check you dvd Graham,It would be much appreciated.
    Many thanks
    Simon
     
  16. johnson

    johnson
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    Hi
    I've just checked the voltage again.
    This time it's 22 volts and .9 amps!!
    I've no idea why it's different.Sam measuring between the case screw and the unconnected component connectors.
    I used a Fluke scopemeter to check the Fluke multi-meter and they both read the same.
    Is this more what you would expect?
    I would be very interested in what anyone else measures.
    Regards
    Simon
     
  17. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, I admit that I am a little confused about the measurment. In order to measure the potential of the DVD32R's case, you need to measure between the case and Ground.

    The RCA connectors make contact with the case, hence measuring between the case and the Component signal will show a voltage.

    Could you kindly elaborate on your measurement. Thanks
     
  18. johnson

    johnson
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    Hi Dr Zucker
    My component connections are BNC.
    When I originaly "felt" the voltage,was when I held the BNC's before connecting them.Therefore I think I was getting voltage travelling from the case screw,through my arm to the component connections to the plasma earth.(the plasma was switched off)
    Also if the BNC's are not connected,I can get the voltage from the case screw to the wall plug earth.
    The reason I'd assumed it was using the BNC's to go to the plasma earth was,I had the voltage using the hot or the ground on the BNC.
    All of this happens whether the dvd32r is on or in standby.
    With the BNC's connected and the dvd on or in standby,I get no voltage to earth.
    I hope this is clearer,If not please ask again.
    Many thanks.
    Regards
    Simon
     
  19. Dr Udo Zucker

    Dr Udo Zucker
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    THanks SImon, I am almost clear. Just clarify this part for me a little more, I didn;t understand it - or got confused:

    "All of this happens whether the dvd32r is on or in standby. With the BNC's connected and the dvd on or in standby,I get no voltage to earth."

    Thanks
     
  20. johnson

    johnson
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    Hi Udo
    What I am trying to say is,I get a voltage reading from the case screws to earth or case screws to Bnc cable(to plasma earth?) whether the unit is switched on or in standby.As long as the bnc'c are not actually connected to the unit.

    In fact I get the voltage reading even if the unit is unplugged!! but as long as it is connected to the other tag components.(via tag link,sinc link,digital cable)
    If however the unit is connected to the bnc's,I get no voltage to earth.

    Best regards
    Simon
     
  21. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, I understand now.

    Your investigation points in my opinion to a ground shift problem of one of the signals connected to one of the components - not just the DVD32R. The way to find the culprit is to disconnect one after the other input from each product within the chain. Frequently, but not always, it is found that the signal of an antenna signal amplifier, connected to a display/tv is the cause. Please let us know whaty you find.

    P.S.: the signal transmitted via a digital interconnect is pretty insensitive to ground loops, an analog signal would most likely show hum.

    P.P.S.: The signal showing the ground lift, lifts all grounds (and some of them are connected to the case of the AV32R, DVD32R...), hence you measure what you experienced.
     
  22. johnson

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    Hi Udo
    Thanks. I shall start looking.I'll let you know what I find.
    Regards
    Simon
     
  23. johnson

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    Hi Udo
    I tried a couple of things last night.(I am working 12 hour days at the moment,so don't get alot of time.)

    I started with the dvd switched off with the main power button.


    I then unplugged everything other than the power lead.

    I found that by plugging in anything to the player(Digital interconnect,sync link,tagbus from 250*3r or tag bus to 100*5r) individually or all together.I was reading 24 volts.( between the case screws and the disconnected component leads)

    If all of these are disconnected the reading is 0 volts.

    At his point I thought I'd start investigating the av or amps.

    However,with everything still disconnected from the dvd,I pushed the power button and powered up the player.

    I then read 24 volts.

    So it would seem the player provides it's own 24 volts to ground with nothing connected,as well as something else in the chain providing very similar voltage when the dvd is not powered on.

    I'm not sure what to do.
    Any help appreciated.

    Regards
    Simon
     
  24. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, two things need clarifying (at least for me):

    "I found that by plugging in anything to the player(Digital interconnect,sync link,tagbus from 250*3r or tag bus to 100*5r) individually or all together.I was reading 24 volts."

    Am I correct to assume that these connections are made on both ends or are they floating? In other wordsm when saying, e.g. connecting the Digital Interconnect, you connect it at the DVD32R AND the AV32R?

    " between the case screws and the disconnected component leads)"

    Are you measuring against the ground or the live connection of the component lead?

    Thanks for clarifying.

    If all of these are disconnected the reading is 0 volts.

    At his point I thought I'd start investigating the av or amps.

    However,with everything still disconnected from the dvd,I pushed the power button and powered up the player.

    I then read 24 volts.

    So it would seem the player provides it's own 24 volts to ground with nothing connected,as well as something else in the chain providing very similar voltage when the dvd is not powered on.

    I'm not sure what to do.
    Any help appreciated.

    Regards
    Simon[/QUOTE]
     
  25. johnson

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    Hi Udo
    In answer to your first queastion,Yes,the connections are made at both ends. So the power must be coming from the components these connections are going to ,coming from.

    With regard to your second question,the voltage is present regardless of the connection to the ground or live of the component connector.Same voltage thats why I thought this cable was being the earth.

    I hope you can help.

    Many thanks
    Simon
     
  26. johnson

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    Hi Udo
    I think I may have found the problem.
    I unplugged everything from the dvd32r.(including power lead)
    With just the tag bus cable from the 250*3r plugged to the bus input,I'm reading 87volts!!! (between the dvd case screw and the component connections)
    This is with the 250 swithced off but power lead plugged in.
    If the 250 is unplugged there is no voltage.
    If the 250 is plugged in and switched on the voltage is approx 47volts!!
    If anything else is plugged into the 250 or dvd the voltage drops lower.
    Maybe the other equipment is earthing to some degree?
    If I try this experiment with any of the other TMA equipment the voltage is zero.
    what I mean by this is ,if the av has it's tag bus outlet to the inlet of the dvd,the the voltage is zero.
    If the 100*5 has it's output to the dvd the voltage is zero.

    Am I assuming correctly?

    Regards
    Simon
     
  27. Dr Udo Zucker

    Dr Udo Zucker
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    Hi Simon, I think this confirms my initial thoughts which I like to repeat for ease of reading:

    In class II equipment the equipment ground is not connected to mains earth. Capacitive coupling between the transformer primary windings and the equipment ground results, when a system has no connection to a class I product, in the ground floating to a voltage that can be anywhere up to half the mains voltage, depending on the values of the various capacitances. The current that can be delivered is extremely small, as it is limited by the series impedances of the very small coupling capacitances. The larger the transformer, the greater the coupling and inter-winding capacitances, so power amplifiers are usually the worst culprits. This affects all class II equipment. It is basically harmless and not a safety risk.

    John Mulcahy [thanks John :clap: ], who I also discussed your findings with, pointed out that the whole topic is discussed in detail in a paper, which can be found on the Jensen Transformers site: http://www.jensentransformers.com/an/an004.pdf

    I hope this helps...
     
  28. johnson

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    Wow Thanks Udo.
    Is this still the case with the standby transformer?
    The 250 was only supplying approx 47 volts when switched on.
    The 87volts was with the power lead connected but with the main front switch off.
    Does this also mean,anyone with my combination(dvd32r av32r 100*5r 250*3r) will be experiencing similar results if they were to measure?
    Does the 100*5r use a different type of standby transformer? as this amp gave no voltage.(less than 5 volts anyway)

    Udo many thanks again.I really appreciate the time you've taken to help me out.Just like in the old forum.

    Best regards
    Simon
     
  29. johnson

    johnson
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    Hi
    Actually A slight mistake in my last post.
    I stated tah with the 250 plugged in but switched off I was reading 87 volts at the dvd.
    This is true.
    However when I stated the 100*5 was givin no voltage,I made a slight mistake.
    With the 100*5 plugged in but with the front panel switch off(as with the 250),I get 2 volts.
    But If I switch on the 100*5r I get 31 volts.So it is doing a similar thing.
    It just seems the 100*5 is actually off when the front switch is off ,and the 250 still has power when the front switch is off.
    Regards
    Simon
     
  30. Dr Udo Zucker

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    Hi Simon, all transformers will capacitively couple, it's just as said before: usually larger transformers will be worse culprits. In addition the effect will also somewhat depend on the polarity of the AC voltage, but as the actual value of the voltage is of little interest (as there is very little energy) it's not really worth doing.
     

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