polarity of power cord - gateway fpd1520

Discussion in 'Gateway' started by zirath, Mar 28, 2008.

  1. zirath

    zirath Guest

    We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
    ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
    doesn't give the polarity. A person from gateway said he thought it
    wouldn't hurt the monitor if it got plugged in backwards but I'd rather
    not try it.

    Would appreciate any help.
     
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  2. Arfa Daily

    Arfa Daily Guest

    "zirath" <> wrote in message
    news:0f2Hj.7616$Yy2.1091@trndny04...
    > We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from ebay.
    > It didn't have a power cord. It says it's a 12v dc 2.5a but it doesn't
    > give the polarity. A person from gateway said he thought it wouldn't hurt
    > the monitor if it got plugged in backwards but I'd rather not try it.
    >
    > Would appreciate any help.


    If it has got any external metal parts such as RCA (phono) connector outers,
    BNC connector outers, 'D' connector surround etc, or possibly screws for a
    stand, as these often go right through the plastic case, and into the
    internal chassis, then try measuring from any such metal to each of the DC
    power input connector's terminals in turn, using an ohm meter. Chances are
    you'll find a direct connection, and that will be your DC ground ( "-" )
    connection. The other will then be the "+". Assuming that it's a 'standard'
    co-axial DC connector, on most modern equipment, 'pin' is "+" and side
    contact is "-" although that's not cast in stone. Be aware when you are
    obtaining a replacement PSU, that the plug is often a slightly abnormal
    size, being a little larger than those you typically find on 'general' power
    supplies. Also, make sure that you get one well rated for the job, as these
    monitors do draw quite a lot of current, and may well surge up close to the
    quoted 2.5 amps at startup, as the LCD backlights first fire up before
    settling to their run current.

    As to whether it would be safe to reverse connect it, I wouldn't like to
    say. Some equipment is perfectly well protected against such 'consumer
    antics', but it is by no means guaranteed, and if it is not adequately
    protected, the result is often an item that's fried beyond repair, for no
    other reason than unobtainable power supply devices, as many previous posts
    on this subject over the years, will attest ...

    Arfa
     
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  3. Arfa Daily

    Arfa Daily Guest

    "William Sommerwerck" <> wrote in message
    news:...
    > "Arfa Daily" <> wrote in message
    > news:Wb3Hj.18668$...
    >
    >> If it has got any external metal parts such as RCA (phono) connector
    >> outers, BNC connector outers, 'D' connector surround etc, or possibly
    >> screws for a stand, as these often go right through the plastic case,
    >> and into the internal chassis, then try measuring from any such metal to
    >> each of the DC power input connector's terminals in turn, using an ohm
    >> meter. Chances are you'll find a direct connection, and that will be your
    >> DC ground ( "-" ) connection. The other will then be the "+".

    >
    > Arfa, you're usually dead-on, but this is quite incorrect. The side of the
    > connector that's "grounded" is not necessarily negative! A transistor
    > radio
    > using PNP transistors would (presumably) have a positive ground, not
    > negative.



    I think you'll find that on 'most' modern - and I did say "modern" in my
    original reply - equipment, this has been pretty much standardised such that
    DC "-" *is* common ground. Sony kit that I have seen in recent years has all
    obeyed this 'convention', so I'm willing to bet that any Sony items that
    follow the opposite 'convention', are not "modern". Pin = "-" used to be the
    'convention', but for all mainstream manufacturers whose equipment I work
    on, this has not been the case for many years. It was only usually the
    Japanese manufacturers that followed this anyway, as I recall.

    As for a transistor radio that uses PNP transistors, I haven't seen one that
    uses transistors at all for many years, let alone PNP ones, so I think you
    might be struggling to fit that into my "modern" category, also.


    >
    >
    >> Assuming that it's a 'standard' co-axial DC connector, on most modern
    >> equipment, 'pin' is "+" and side contact is "-" although that's not cast

    > in
    >> stone.

    >
    > No, it's not. I have Sony equipment where the pin is negative, not
    > positive.
    >
    >
    > Rather than seeing which side of the power connector is grounded, I would
    > look to see which side of the electrolytic capacitors is grounded.
    >


    This is, of course, the very best way, if the owner wants the trouble of
    taking it all to bits, and identifying a suitable electrolytic to use as his
    reference. However, I would put my name on the line that the method I quoted
    before, would 99.5% yield the same result, with any 'modern' item using a
    coaxial DC socket. Perhaps someone out there with a Gateway monitor could
    confirm which way round it is, then neither of us will be applying guesswork
    to experience and coming up with sage advice ... d;~}

    Arfa
     
  4. BillW50

    BillW50 Guest

    In news:KS5Hj.22783$,
    Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    [...]
    > As for a transistor radio that uses PNP transistors, I haven't seen
    > one that uses transistors at all for many years, let alone PNP ones,
    > so I think you might be struggling to fit that into my "modern"
    > category, also.


    Well Arfa... they still use transistors (both NPN and PNP types) in
    modern equipment. The reason you don't see them anymore is do to the
    magic of minturization. But they are still there, just neatly packaged
    into what is known today as the intergrated circuit (IC chip). :D

    --
    Bill
     
  5. Arfa Daily

    Arfa Daily Guest

    "BillW50" <> wrote in message
    news:47ecf425$0$1345$...
    > In news:KS5Hj.22783$,
    > Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    > [...]
    >> As for a transistor radio that uses PNP transistors, I haven't seen
    >> one that uses transistors at all for many years, let alone PNP ones,
    >> so I think you might be struggling to fit that into my "modern"
    >> category, also.

    >
    > Well Arfa... they still use transistors (both NPN and PNP types) in modern
    > equipment. The reason you don't see them anymore is do to the magic of
    > minturization. But they are still there, just neatly packaged into what is
    > known today as the intergrated circuit (IC chip). :D
    >
    > --
    > Bill

    And I though I was pedantic !! Yes, of course ICs contain transistors, and
    yes, I would accept that some of them may be PNP types, depending on block
    function within the IC, but I don't think, with the best will in the world,
    that this is the level of transistor existence that William was referring to
    with his "transistor radio using PNP transistors" scenario. In any event, in
    the case of an IC taking a single polarity rail, it is irrelevant whether
    the transistors inside are NPN or PNP or FETs or whatever. PNP transistors
    are just used 'upside down', as are discrete PNP transistors when used in
    any piece of single polarity rail equipment. The ground is still (typically
    for //modern// equipment) the "-" side of the power supply / battery.

    Anyway, this is getting out of hand. The OP aked a simple question, and I
    gave a simple answer. This afternoon, I was in a friend's computer repair
    shop. Bear in mind that he deals with monitors of all types and makes on a
    daily basis. I asked him how he would go about determining the polarity of
    such a monitor, and he said that he would stick one side of his ohm meter on
    one of the D connector locking screws, and the other on each pin of the DC
    connector. When he found the pin that read short to the connector locking
    screw, it was his contention that he would have identified the "-" side of
    the power supply. So that's pretty much exactly what I said. He also frowned
    and shook his head, and said that he couldn't remember how many years it had
    been since he had seen a DC connector that had the pin as the "-".

    Which is also pretty much what I said ...

    Arfa
     
  6. Guest

    On 3ÔÂ28ÈÕ, ÏÂÎç4ʱ45·Ö, zirath <> wrote:
    > We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
    > ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
    > doesn't give the polarity. A person from gateway said he thought it
    > wouldn't hurt the monitor if it got plugged in backwards but I'd rather
    > not try it.
    >
    > Would appreciate any help.




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  7. Arfa Daily

    Arfa Daily Guest

    "James Sweet" <> wrote in message
    news:kjhHj.461$oE1.370@trndny09...
    >
    >
    > "William Sommerwerck" <> wrote in message
    > news:...
    >>> On the monitor it should be marked or say something
    >>> in the manual.

    >>
    >> "The Lady from Philadelphia" forgot the obvious. Power sockets almost
    >> always
    >> have their polarity marked.
    >>
    >>

    >
    > I've certainly seen plenty of them that didn't though.
    >

    Likewise

    Arfa
     
  8. James Sweet

    James Sweet Guest

    "William Sommerwerck" <> wrote in message
    news:...
    >> On the monitor it should be marked or say something
    >> in the manual.

    >
    > "The Lady from Philadelphia" forgot the obvious. Power sockets almost
    > always
    > have their polarity marked.
    >
    >


    I've certainly seen plenty of them that didn't though.
     
  9. Guest

    On 3ÔÂ28ÈÕ, ÏÂÎç4ʱ45·Ö, zirath <> wrote:
    > We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
    > ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
    > doesn't give the polarity. A person from gateway said he thought it
    > wouldn't hurt the monitor if it got plugged in backwards but I'd rather
    > not try it.
    >
    > Would appreciate any help.




    Do you want access to China's massive pool of electronic
    manufacturers... but lack the time to contact suppliers, negotiate
    contracts, arrange shipping or monitor product quality? Don't worry -
    Let seriouswholesale deal with all that for you.

    *Check out the huge range of Gadgets, MP3 / MP4 Players, Car DVD /
    Audio, and Computer Accessories now by visiting the online wholesale
    catalog at seriouswholesale. com You'll have peace of mind thanks to
    the seriouswholesale Quality Control, 12-month Warranty on all
    products, and easy secure payment by credit card through Paypal.

    Selling on eBay or your own online store? Send products direct from
    our warehouse to your customers using our unique drop-shipping
    service. You can profit by selling hundreds of different products,
    without holding any of your own inventory! Any questions you have will
    be answered by the seriouswholesale English-speaking customer support
    team... Their aim is to make your China electronics importing business
    easier to run than ever before.

    Welcome to http://www.seriouswholesale.com.

    seriouswholesale - Buy from the source, profit without the hassle.

    - 12 Months Warranty - No minimum order restrictions - Drop-shipping
    with no additional fee - Pay by safely by PayPal seriouswholesale
    Wholesale Co., Ltd.: Chinas original and best online electronics
    wholesaler & drop-shipper: seriouswholesale. com
     
  10. zirath

    zirath Guest

    zirath wrote:
    > We recently got a gateway fpd1520 (15" lcd flatscreen) monitor from
    > ebay. It didn't have a power cord. It says it's a 12v dc 2.5a but it
    > doesn't give the polarity. A person from gateway said he thought it
    > wouldn't hurt the monitor if it got plugged in backwards but I'd rather
    > not try it.
    >
    > Would appreciate any help.


    Thanks to everyone for your help.
     
  11. BillW50

    BillW50 Guest

    In news:xJ8Hj.20508$,
    Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
    > "BillW50" <> wrote in message
    > news:47ecf425$0$1345$...
    >> In news:KS5Hj.22783$,
    >> Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    >> [...]
    >>> As for a transistor radio that uses PNP transistors, I haven't seen
    >>> one that uses transistors at all for many years, let alone PNP ones,
    >>> so I think you might be struggling to fit that into my "modern"
    >>> category, also.

    >>
    >> Well Arfa... they still use transistors (both NPN and PNP types) in
    >> modern equipment. The reason you don't see them anymore is do to the
    >> magic of minturization. But they are still there, just neatly
    >> packaged into what is known today as the intergrated circuit (IC
    >> chip). :D

    >
    > And I though I was pedantic !! Yes, of course ICs contain
    > transistors, and yes, I would accept that some of them may be PNP
    > types, depending on block function within the IC, but I don't think,
    > with the best will in the world, that this is the level of transistor
    > existence that William was referring to with his "transistor radio
    > using PNP transistors" scenario. In any event, in the case of an IC
    > taking a single polarity rail, it is irrelevant whether the
    > transistors inside are NPN or PNP or FETs or whatever. PNP
    > transistors are just used 'upside down', as are discrete PNP
    > transistors when used in any piece of single polarity rail equipment.
    > The ground is still (typically for //modern// equipment) the "-" side
    > of the power supply / battery.
    > Anyway, this is getting out of hand. The OP aked a simple question,
    > and I gave a simple answer. This afternoon, I was in a friend's
    > computer repair shop. Bear in mind that he deals with monitors of all
    > types and makes on a daily basis. I asked him how he would go about
    > determining the polarity of such a monitor, and he said that he would
    > stick one side of his ohm meter on one of the D connector locking
    > screws, and the other on each pin of the DC connector. When he found
    > the pin that read short to the connector locking screw, it was his
    > contention that he would have identified the "-" side of the power
    > supply. So that's pretty much exactly what I said. He also frowned
    > and shook his head, and said that he couldn't remember how many years
    > it had been since he had seen a DC connector that had the pin as the
    > "-".
    > Which is also pretty much what I said ...
    >
    > Arfa


    That would be okay if it were a negative ground system. But like what
    William Sommerwerck mentioned, we don't know that. The way I would do it
    is to ohm the the power in. And the lower resistance would be the
    correct polarity. Although you would need another meter to read the
    polarity of the ohm meter. As they are not standardized on multimeters.
    You could also use a diode (or LED) to learn of the polarity of the
    meter as well.

    --
    Bill
     
  12. Arfa Daily

    Arfa Daily Guest

    "BillW50" <> wrote in message
    news:47ef748f$0$1347$...
    > In news:xJ8Hj.20508$,
    > Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
    >> "BillW50" <> wrote in message
    >> news:47ecf425$0$1345$...
    >>> In news:KS5Hj.22783$,
    >>> Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    >>> [...]
    >>>> As for a transistor radio that uses PNP transistors, I haven't seen
    >>>> one that uses transistors at all for many years, let alone PNP ones,
    >>>> so I think you might be struggling to fit that into my "modern"
    >>>> category, also.
    >>>
    >>> Well Arfa... they still use transistors (both NPN and PNP types) in
    >>> modern equipment. The reason you don't see them anymore is do to the
    >>> magic of minturization. But they are still there, just neatly
    >>> packaged into what is known today as the intergrated circuit (IC
    >>> chip). :D

    >>
    >> And I though I was pedantic !! Yes, of course ICs contain
    >> transistors, and yes, I would accept that some of them may be PNP
    >> types, depending on block function within the IC, but I don't think,
    >> with the best will in the world, that this is the level of transistor
    >> existence that William was referring to with his "transistor radio
    >> using PNP transistors" scenario. In any event, in the case of an IC
    >> taking a single polarity rail, it is irrelevant whether the
    >> transistors inside are NPN or PNP or FETs or whatever. PNP
    >> transistors are just used 'upside down', as are discrete PNP
    >> transistors when used in any piece of single polarity rail equipment.
    >> The ground is still (typically for //modern// equipment) the "-" side
    >> of the power supply / battery.
    >> Anyway, this is getting out of hand. The OP aked a simple question,
    >> and I gave a simple answer. This afternoon, I was in a friend's
    >> computer repair shop. Bear in mind that he deals with monitors of all
    >> types and makes on a daily basis. I asked him how he would go about
    >> determining the polarity of such a monitor, and he said that he would
    >> stick one side of his ohm meter on one of the D connector locking
    >> screws, and the other on each pin of the DC connector. When he found
    >> the pin that read short to the connector locking screw, it was his
    >> contention that he would have identified the "-" side of the power
    >> supply. So that's pretty much exactly what I said. He also frowned
    >> and shook his head, and said that he couldn't remember how many years
    >> it had been since he had seen a DC connector that had the pin as the
    >> "-".
    >> Which is also pretty much what I said ...
    >>
    >> Arfa

    >
    > That would be okay if it were a negative ground system. But like what
    > William Sommerwerck mentioned, we don't know that. The way I would do it
    > is to ohm the the power in. And the lower resistance would be the correct
    > polarity. Although you would need another meter to read the polarity of
    > the ohm meter. As they are not standardized on multimeters. You could also
    > use a diode (or LED) to learn of the polarity of the meter as well.
    >
    > --
    > Bill


    JHC !!! Do you not understand the word "modern" ? Do you not understand the
    phrase "... deals with monitors of all types on a daily basis" ? I repair
    this stuff all day every day for a living. I have done for over 35 years. I
    cannot remember the last time I saw a piece of kit of any description, which
    employed a positive ground. My friend, who owns a computer repair shop, and
    has done for many years, cannot remember the last time - if ever - that he
    saw a monitor with an external power supply, that was not negative ground
    with the connector sleeve as the negative connection.

    With so much interconnectivity between household items now, there has had to
    be a degree of standardisation on this issue, and it has evolved through a
    general concensus amongst manufacturers, that negative ground will be the
    convention.

    As for your method of determining polarity, it makes no sense at all, unless
    you are assuming a series diode, which is quite unlikely in most modern kit,
    as it represents a waste of power due to its forward voltage drop. It may
    even have a shunt protection diode, in which case, your 'test' will ensure
    that the polarity is determined INcorrectly. Even if the device did have a
    series diode, depending on where the supply first goes, there is still no
    guarantee that there will be any reading at all on a standard multimeter on
    ohms. If there is not any diode - series or shunt - any reading of ohms
    obtained across the input socket, is unlikely to reveal anything meaningful.
    What is your experience in fault-finding, I wonder, to have caused you to
    have formulated such a bizarre method, and believe that it would
    uncategorically give you a correct result ?

    Arfa
     
  13. BillW50

    BillW50 Guest

    In news:gnNHj.25773$,
    Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
    > "BillW50" <> wrote in message
    > news:47ef748f$0$1347$...
    >> In news:xJ8Hj.20508$,
    >> Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
    >>> "BillW50" <> wrote in message
    >>> news:47ecf425$0$1345$...
    >>>> In news:KS5Hj.22783$,
    >>>> Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    >>>> [...]
    >>>>> As for a transistor radio that uses PNP transistors, I haven't
    >>>>> seen one that uses transistors at all for many years, let alone
    >>>>> PNP ones, so I think you might be struggling to fit that into my
    >>>>> "modern" category, also.
    >>>>
    >>>> Well Arfa... they still use transistors (both NPN and PNP types) in
    >>>> modern equipment. The reason you don't see them anymore is do to
    >>>> the magic of minturization. But they are still there, just neatly
    >>>> packaged into what is known today as the intergrated circuit (IC
    >>>> chip). :D
    >>>
    >>> And I though I was pedantic !! Yes, of course ICs contain
    >>> transistors, and yes, I would accept that some of them may be PNP
    >>> types, depending on block function within the IC, but I don't think,
    >>> with the best will in the world, that this is the level of
    >>> transistor existence that William was referring to with his
    >>> "transistor radio using PNP transistors" scenario. In any event, in
    >>> the case of an IC taking a single polarity rail, it is irrelevant
    >>> whether the transistors inside are NPN or PNP or FETs or whatever.
    >>> PNP transistors are just used 'upside down', as are discrete PNP
    >>> transistors when used in any piece of single polarity rail
    >>> equipment. The ground is still (typically for //modern// equipment)
    >>> the "-" side of the power supply / battery.
    >>> Anyway, this is getting out of hand. The OP aked a simple question,
    >>> and I gave a simple answer. This afternoon, I was in a friend's
    >>> computer repair shop. Bear in mind that he deals with monitors of
    >>> all types and makes on a daily basis. I asked him how he would go
    >>> about determining the polarity of such a monitor, and he said that
    >>> he would stick one side of his ohm meter on one of the D connector
    >>> locking screws, and the other on each pin of the DC connector. When
    >>> he found the pin that read short to the connector locking screw, it
    >>> was his contention that he would have identified the "-" side of
    >>> the power supply. So that's pretty much exactly what I said. He
    >>> also frowned and shook his head, and said that he couldn't remember
    >>> how many years it had been since he had seen a DC connector that
    >>> had the pin as the "-".
    >>> Which is also pretty much what I said ...
    >>>
    >>> Arfa

    >>
    >> That would be okay if it were a negative ground system. But like what
    >> William Sommerwerck mentioned, we don't know that. The way I would
    >> do it is to ohm the the power in. And the lower resistance would be
    >> the correct polarity. Although you would need another meter to read
    >> the polarity of the ohm meter. As they are not standardized on
    >> multimeters. You could also use a diode (or LED) to learn of the
    >> polarity of the meter as well. --
    >> Bill

    >
    > JHC !!! Do you not understand the word "modern" ? Do you not
    > understand the phrase "... deals with monitors of all types on a
    > daily basis" ? I repair this stuff all day every day for a living. I
    > have done for over 35 years. I cannot remember the last time I saw a
    > piece of kit of any description, which employed a positive ground. My
    > friend, who owns a computer repair shop, and has done for many years,
    > cannot remember the last time - if ever - that he saw a monitor with
    > an external power supply, that was not negative ground with the
    > connector sleeve as the negative connection.
    > With so much interconnectivity between household items now, there has
    > had to be a degree of standardisation on this issue, and it has
    > evolved through a general concensus amongst manufacturers, that
    > negative ground will be the convention.
    >
    > As for your method of determining polarity, it makes no sense at all,
    > unless you are assuming a series diode, which is quite unlikely in
    > most modern kit, as it represents a waste of power due to its forward
    > voltage drop. It may even have a shunt protection diode, in which
    > case, your 'test' will ensure that the polarity is determined
    > INcorrectly. Even if the device did have a series diode, depending on
    > where the supply first goes, there is still no guarantee that there
    > will be any reading at all on a standard multimeter on ohms. If there
    > is not any diode - series or shunt - any reading of ohms obtained
    > across the input socket, is unlikely to reveal anything meaningful.
    > What is your experience in fault-finding, I wonder, to have caused
    > you to have formulated such a bizarre method, and believe that it
    > would uncategorically give you a correct result ?
    > Arfa


    Actually being an electrical engineer for 35 years, I could careless how
    long your friend has been repairing computers. And the reason why the
    ohm meter works is because all of the curcuits are in parallel with the
    supply. Thus you will get a lower reading when the polarity is correct.
    And you will get a higher reading when it is not correct. Thus as all of
    the circuits are reversed biased.

    Whether or not all manufactures use negative ground or not, I have no
    idea. Although in all of my experience, I have learned to never assume
    anything. And I have seen many strange designs. One of them had an OP
    amp's output connected directly to ground. I was confused about that one
    until I chatted with the designer. Then it all made sense. :)

    --
    Bill
     
  14. James Sweet

    James Sweet Guest


    >
    > JHC !!! Do you not understand the word "modern" ? Do you not understand
    > the phrase "... deals with monitors of all types on a daily basis" ? I
    > repair this stuff all day every day for a living. I have done for over 35
    > years. I cannot remember the last time I saw a piece of kit of any
    > description, which employed a positive ground. My friend, who owns a
    > computer repair shop, and has done for many years, cannot remember the
    > last time - if ever - that he saw a monitor with an external power supply,
    > that was not negative ground with the connector sleeve as the negative
    > connection.
    >
    > With so much interconnectivity between household items now, there has had
    > to be a degree of standardisation on this issue, and it has evolved
    > through a general concensus amongst manufacturers, that negative ground
    > will be the convention.
    >
    > As for your method of determining polarity, it makes no sense at all,
    > unless you are assuming a series diode, which is quite unlikely in most
    > modern kit, as it represents a waste of power due to its forward voltage
    > drop. It may even have a shunt protection diode, in which case, your
    > 'test' will ensure that the polarity is determined INcorrectly. Even if
    > the device did have a series diode, depending on where the supply first
    > goes, there is still no guarantee that there will be any reading at all on
    > a standard multimeter on ohms. If there is not any diode - series or
    > shunt - any reading of ohms obtained across the input socket, is unlikely
    > to reveal anything meaningful. What is your experience in fault-finding, I
    > wonder, to have caused you to have formulated such a bizarre method, and
    > believe that it would uncategorically give you a correct result ?
    >
    > Arfa
    >


    I've been working on this stuff for years as well, not as long as you, but I
    haven't been alive as long as you've been at it either. I've never seen a
    positive ground either, it would make no sense to do it that way. It's just
    standard that this stuff is negative ground, and that metal parts of the
    chassis are grounded for shielding, I've never once seen a case where this
    wasn't true so it's good enough for me. If one is still in doubt, pop the
    cover off and check the polarity of the filter lytics.
     
  15. Arfa Daily

    Arfa Daily Guest

    "BillW50" <> wrote in message
    news:47efba6b$0$1344$...
    > In news:gnNHj.25773$,
    > Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
    >> "BillW50" <> wrote in message
    >> news:47ef748f$0$1347$...
    >>> In news:xJ8Hj.20508$,
    >>> Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
    >>>> "BillW50" <> wrote in message
    >>>> news:47ecf425$0$1345$...
    >>>>> In news:KS5Hj.22783$,
    >>>>> Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    >>>>> [...]
    >>>>>> As for a transistor radio that uses PNP transistors, I haven't
    >>>>>> seen one that uses transistors at all for many years, let alone
    >>>>>> PNP ones, so I think you might be struggling to fit that into my
    >>>>>> "modern" category, also.
    >>>>>
    >>>>> Well Arfa... they still use transistors (both NPN and PNP types) in
    >>>>> modern equipment. The reason you don't see them anymore is do to
    >>>>> the magic of minturization. But they are still there, just neatly
    >>>>> packaged into what is known today as the intergrated circuit (IC
    >>>>> chip). :D
    >>>>
    >>>> And I though I was pedantic !! Yes, of course ICs contain
    >>>> transistors, and yes, I would accept that some of them may be PNP
    >>>> types, depending on block function within the IC, but I don't think,
    >>>> with the best will in the world, that this is the level of
    >>>> transistor existence that William was referring to with his
    >>>> "transistor radio using PNP transistors" scenario. In any event, in
    >>>> the case of an IC taking a single polarity rail, it is irrelevant
    >>>> whether the transistors inside are NPN or PNP or FETs or whatever.
    >>>> PNP transistors are just used 'upside down', as are discrete PNP
    >>>> transistors when used in any piece of single polarity rail
    >>>> equipment. The ground is still (typically for //modern// equipment)
    >>>> the "-" side of the power supply / battery.
    >>>> Anyway, this is getting out of hand. The OP aked a simple question,
    >>>> and I gave a simple answer. This afternoon, I was in a friend's
    >>>> computer repair shop. Bear in mind that he deals with monitors of
    >>>> all types and makes on a daily basis. I asked him how he would go
    >>>> about determining the polarity of such a monitor, and he said that
    >>>> he would stick one side of his ohm meter on one of the D connector
    >>>> locking screws, and the other on each pin of the DC connector. When
    >>>> he found the pin that read short to the connector locking screw, it
    >>>> was his contention that he would have identified the "-" side of
    >>>> the power supply. So that's pretty much exactly what I said. He
    >>>> also frowned and shook his head, and said that he couldn't remember
    >>>> how many years it had been since he had seen a DC connector that
    >>>> had the pin as the "-".
    >>>> Which is also pretty much what I said ...
    >>>>
    >>>> Arfa
    >>>
    >>> That would be okay if it were a negative ground system. But like what
    >>> William Sommerwerck mentioned, we don't know that. The way I would
    >>> do it is to ohm the the power in. And the lower resistance would be
    >>> the correct polarity. Although you would need another meter to read
    >>> the polarity of the ohm meter. As they are not standardized on
    >>> multimeters. You could also use a diode (or LED) to learn of the
    >>> polarity of the meter as well. --
    >>> Bill

    >>
    >> JHC !!! Do you not understand the word "modern" ? Do you not
    >> understand the phrase "... deals with monitors of all types on a
    >> daily basis" ? I repair this stuff all day every day for a living. I
    >> have done for over 35 years. I cannot remember the last time I saw a
    >> piece of kit of any description, which employed a positive ground. My
    >> friend, who owns a computer repair shop, and has done for many years,
    >> cannot remember the last time - if ever - that he saw a monitor with
    >> an external power supply, that was not negative ground with the
    >> connector sleeve as the negative connection.
    >> With so much interconnectivity between household items now, there has
    >> had to be a degree of standardisation on this issue, and it has
    >> evolved through a general concensus amongst manufacturers, that
    >> negative ground will be the convention.
    >>
    >> As for your method of determining polarity, it makes no sense at all,
    >> unless you are assuming a series diode, which is quite unlikely in
    >> most modern kit, as it represents a waste of power due to its forward
    >> voltage drop. It may even have a shunt protection diode, in which
    >> case, your 'test' will ensure that the polarity is determined
    >> INcorrectly. Even if the device did have a series diode, depending on
    >> where the supply first goes, there is still no guarantee that there
    >> will be any reading at all on a standard multimeter on ohms. If there
    >> is not any diode - series or shunt - any reading of ohms obtained
    >> across the input socket, is unlikely to reveal anything meaningful.
    >> What is your experience in fault-finding, I wonder, to have caused
    >> you to have formulated such a bizarre method, and believe that it
    >> would uncategorically give you a correct result ?
    >> Arfa

    >
    > Actually being an electrical engineer for 35 years, I could careless how
    > long your friend has been repairing computers. And the reason why the ohm
    > meter works is because all of the curcuits are in parallel with the
    > supply. Thus you will get a lower reading when the polarity is correct.
    > And you will get a higher reading when it is not correct. Thus as all of
    > the circuits are reversed biased.


    That is unmitigated nonsense. If there is a shunt protection diode, it will
    be FORWARD biased when the polarity is WRONG. Also, the fact that my friend
    repairs this stuff all day, and as an electrical engineer, you clearly do
    not, that makes him an expert, compared to you ...

    >
    > Whether or not all manufactures use negative ground or not, I have no
    > idea.


    Well, as I repair this stuff all day as well, I *do* have an idea, so that
    clearly also makes me more of an expert on this particular subject, than
    you ...

    >Although in all of my experience, I have learned to never assume anything.
    >And I have seen many strange designs. One of them had an OP amp's output
    >connected directly to ground. I was confused about that one until I chatted
    >with the designer. Then it all made sense. :)
    >
    > --
    > Bill


    In general, I would agree with you not to assume anything, but some things
    are a matter of convention, and in recent years, based on my direct
    experience of such things, I would stick my neck on the line, and say that
    this is one, and that all modern kit, manufactured for the domestic market,
    employs circuitry with a negative ground, to which (most) external metalwork
    is firmly bonded.

    Arfa
     
  16. BillW50

    BillW50 Guest

    In news:,
    Michael A. Terrell typed on Sun, 30 Mar 2008 11:48:38 -0400:
    >
    > I guess that no one bothered to check out the link I posted to a
    > replacement supply that not only shows it to be center positive, but
    > it tells you which coaxial power plug you need.


    Yes we know Michael. And thanks again. :)

    > aioe.org is home to cowards and terrorists
    >
    > Add this line to your news proxy nfilter.dat file
    > * drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.


    Why do you say that? aioe is based in Italy.

    --
    Bill
     
  17. BillW50

    BillW50 Guest

    In news:Z8PHj.18868$,
    Arfa Daily typed on Sun, 30 Mar 2008 16:24:25 GMT:
    > "BillW50" <> wrote in message
    > news:47efba6b$0$1344$...
    >> In news:gnNHj.25773$,
    >> Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
    >>> "BillW50" <> wrote in message
    >>> news:47ef748f$0$1347$...
    >>>> In news:xJ8Hj.20508$,
    >>>> Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
    >>>>> "BillW50" <> wrote in message
    >>>>> news:47ecf425$0$1345$...
    >>>>>> In news:KS5Hj.22783$,
    >>>>>> Arfa Daily typed on Fri, 28 Mar 2008 12:52:58 GMT:
    >>>>>> [...]
    >>>>>>> As for a transistor radio that uses PNP transistors, I haven't
    >>>>>>> seen one that uses transistors at all for many years, let alone
    >>>>>>> PNP ones, so I think you might be struggling to fit that into my
    >>>>>>> "modern" category, also.
    >>>>>>
    >>>>>> Well Arfa... they still use transistors (both NPN and PNP types)
    >>>>>> in modern equipment. The reason you don't see them anymore is do
    >>>>>> to the magic of minturization. But they are still there, just
    >>>>>> neatly packaged into what is known today as the intergrated
    >>>>>> circuit (IC chip). :D
    >>>>>
    >>>>> And I though I was pedantic !! Yes, of course ICs contain
    >>>>> transistors, and yes, I would accept that some of them may be PNP
    >>>>> types, depending on block function within the IC, but I don't
    >>>>> think, with the best will in the world, that this is the level of
    >>>>> transistor existence that William was referring to with his
    >>>>> "transistor radio using PNP transistors" scenario. In any event,
    >>>>> in the case of an IC taking a single polarity rail, it is
    >>>>> irrelevant whether the transistors inside are NPN or PNP or FETs
    >>>>> or whatever. PNP transistors are just used 'upside down', as are
    >>>>> discrete PNP transistors when used in any piece of single
    >>>>> polarity rail equipment. The ground is still (typically for
    >>>>> //modern// equipment) the "-" side of the power supply / battery.
    >>>>> Anyway, this is getting out of hand. The OP aked a simple
    >>>>> question, and I gave a simple answer. This afternoon, I was in a
    >>>>> friend's computer repair shop. Bear in mind that he deals with
    >>>>> monitors of all types and makes on a daily basis. I asked him how
    >>>>> he would go about determining the polarity of such a monitor, and
    >>>>> he said that he would stick one side of his ohm meter on one of
    >>>>> the D connector locking screws, and the other on each pin of the
    >>>>> DC connector. When he found the pin that read short to the
    >>>>> connector locking screw, it was his contention that he would have
    >>>>> identified the "-" side of the power supply. So that's pretty
    >>>>> much exactly what I said. He also frowned and shook his head, and
    >>>>> said that he couldn't remember how many years it had been since
    >>>>> he had seen a DC connector that had the pin as the "-".
    >>>>> Which is also pretty much what I said ...
    >>>>>
    >>>>> Arfa
    >>>>
    >>>> That would be okay if it were a negative ground system. But like
    >>>> what William Sommerwerck mentioned, we don't know that. The way I
    >>>> would do it is to ohm the the power in. And the lower resistance
    >>>> would be the correct polarity. Although you would need another
    >>>> meter to read the polarity of the ohm meter. As they are not
    >>>> standardized on multimeters. You could also use a diode (or LED)
    >>>> to learn of the polarity of the meter as well. --
    >>>> Bill
    >>>
    >>> JHC !!! Do you not understand the word "modern" ? Do you not
    >>> understand the phrase "... deals with monitors of all types on a
    >>> daily basis" ? I repair this stuff all day every day for a living. I
    >>> have done for over 35 years. I cannot remember the last time I saw a
    >>> piece of kit of any description, which employed a positive ground.
    >>> My friend, who owns a computer repair shop, and has done for many
    >>> years, cannot remember the last time - if ever - that he saw a
    >>> monitor with an external power supply, that was not negative ground
    >>> with the connector sleeve as the negative connection.
    >>> With so much interconnectivity between household items now, there
    >>> has had to be a degree of standardisation on this issue, and it has
    >>> evolved through a general concensus amongst manufacturers, that
    >>> negative ground will be the convention.
    >>>
    >>> As for your method of determining polarity, it makes no sense at
    >>> all, unless you are assuming a series diode, which is quite
    >>> unlikely in most modern kit, as it represents a waste of power due
    >>> to its forward voltage drop. It may even have a shunt protection
    >>> diode, in which case, your 'test' will ensure that the polarity is
    >>> determined INcorrectly. Even if the device did have a series diode,
    >>> depending on where the supply first goes, there is still no
    >>> guarantee that there will be any reading at all on a standard
    >>> multimeter on ohms. If there is not any diode - series or shunt -
    >>> any reading of ohms obtained across the input socket, is unlikely
    >>> to reveal anything meaningful. What is your experience in
    >>> fault-finding, I wonder, to have caused you to have formulated such
    >>> a bizarre method, and believe that it would uncategorically give
    >>> you a correct result ? Arfa

    >>
    >> Actually being an electrical engineer for 35 years, I could careless
    >> how long your friend has been repairing computers. And the reason
    >> why the ohm meter works is because all of the curcuits are in
    >> parallel with the supply. Thus you will get a lower reading when the
    >> polarity is correct. And you will get a higher reading when it is
    >> not correct. Thus as all of the circuits are reversed biased.

    >
    > That is unmitigated nonsense. If there is a shunt protection diode,
    > it will be FORWARD biased when the polarity is WRONG. Also, the fact
    > that my friend repairs this stuff all day, and as an electrical
    > engineer, you clearly do not, that makes him an expert, compared to
    > you ...


    If there was a shunt protection diode, then both resistance measurements
    would be forward biased. Thus you would know that since there was no
    high resistance reading. But let's assume and use your plan for a
    minute. There are plenty of examples where they don't ground the shield
    but just let it float. Yes it sounds stupid I know, but it has been done
    from time to time. And I worry about everything seemingly coming from
    China nowadays. Which IMHO is only going to make things worse. And some
    of this stuff from China, isn't even UL or FCC approved.

    >> Whether or not all manufactures use negative ground or not, I have no
    >> idea.

    >
    > Well, as I repair this stuff all day as well, I *do* have an idea, so
    > that clearly also makes me more of an expert on this particular
    > subject, than you ...


    That is indeed possible. I always said and believed that we can learn a
    lot even from a child. :)

    >> Although in all of my experience, I have learned to never assume
    >> anything. And I have seen many strange designs. One of them had an
    >> OP amp's output connected directly to ground. I was confused about
    >> that one until I chatted with the designer. Then it all made sense.
    >> :) --
    >> Bill

    >
    > In general, I would agree with you not to assume anything, but some
    > things are a matter of convention, and in recent years, based on my
    > direct experience of such things, I would stick my neck on the line,
    > and say that this is one, and that all modern kit, manufactured for
    > the domestic market, employs circuitry with a negative ground, to
    > which (most) external metalwork is firmly bonded.
    >
    > Arfa


    I also have seen grounds that wasn't really ground either. Shields that
    were not connected to anything. Lots of weird stuff goes on in consumer
    grade equipment. Most of it IMHO is done to save a buck. Some of it is
    just ingenious! And some of it is just sloppy engineering. And sometimes
    it was done as a last minute bandaid just to pass FCC radio emissions.
    :(

    --
    Bill
     
  18. James Sweet

    James Sweet Guest


    >
    > Why do you say that? aioe is based in Italy.
    >



    It has nothing to do with where it's based. Apparently you missed the very
    long thread about this a while back and the load of impostors trying to
    raise hell spamming from aioe. Most of us blocked the server entirely.
     
  19. BillW50

    BillW50 Guest

    In news:LQTHj.923$at6.237@trndny01,
    James Sweet typed on Sun, 30 Mar 2008 21:44:11 GMT:
    >> Why do you say that? aioe is based in Italy.

    >
    > It has nothing to do with where it's based. Apparently you missed the
    > very long thread about this a while back and the load of impostors
    > trying to raise hell spamming from aioe. Most of us blocked the
    > server entirely.


    Hi James! Oh yes I did miss that one. Thanks for the heads up.

    --
    Bill
     
  20. Arfa Daily

    Arfa Daily Guest

    "msg" <msg@_cybertheque.org_> wrote in message
    news:...
    > Arfa Daily wrote:
    >
    > <snip>
    >>
    >> JHC !!! Do you not understand the word "modern" ? Do you not understand
    >> the phrase "... deals with monitors of all types on a daily basis" ? I
    >> repair this stuff all day every day for a living. I have done for over 35
    >> years. I cannot remember the last time I saw a piece of kit of any
    >> description, which employed a positive ground. My friend, who owns a
    >> computer repair shop, and has done for many years, cannot remember the
    >> last time - if ever - that he saw a monitor with an external power
    >> supply, that was not negative ground with the connector sleeve as the
    >> negative connection.
    >>
    >> With so much interconnectivity between household items now, there has had
    >> to be a degree of standardisation on this issue, and it has evolved
    >> through a general concensus amongst manufacturers, that negative ground
    >> will be the convention.

    >
    > <snip>
    >
    > I have resisted commenting but can do no longer; I don't know about the
    > U.K.,
    > but I frequently encounter negative center coaxial power equipment in my
    > work. These are not monitors, but a variety of consumer and industrial
    > portable devices. When the connector is not labeled and I don't have
    > docs,
    > I will physically inspect the internal wiring or the pcb that hosts the
    > power
    > connector and also do resistance measurements between ground planes and
    > the
    > power connector contacts to determine ground. The assumption that ground
    > planes are negative is a given in most instances. As for the subjective
    > label "modern", that is a religious issue that shouldn't be a factor in
    > good electronics practice ;)
    >
    > Michael


    Michael. I'm not quite sure exactly what you are saying here. I do not doubt
    that you encounter equipment with a negative pin connection on the coaxial
    DC connector. I have not disputed this during this thread. In fact, I
    actually said in my original reply to the OP, that although these days, pin
    = "+" is the common convention, it is by no means cast in stone. I'm sure
    that even though you do have dealings with negative pin equipment, you would
    concede that positive pin is by far the more common at this point in time,
    and has been for some years. Irrespective of which pole of the connector is
    the positive one, you seem to accept that ground being negative is the "...
    given in most instances", which is what most of the controversy generated
    within the thread, has been about. So as far as I can see, we are both 'on
    the same page'.

    I don't understand what you are saying about the word "modern". It is quite
    a well defined word, and fits well, in this context, with the dictionary
    definition

    http://dictionary.reference.com/browse/modern

    particularly with the entry that refers to it being something that is "not
    obsolete". Whilst you are correct that it is a subjective word, in the case
    of electronic equipment, I would contend that most electronic engineers
    would infer something of the order of 8 -10 years to be meant, when calling
    electronic equipment "modern".

    And Bill.

    I will now explain why your contention that your method will work under all
    circumstances, is not valid. You are quite wrong with your assumption that
    all of the circuits in a piece of equipment are stacked up in parallel
    across the DC input socket. Whilst this might have been the case some years
    back, the DC connector on "modern" (infer whatever period you like from that
    word) equipment, usually connects straight into some form of internal
    ancilliary power supply, or a regulator or regulators, which are often
    switching types.

    The reasons for this are manifold, but include the fact that most modern
    equipment does not contain circuitry that runs just from 12v, which is a
    typical 'standard' value for external power unit equipment, and also
    efficiency, which dictates the regulators typically being switchers. The
    various circuits contained within the equipment, are connected to the back
    end of these regulators, and are thus not connected to the DC power socket
    in any way.

    Often, the input to this regulator circuitry, contained within special
    purpose ICs, will not produce any meaningful ohms reading, when subjected to
    the low test voltage from a multimeter. So, you are just as likely to read a
    virtual open circuit across the socket, irrespective of which way round you
    have your meter. This, in itself, will not help you to determine the
    polarity. But worse. If the unit employs a shunt protection diode, when your
    meter is connected //backwards// to the correct polarity, you will get a
    reading of 700 ohms or so, but when it is connected the //correct// way
    round, you may well read infinity or near. By your definition of how your
    system works to determine polarity, that would give you a clear indication
    of which was the correct polarity, but would actually yield the *INcorrect*
    polarity.

    As for external metalwork not being connected to the internal common ground,
    these days, that is rare. I do come across the situation sometimes, on AV
    amps, where the RCA socket sleeves are floating with respect to the chassis,
    but it is the exception rather than the rule, and is done to help alleviate
    potential ground loop issues when connecting to other equipment.

    As far as the polarity of the ground goes, I am prepared to say that in my
    considerable experience, on modern equipment designed for the consumer
    market, it is always negative. And that really is about as cast in stone as
    anything in electronic design ever is. I could of course be wrong on this,
    but if anyone wants to correct me with specific examples - remembering
    "modern" and "domestic", I'm listening, and willing to modify my position on
    it.

    I say again, that the OP asked a simple question, to which there was a
    simple answer. I don't really believe that there was any need to muddy the
    waters to the extent of all of this silly stuff that has been put forward,
    but hey - ho. I guess it all makes for an interesting life ... d;~}

    Arfa
     
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