polarity of power cord - gateway fpd1520

In ,
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

In ,
Arfa Daily typed on Sun, 30 Mar 2008 16:24:25 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Sun, 30 Mar 2008 14:23:08 GMT:
"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Fri, 28 Mar 2008 16:07:57 GMT:
"BillW50" wrote in message
. com...
In ,
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).

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

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.

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

"msg" wrote in message
...
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

In ,
Arfa Daily typed on Mon, 31 Mar 2008 00:37:00 GMT:
[...]
And Bill.

I will now explain why your contention that your method will work
under all circumstances, is not valid.

Sorry if you got that impression, but that isn't what I meant.

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.

Yes I remember.

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.

Yes but the regulators are.

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.

Yes... so if you have a high/low resistance readings, this is very
useful. If you have a low/low or a high/high, checking the resistance
isn't useful under these conditions.

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.

True, but it will not hurt anything. As the shunt will only allow about
a negative 0.7v to the rest of the unit. So unless the shunt blows, it
shouldn't ever hurt it. You can possibly damage the adapter, but it
should be protected against such anyway. But it is cheaper than the unit
it is powering anyway. ;-)

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.

Yes I agree. But thinking that way, you may fry every positive ground
you come across. If that is an acceptable risk for you and others...
well what can I say? While some risks are acceptable to me, frying
something because you had the polarity wrong just isn't one of them. LOL

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;~}

I believe having enough information to make a wise choice is far better
than bozos telling you that you have to do it this way and there are no
becauses.

--
Bill

"BillW50" wrote in message
. com...
In ,
Arfa Daily typed on Mon, 31 Mar 2008 00:37:00 GMT:
[...]
And Bill.

I will now explain why your contention that your method will work
under all circumstances, is not valid.

Sorry if you got that impression, but that isn't what I meant.

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.

Yes I remember.

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.

Yes but the regulators are.

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.

Yes... so if you have a high/low resistance readings, this is very useful.
If you have a low/low or a high/high, checking the resistance isn't useful
under these conditions.

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.

True, but it will not hurt anything. As the shunt will only allow about a
negative 0.7v to the rest of the unit. So unless the shunt blows, it
shouldn't ever hurt it. You can possibly damage the adapter, but it should
be protected against such anyway. But it is cheaper than the unit it is
powering anyway. ;-)

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.

Yes I agree. But thinking that way, you may fry every positive ground you
come across. If that is an acceptable risk for you and others... well what
can I say? While some risks are acceptable to me, frying something because
you had the polarity wrong just isn't one of them. LOL

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;~}

I believe having enough information to make a wise choice is far better
than bozos telling you that you have to do it this way and there are no
becauses.

--
Bill

Well, I guess we could go on dancing around this one for ever ...

With the circuit loads being connected to the back end of regulators that
are likely to have high input resistances with respect to the low test
voltage supplied by a multimeter, you really are unlikely to read anything
meaningful across the DC input socket. Trust me. I do this (very
successfully) for a living. Reading high-low, low-low, high-high, is
fundamentally useless to determining input polarity, unless you have a
schematic for the equipment to know what you are looking at. If you had a
schematic, you would not, of course, be trying to determine the polarity in
the first place ...

It is also not necessarily true that you will damage nothing if you do
arrive at a wrong conclusion as a result of applying your ohm-meter test to
an equipment which employs a shunt protection diode. Remember that the power
supplies for LCD TV sets and monitors, when these are external types, are
capable of supplying typically 2 to 4 amps. This is plenty enough to destroy
a typical 1 amp shunt diode, or to blow a pico or surface mount fuse, as is
typically found in such devices, or even to take out print, which is
sometimes deliberately 'necked' to provide a fuse function. Shunt protection
diodes seldom survive a reverse connection. Ask anyone who repairs CB
radios, or PMR radios, or plain old car entertainment radios.

Even if no shunt diode is used, there is still no guarantee that any
regulator device which has reverse polarity applied to it, will survive. I
have seen plenty that haven't.

I honestly don't believe that I am going to fry *any* positive grounds that
I come across, for the simple reason that on modern equipment, I just don't
come across them. They died out pretty much with germanium PNP transistors.
Obviously, if I was trying to determine the polarity of a piece of 30 year
old kit, I would take the trouble to employ different methods to do so, on
the off-chance that it might have a positive ground, but again, trust me,
positive grounds simply *aren't* encountered on modern equipment.

I hope when you refer to "bozos", you are not including me in that, as it
would cause me to take extreme offence at you. Having enough information to
make a wise choice is indeed a laudable objective, but discounting the
advice of someone who has more than 35 years declared experience in a field,
borders on stupidity. I certainly would not tell anyone that they *must* do
it this way, but if I believe, based on my considerable experience in the
repair field, that a particular method is likely to yield a correct answer
with a better than 95% certainty, then I am going to advise them of this,
which I believe is the way I approached the OP's original question, in the
first place.

Whilst there are always "becauses" as you put it, in this particular case,
their validity is negligible, for all of the reasons that I have
(painstakingly) explained over and over.

Arfa

Arfa Daily wrote:
"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



The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.

In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$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



The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

Tim wrote:
In article xTkLj.3775$bQ1.832@trndny09, says...
Arfa Daily wrote:
"zirath" wrote in message
news:0f2Hj.7616$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


The ohm meter showed something like a capacitor on the center pin (it
went to 0 and then back towards the center). The side showed no resistance.

The monitor went on briefly and then went black when plugged into the
power. Seems like it's a dud. Not sure if it's worth trying to repair it
or just return it.


Is there no little pic of the connector around where it give the info
about power? Usually there is a universal icon used that indicates
polarity, kinda like a big C around a dot. Most, but not all, coaxial
power connectors have the minus side on the outside, that way if it
touches a grounded side, it will not destroy the adapter. If the adaptor
cannot start the monitor because it is not powerful enough, it will
sometimes just flash the backlight then go off.

- Tim -

The adapter symbol shows center + and side -. It is labeled 12vdc 4a.
The monitor is 12vdc 2.5a so the adapter should have enough power.