LCD monitor electric problem

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Cyrille

Something strange is happening to my LCD monitor (Acer AL1511): The
ground of the VGA cable carry 110 volts ! I noticed the problem while
switching PCI cards and got electric shock when touching the computer
case or any metal parts even the power cable was unplugged. The only
thing plugged in was the VGA cable of the monitor so I unplugged it and
no more electric shock. When I touch the ground part of the VGA
connector (unplugged from the computer) I get the 110 volts electric
shock. Is my monitor suddenly broke down or could it only be the cable?
Thanks for any idea/suggestion!
 
This could be caused due to the grounding issues in your house. I had
similar problems but when i fixed my Computer socket directly to a
ground I had no problems since. I hope this helps you out
 
Cyrille said:
Something strange is happening to my LCD monitor (Acer AL1511): The
ground of the VGA cable carry 110 volts ! I noticed the problem while
switching PCI cards and got electric shock when touching the computer
case or any metal parts even the power cable was unplugged. The only
thing plugged in was the VGA cable of the monitor so I unplugged it and
no more electric shock. When I touch the ground part of the VGA
connector (unplugged from the computer) I get the 110 volts electric
shock. Is my monitor suddenly broke down or could it only be the cable?
Thanks for any idea/suggestion!
Click to expand...

Well, I don't know how you are going to fix this, but I can
give you a hypothesis.

First, we'll start with the only schematic I know of, showing
the innards of an ATX supply. The power conversion circuit inside
your LCD monitor will not be exactly the same, but all supplies
share some common concepts.

http://www.pavouk.comp.cz/hw/en_atxps.html

The circuit consists of a primary and a secondary. The primary
side uses 120V or 240VAC. The secondary side has DC voltages,
used to power the logic ICs, backlight and so on. The output
transformer isolates the 120V from the low voltage DC outputs.
(And example of a transformer in the diagram, is a long black
bar with coil symbols lined up next to it. The identifier "T3"
is printed next to it, on the upper right hand side of the
diagram.)
--- AC ---- Xfrm --- Rectifiers --- DC --->
Click to expand...

Now, on the AC side, the high voltage AC is converted to high
voltage DC, and a switching circuit commutates the high voltage
at a high frequency, and applies that signal to the transformer.
The conversion process makes noise, and this noise can go back
down the power supply cable and upset broadcast television
reception.

To reduce the interference, a filter is placed in front of the
AC side.
---- filter ---- AC ---- Xfmr... DC --->
Click to expand...
|
|
x-------+------------------------------------> safety gnd, COM
on 20 pin connector

The job of the filter, is to redirect noise down into the safety
ground. The noise would flow down and to the left, in the above
diagram. It would go to the third prong of your AC cord, shown
with the "x" above.

Now, the filter doesn't know the difference between switching
harmonics extending up past 30MHz, and the 60Hz current flowing
from the wall. Not only does the filter shunt the noise current
moving from right to left, downward and out through the "x". It
also redirects wall current, flowing from ">" downward and
to the left as well. This is termed the "leakage current" and
every device equipped with a filter, has a specification for
how much leakage, _by design_, flows into the safety ground.
The leakage is unavoidable, and is controlled to what is
considered a safe level.

(Some of this is discussed here.)
http://www.elpac.com/resources/emiwp.html

In the reference schematic I provided above, the filter
components are C4 (a capacitor), T5 (a common mode choke),
and capacitors C2 and C3. The basic filter form is called
a "PI filter", for the Greek letter PI. The letter PI is
two vertical bars, with a bar across the top. The choke T5
and the caps, form that same PI shaped letter, and that is
why it is called a PI filter. Notice how, in the schematic,
the tap point between C2 and C3 goes to the shield. That
is where the leakage could come from.

Now, let's modify the above figure. I'm going to cut the green
safety ground wire in the line cord. Or break off the third prong.
---- filter ---- AC ---- Xfmr... DC --->
Click to expand...
|
|
// --+------------------------------------> safety gnd, COM
on 20 pin connector

Now that current that used to be safely disposed of, in the safety
ground, has no place to go. The computer case and every I/O
connector on the computer, have some fraction of 120V riding on
them. As soon as the unwary user touches the chassis of the LCD
or the shield on an I/O connector, they get a tingling as the
leakage current flows through them, on its way to ground. (If
the VGA cable is fully connected from LCD to computer, the leakage
current flows down the green ground wire on the computer power
cord, and the computer+LCD is safe to touch. It is just when
the LCD is by itself, you get the shock.)

The thing is, your product has a removable line cord. I would
try another cord, and see if the problem stops. But if that doesn't
solve it, either seek professional help, or buy a new one. As I
understand it, some of those cold cathode backlights use high
voltage, and you really don't want to be poking around in there.
While all well designed high voltage circuits, have bleeder
resistors, nobody in the trade relies on a bleeder resistor
to keep them safe. Bleeders can fail, and bleeders can age
due to being under stress from the high voltage. It is better
to assume all high voltage circuits are dangerous, than to find
out the hard way. I've only been thrown across a room once
by high voltage - I learn pretty fast, once I pick myself
up off the floor and dust myself off :-(

A technician would check the filter components, to see if
any of them have failed. Or check to see if the safety
ground is broken inside the circuit board somewhere.
These components would not necessarily be something you
could find an exact replacement for, at Radio Shack.

Paul
 
I found the source of the problem. It doesn't come from my LCD monitor
but from my UPS (Delta)! How can this happen? the UPS is sending 110v
on the ground prong! It is supposed to protect the devices plugged into
it! (not the other way around). It shoudn't work that way I thing even
if the UPS is not grounded. I'm not electrician, but it sounds like
common sense.
Any comments on this is welcome!
 
I found the source of the problem. It doesn't come from my LCD monitor
but from my UPS (Delta)! How can this happen? the UPS is sending 110v
on the ground prong! It is supposed to protect the devices plugged into
it! (not the other way around). It shoudn't work that way I thing even
if the UPS is not grounded. I'm not electrician, but it sounds like
common sense.
Click to expand...

Is the UPS grounded on the utility side?


--

"What the American people have seen is this incredible
disparity in which those people who had cars and money
got out and those people who were impoverished drowned."
-- Ted Kennedy on Hurricane Katrina

"Ditto"
-- Mary Jo Kopechne
 
I found the source of the problem. It doesn't come from my LCD monitor
but from my UPS (Delta)!
Click to expand...

Is this really a Delta UPS, or do you mean a Delta monitor
power supply, a brick type supply that plugs into a wall
outlet (or then an UPS)?

It is common for a small switching power supply to have it's
DC ground shared with AC ground. Are you certain your
outlets are wired properly?
How can this happen? the UPS is sending 110v
on the ground prong!
Click to expand...

It's not really "sending" anything, most likely, it's just
that your power is 110V higher than ground. If your AC
outlet is not keyed properly or misinstalled, you might
check it with an AC outlet checker o
It is supposed to protect the devices plugged into
it! (not the other way around). It shoudn't work that way I thing even
if the UPS is not grounded. I'm not electrician, but it sounds like
common sense.
Any comments on this is welcome!
Click to expand...

Is it definitely an UPS? UPS is a large power source with
it's own battery inside and several outlets on it. Perhaps
you know this and you were right all along, but I question
that it was an UPS at all because Delta is a major
manufacturer of small switching power supplies but not of
any consumer UPS (at least not here in the US).

If it is an UPS, is it grounded?
If it isn't, whatever-it-is, is it grounded, does it have
the ground plug on the power cord and are you certain the
outlet is grounded properly?

Are BOTH the computer and this other Delta thing, plugged
into the same outlet? Is the outlet keyed and is the Delta
plug keyed so it will only insert one direction?
 
The UPS has a 3 prongs plug but since the wall outlet has only two (not
grounded), actually the UPS is not grounded. The building I live is
very old (no grounded outlets). I was thinking of running a cable
attached to a water pipe to get a ground.
Every outlets on the UPS (where connect the PC and other devices) are 3
prongs type (hot/neutral/ground)
 
Yes it is an UPS (Delta brand name). It has it's own battery and
provides power when there's a power failure. It's a big blue box with 4
AC outlets on one side (surge section) and 4 AC outlets on the other
side (ups section). Only the ups section provides power when power is
down. I live in Taiwan and I bought it there.
Every outlets and plugs on the UPS is 3 prongs type
(hot/neutral/ground). But the wall outlet of my house is only two (no
ground because old building). So the UPS is plugged into a non grounded
outlet (via an adapter). I was thinking of running a ground cable
attached to a water pipe to get everything grounded. But even though,
will that solve the problem? The computer is plugged into the Delta
UPS. I tested the outlet: the large slot is the hot and the small slot
is the neutral (cold). Every outlets is keyed. Do you think my UPS has
problem or is this normal when the UPS is plugged into a non grounded
outlet?
 
Yes it is an UPS (Delta brand name). It has it's own battery and
provides power when there's a power failure. It's a big blue box with 4
AC outlets on one side (surge section) and 4 AC outlets on the other
side (ups section). Only the ups section provides power when power is
down. I live in Taiwan and I bought it there.
Every outlets and plugs on the UPS is 3 prongs type
(hot/neutral/ground). But the wall outlet of my house is only two (no
ground because old building). So the UPS is plugged into a non grounded
outlet (via an adapter).
Click to expand...

I think you need to see if the UPS plug is in the outlet the
wrong way around the wrong polarity and consider having an
electrician take a look at the wiring and install a keyed
and grounded outlet. I plead ignorant to Taiwanese AC
wiring though, you would be better advised by someone who is
experienced with it before proceeding.
 
Cyrille said:
The UPS has a 3 prongs plug but since the wall outlet has only two (not
grounded), actually the UPS is not grounded. The building I live is
very old (no grounded outlets). I was thinking of running a cable
attached to a water pipe to get a ground.
Every outlets on the UPS (where connect the PC and other devices) are 3
prongs type (hot/neutral/ground)
Click to expand...

In the city I used to live in, I think I phoned the city
inspectors to ask them a question about wiring. Perhaps you
could phone someone like that, or phone an electrician, and
see what the code is in your area. (Use a pay phone, if you
want to remain anonymous.) When it comes to electricity,
you don't want to do anything which will void your fire
insurance. It could be, that a cold water pipe is not
considered good enough.

Paul
 
I think you need to see if the UPS plug is in the outlet the
wrong way around the wrong polarity
Click to expand...

He is not going to know which side of the two-prong plus is ground ...
and consider having an
electrician take a look at the wiring and install a keyed
and grounded outlet.
Click to expand...

.... so he needs to follow your advice and get professional help.

This incident shows why you should never test a UPS by pulling the
utility power cord. If you do, you will lose your ground. You can test
it by tripping the circuit breaker, which will not interrupt the
ground.


--

"What the American people have seen is this incredible
disparity in which those people who had cars and money
got out and those people who were impoverished drowned."
-- Ted Kennedy on Hurricane Katrina

"Ditto"
-- Mary Jo Kopechne
 
Cold water pipe is not acceptable for any grounding. The
only electric wire connection to a water pipe should be one to
remove electricity from that water pipe. This should be
woefully obvious. Connect what could be a live wire to the
same pipes touches by a wet human in shower or bath? Only
someone with no respect for human life would do that.

Essential to that system is that all computer system
components connect to the same safety ground - that third
prong on each plug. This so that a failing component even does
not cause LCD monitor to damage computer video controller.

Meanwhile, if 110 volts in on the safety ground, well, 100
volts relative to what? Voltage does not exist in a vapor.
Voltage exists between two points. What are the two points?

"It is supposed to protect the devices plugged into it!" is a
widespread myth. The plug-in UPS does one basic function.
Switch over to batteries when AC mains are insufficient. To
get those other functions, one installed a building wide UPS.

AC mains connect direct to appliances through UPS when not
in battery backup mode. And still, that safety ground must
connect all plugs and receptacles together no matter what mode
the UPS is in. That means even a UPS must have nothing but
electric wires interconnecting every plug's third prong. No
filters. No isolation. All safety grounds must be connected
together for human safety reasons.

So what two points have a 110 volt difference? And this
voltage was measured by what?
 
I understand your point about grounding. Of course water pipe grounding
is not the right solution. This is a temporary solution until a real
ground is wired. For the safety I don't think water pipe grounding can
harm anyone because if any electricity is going through the water pipe
it will also go to the earth anyway (unless the water pipe is not
connected to the earth or not deep enough).
The way I've tested the ground issue is simple: I use a multimeter set
on voltage reading. I plug one end of the multimeter into the groud
hole of one of the UPS outlets and I hold the other end in my hand to
have a pseudo "cold" or "neutral" point. My floor is tiled (good earth
contact) and I'm bare foot to get more conductivity in order to have a
more accurate reading. The reading display a value between 90-105 volts
The two points that have (more or less) 110 v difference is the ground
wire of the UPS outlets (ground hole) and the earth.
Normally it should show a value of 0 volt. Because the ground is
interconnected to every devices that have a 3 prongs plug, it can be
dangerous because every grounded part of those devices carry 110v (like
the computer case for example)

p.s. Sorry for my bad english (I'm not very familiar with those
technical terms). I hope this is clear enough to understand
 
First, reason why the NEC does not approve of any safety
grounding to water pipes is that, contrary to your
assumptions, the dumping of electricity is dangerous to humans
in a shower or bath. Made most dangerous when natural
protection of human body to electrical shock literally
disappears when that body is wet. Never - even temporarily -
safety ground anything to water pipes. Your assumptions about
it being safe temporarily are totally incorrect. Never safety
ground to water pipes.

Second, human safety can be created by replacing that wall
receptacle with a GFCI receptacle. A solution stated
specifically in the code. For human safety from electrical
shocks, install the GFCI and put that code required label on
that says, "No Equipment Ground".

Third, you probably have measured normal leakage.
Everything leaks electricity. 110 volts at only 10 microamps
is completely safe - normal leakage. Those same leaking 10
microamps would measure near zero volts if the safety ground
existed. Normally I would have expected more like 65 volts.
But the way you took measurements changes previous replies.

Fourth, as stated earlier, all computer components should
have safety ground prongs connected together. This because
otherwise one layer of transistor protection between those
components would be missing.

Again, a worst solution would be to safety ground to water
pipes. The code does not oppose this only to sound nice or
proper. Grounding appliances is taboo for specific and
bluntly obvious reasons - including some I did not mention.
 
I understand about the grouding safety issue. But concerning my Ups, you
think the leakage is normal? Notice that I don't have that kind of leakage
when the UPS is unplugged and when the appliances (computer, monitor and so
on) are plugged directly into the power bar or the wall outlet.
So my question is: Do you think my UPS is malfunctionning or defective?

Thanks for your feedback!
Cyrille
 
To answer your question, determine how much current is
leaking from that UPS. If UPS connects into some other three
prong (properly connected to breaker box safety ground)
receptacle and it trips the circuit breaker, then UPS is
definitely broken. If you plug the into a GFCIed outlet that
has the equipment ground, and if the UPS does not trip the
GFCI, then the UPS is probably OK - leakage current is below
5000 microamps. However UPS should be below 150 microamps
which is where meter makes a better measurement. But I would
do these tests first so that too much current does not
'accidentally' go through and damage meter.

Do final test with the meter. But that means meter in
current mode must connect between UPS and breaker box ground.
IOW the safety ground connection must be through something
with low resistance which a tile floor does not provide.
Water pipe might be good here for a temporary test when no one
is at risk. This assumes pipes are all metal all the way back
to breaker box ground and no one is taking a shower. Another
technique is to run a three wire extension cord to some remote
receptacle that is properly safety grounded.

UPS must not create massive leakage when plug is connected
properly AND when AC plug is reversed. Last test to confirm
leakage is not different when plug is reversed. Reversing
plug should not create excessive leakage.
 
I checked the breaker box and it seems to have one (and only) green
wire that could be the ground. I used the voltmeter to check between
the red wire and the green one and it reads around 110v. So the green
wire could be either the ground or neutral.
To make sure, how can I test that? I took a digital picture of the
breaker box. I could send it to you by e-mail if you wish to take a
look at it (how's the wires are connected). It's seems like in Taiwan,
electrical code is not as strict as in the US or Europe. Even polarity
for the outlets is up to the electrician's mood at the time!
Thanks again for your help!
 
By breaker box, I assume it is the building breaker box (in
US or Taiwan?). Throughout the world, green is the color of a
safety ground wire. Solid green in the US. Green with yellow
strip internationally. That green wire must connect to
neutral bus bar inside breaker box. IOW it must only carry
current when it is shorting out a fault (or carrying away
leakage currents).

You have a breaker box to measure to. Take a jumper wire
from the UPS safety ground prong to the breaker box cover - a
metal surface. Extension cords can be used to make this
connection. This test should not trip any breakers. This
test only to verify excessive current does not harm meter in
this next test. Then use meter to measure current from that
safety ground prong to breaker box. That current should be in
the microamps region.

BTW, voltage from breaker box cover to that tile floor
should be zero. Just another test you might perform; might
provide a surprise fact.

In Taiwan, the 'get it done no matter what' attitude is too
acceptable. Reason why a whole and new IC foundry for UMC
burned - end to end. Failures happen for good reason. Your
concern for that possible 'hot' safety ground is quite
admirable and responsible - especially to those who will use
that UPS later.
 
Let's assume the breaker box doesn't trip while connecting the UPS'
ground prong to the breaker box cover, I won't be able to mesure the
current with my multimeter because this one can only mesure DC Amps and
not AC Amps. Is there other ways to mesure that?
BTW, the breaker box is inside my appartment (in Taiwan)
 
Meter only does AC volts. Forgot some meters are made that
way. Get some resistors from Radio Shack or equivalent. For
example, a 10000 ohm (10K ohm) quarter or half watt resistor
can be put in series with the 'safety prong to breaker box
cover' jumper wire. 110 volts across the 10000 ohm resistor
would conduct 0.1 amps. Don't wait too many seconds because
this resistor will get hot - eventually burn up - if leakage
current is excessive. However, if this resistor does not get
hot and if voltage across this resistor is much less than 110
volts, then we know the leakage current is not a direct short
to the hot 110 volt wire.

BTW, color bands on a 10K resistor would be brown, black,
orange.

So how much is the leakage? Voltage across the resistor
divided by 10 is number of leaking milliamps. For example,
with that 10K resistor between UPS safety prong and breaker
box cover, if voltage on that resistor is 30 volts, then
leakage would be three milliamps. Too much leakage but not
extremely dangerous. I just would not have a three milliamps
leakage where wet humans could touch it. Otherwise, no
serious safety problem. (If resistor measures 110 volts, then
resistor is dissipating over 1 watt - it will not last long.)

Now if that measured voltage is seventy or less, then replace
the 10K ohm resistor with a 100 ohm (color bands are brown,
black, brown) quarter or half watt resistor. Measure this
voltage. Voltage times ten would be the leakage current.
Sometimes this might measure .3 volts if leakage current
remains 3 milliamps. However sometimes the leakage current
may increase. That 100 ohm resistor voltage might measure 0.8
volts meaning the leakage current is a higher 8 milliamps.
Therefore we have a better idea of what to look for as a
leaking internal component.

If current leakage was 150 microamps or less, then voltage
on the 10K ohm resistor will be 1.5 volts or less. Voltage on
100 ohm resistor is less than .1 volts. 150 microamps is
acceptable. 150 uamps would create 110 volts when measured to
the tile floor, would give UPS a 'funny' feel to human touch,
is not enough to trip a GFCI, and is not considered human
dangerous.

A 1.5 volts (or less) on 10K resistor means we need not
worry about that 110 'floating' volts as long as all computer
components interconnect to a common safety ground (ie the same
power strip). A safety ground connects to all computer
peripherals but not connected back to breaker box due to a two
prong wall receptacle.

BTW, e-mail that breaker box picture. Curious what you have
there. Never saw the insides of a Taiwan breaker box.
 
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