monitor energizing computer chassis?

[jsmith2000]

I have a ViewSonic VA1938w-LED monitor. If I plug in the monitor signal cable to a desktop and the power cable to an outlet (the desktop has nothing but the monitor connected to it and it is NOT plugged in.) and check the computer chassis with a neon light tester, the light comes on, indicating the chassis is energized, albeit low voltage.

If I take another ViewSonic VA1938w-LED monitor and plug the signal cable to another desktop computer, which also has nothing connected to it except the monitor, and check it with a tester, again, the light comes on, indicating the chassis is also energized. This is a different monitor (though same brand and model), different signal cable, and different desktop. Yet, in both cases, the computer chassis are energized.

The only way I can think of for the computer chassis to be energized is the power somehow goes from the monitor through the signal cable to the desktop computer.

I wonder if this is by design or there is something wrong with the mother board or something.

 

[trents]

I'm not sure if this is related but I know that whenever I have a monitor plugged into power and turned on (with computer powered down) and I then connect the video cable to the video card port the monitor recognizes that I have done that and begins to search for a signal. The display shows it cycling through DVI, VGA and HDMI before going blank.

Have you used a multimeter to check the voltage being passed to the chassis? You should be able to check this by touching one lead to a bare metal part of the case and the other to wall socket ground.

 

[jsmith2000]

It is 0.5V between the chassis and ground.

I also checked the pins of the monitor signal cable. Everyone of them is energized. Not sure if this is normal. I wonder how the power goes from the video circuit to the chassis.

 

[trents]

When I check case to ground with power plug to PSU disconnected but monitor data cable connected I don't get any juice showing on the multimeter. My guess is something is wrong with that model of monitor. At the very least I would contact ViewSonic and make an inquiry. Having said that, .5 volts isn't going to hurt anyone or anything as long as it's not feeding into other sensitive components.

 

[caddi daddi]

somethings wrong with the monitor, don't use it.

- - - Updated - - -

In this thread you state you can feel a tingle, don't use that monitor please.

computer chassis is energized

If I plug in the power cord to a desktop, which has nothing attached to it (no mouse, no keyboard, no monitor), and check the chassis with a electric neon light tester, the light comes on, indicating the chassis is energized. There is a tingling sensation if I touch the chassis. This happens...

www.overclockers.com

 

[trents]

CD I don't see where the OP says he can feel a tingle in this thread. Am I missing something? I've been known to read and re-read stuff and still miss things. I'm not sure .5 volts is enough to produce a tingle. From what I read the OP only detects this with instrumentation. But I agree with you that something is not right. My fear would be this issue would intensify and become dangerous.

 

[trents]

It is 0.5V between the chassis and ground.

I also checked the pins of the monitor signal cable. Everyone of them is energized. Not sure if this is normal. I wonder how the power goes from the video circuit to the chassis.

A video card has an I/O bracket is typically secured to the chassis by a screw so there is a pathway for electricity to the chassis there. Onboard video ports make contact with chassis at the rear of the computer in the I/O shield area.

 

[caddi daddi]

see this thread,
http://www.overclockers.com/forums/...er-chassis-is-energized?p=8062279#post8062279


and it's not the voltee thingys that will kill you, it's the ampee thingys.

 

[Lochekey]

see this thread,
http://www.overclockers.com/forums/...er-chassis-is-energized?p=8062279#post8062279


and it's not the voltee thingys that will kill you, it's the ampee thingys.

50 milliamps is enough to stop a normal healthy heart with the threshold for some individuals being much lower.

 

[trents]

see this thread,
http://www.overclockers.com/forums/...er-chassis-is-energized?p=8062279#post8062279


and it's not the voltee thingys that will kill you, it's the ampee thingys.

Isn't it both together, amperage and voltage that determine whether electricity is dangerous? It's the total power I think.

 

[HankB]

Isn't it both together, amperage and voltage that determine whether electricity is dangerous? It's the total power I think.

V = I * R

V = Volts
I = Current
R = resistance.

Solving for R, V / I = R

Given V = 0.5V, I = .00005A => 0.5 / 0.00005 = 10000 ohm (10 K ohm.)

My Fluke measures about 1 Mohm from one hand to the other. That's 1.000,000 ohms. 0.5V will drive

0.5 / 1000000 = .0000005 Amps

Seems unlikely that 0,5V is going to be dangerous.

General practice in industry (when I worked in the steel industry) was up to 50V did not require special precautions. And IIRC the old POTS worked at about 25V to accommodate this.

 

[Lochekey]

Voltage plays a factor as well location of the power source but only insofar as how much voltage does it take to overcome the bodies resistance.

For example it would take a stronger voltage to pass from hand to hand than from front to back of the thoracic cavity.

Probably one of the worse shocks I have experienced was from an old telephone line ringing while I was working with the wires. The small gauge wires had penetrated my skin and where in direct contact with the underlying tissue of either hand. Let me tell you that was not pleasant.

 

[||Console||]

Voltage plays a factor as well location of the power source but only insofar as how much voltage does it take to overcome the bodies resistance.

For example it would take a stronger voltage to pass from hand to hand than from front to back of the thoracic cavity.

Probably one of the worse shocks I have experienced was from an old telephone line ringing while I was working with the wires. The small gauge wires had penetrated my skin and where in direct contact with the underlying tissue of either hand. Let me tell you that was not pleasant.

The old phone line was DC =) . DC hurts

We were told the same 50miliamps (in perfect conditions ) as you but in practice it is its way higher . We were always told that it is amps not voltage that kills . Thats how you survive a lighting or tazer , high voltage no amps .

I have been a sparky for 10 years now , I have had my share of blasts from 120v-600v (477 hurt the most IMO) , I don't normally notice 120v at first really I assume its the edge of the Box first that scratched me its the second and third tingle that lets me know its live .

 

[Lochekey]

The old phone line was DC =) . DC hurts

We were told the same 50miliamps (in perfect conditions ) as you but in practice it is its way higher . We were always told that it is amps not voltage that kills . Thats how you survive a lighting or tazer , high voltage no amps .

I have been a sparky for 10 years now , I have had my share of blasts from 120v-600v (477 hurt the most IMO) , I don't normally notice 120v at first really I assume its the edge of the Box first that scratched me its the second and third tingle that lets me know its live .

I have been out of the wiring game for a few years now but I know what you mean by the 120-volt circuits. It was always like a buzzing in the skin that was not quite perceptible. I agree 480 hurts big time but still to this day I remember that gosh darn phone line. I know the last place I worked we avoided using any DC equipment unless it was absolutely necessary due to the safety factor.

 

[||Console||]

I know a guy that was stripping a phone line with his teeth when the phone rang =) he says it was his worse shock as well .

 

[HankB]

I know a guy that was stripping a phone line with his teeth when the phone rang =) he says it was his worse shock as well .

Isn't that where the expression "ring his bell" came from.