Laptop Has a Buzz and Lights Up with Test Pen

You can get a static buildup with no ground.....

I had a dog once that liked to bite electrical cords. At some point, he decided to quit escalating with that strategy. But then he ran under a bus he was chasing....

??

I had a dog 'Red' that like to chew on things.

One cold December day, I plugged in an electrical cord that I knew was plugged in an outlet on the other end. and nothing.

I tracked the cord back to the other room and 'Red' was in a poised position just like the Egyptian Sphinx. I said, 'Hey there, what's you doing boy?" He didn't move, I went a little closer, and he had the electrical cord going right through his mouth. And he was froze in that Sphinx prone position.

As sad as it was, it still was kinda funny.

I don't know the wiring standards of your country, but to me it sounds like "the certain wall outlets" might have the hot and neutral reversed.

I totally agree with you on this one. The part that I find puzzling is that 'most' laptop power supplies have isolated outputs, i.e. neither positive nor negative power supply output is tied to the 'neutral' (or grounded conductor in NEC parlance.) Usually the galvanic isolation between line voltage and the output is 3 kV or more.

In the case of 230V circuits, (not knowing the country's wiring codes) I would suspect that neither of the power lines are 'grounded conductors' but these days, who knows?

I think there maybe something else connected in the system (external monitor, printer, etc.) that is feeding line power back into the signal reference/return path.

In most country the neutral is grounded at some point, but depending upon the distance to laptop and the unbalance in the loads of the 3 phases of the mains transformer, the neutral can get a far higher voltage on it than 0.

Local code must be checked for the allowed differences.....

What about the many countries where this happens at almost every socket?

For example, unpolarised plugs and sockets are all over europe, and I believe they used to be standard in the USA some years ago......if not still.....

Only countries like the UK and some of its dominions have polarised plugs and a fuse in each plug, which is i the phase line.

But of course, the installing electrician must still do a good job too.

For my UK built caravan, as I connect it to the mains on our travels around Europe, I have a special plug that checks that the phase is on the correct "leg", I simply leave it plugged into a socket that is easily seen!!

Swapping the European connector around, reverses the position of phase and neutral easily.

It's the lack of a ground (earth) path as previously mentioned. But it's not the line source isolation that's the problem, it's the common mode noise created by the power supply and power supply boards inside of the computer for the various systems inside. The main power supply is often that external "brick" device and it is a Switch Mode Power Supply. But inside, there are several separate DC to DC power supplies on things like the video driver, communications adaptors, sound canards etc. all of them use PWM for voltage control, and the high speed transistor switching creates common mode noise. Without a path to ground, that builds up on the chassis and when you touch it, or the capacitive test pen voltage sensor gets near, the brief discharge is the place that charge can dissipate.

Take two of these, apply liberally to each hand before using laptops.

Call me in the morning.

That will be $50.00 USD.

Its AC capacitive "leakage", and probably only on poor quality power supplies that purport to double insulated, but are not.

It might prove interesting to see if the ones where it happens are conventional power supplies or switched mode. Which are more efficient, but there are "direct" paths between the mains input and the DC output......but even then, well designed ones should not cause shocks.....

Its unlikely to kill anyone who is at least reasonably fit, and the level of the voltage can be easily measured with a digital voltmeter between say the VGA ground and the mains ground.

Local electrical code might have some information as to the maximum voltage allowed in such cases.

It can get dangerous (I am told) when say two laptops are on two different legs of the mains transformers.....and your fingers manage to touch both VGA connectors at the same time, but I have never ever experienced that myself, so it might be merely "hearsay".....

Laptop supplies with only a 2 pin cable (as you have found out!) are likely to have the problem, if poorly made, as I have experienced, as are Sat receivers with 2 pin connections I have found....but it gets "grounded" when the SAT coax cable gets connected, as is no more apparent.....

I would appreciate more learned opinions on this phenomena.

To prevent you from getting an electrical shock, as a permanent solution you may need to use an isolation transformer for your laptop!

As a temporary solution you may try reversing the way you plug the power cord to the wall! This approach is only possible if the laptop power cord has a Non-polarized plug??

Tried that, but the same phenomena persists.

Then go for an isolation transformer solution approach, if you want to continue using your present set up?

Typically laptops has its own dedicated AC adaptor /power supply to convert your line voltage to a lower DC battery voltage... In which case you have your vga monitor directly powered by its own power supply? It may be a situation where the problem is coming from that monitor and where / how it is powered?

you need to provide more info on how the system is set up/ configured?

With the various comments already posted, most bringing up valid explanations, it would be interesting to get more detail on the certain wall outlets and the certain laptops.

As already mentioned, poorly engineered or compromised power supplies, leaky or floating building wiring, all contributing to charging the capacitive coupling between you and the power system is the likely solution, but it would be interesting to know if there is one or multiple sources.

Thanks for all the feedback. I was hoping that this was a well-known situation with a well-known remedy.

I don't have time to methodically try out different laptops at different locations to clearly isolate the different scenarios.

Let's leave it as it is.

The problem has been explained to you.

If you can't understand what the problem is, buy a pair of gloves.

You do need to check, as I previously mentioned, the AC voltage difference between the shell of the VGA connector and AC safety ground. You may even find its the same/similar to the AC voltage difference between AC safety ground and neutral. rebalancing of the AC loads on the fusebox may be required.

Also check local code for allowed voltage differences.

There is also a possibility that "certain" models of laptop power supply are causing the problem, even from the same type of laptop. I generally recommend 3 wire AC in versions to be safer and cleaner.....but that may not always be easy to find.....

Furthermore, just to be safe, maybe a master electrician should be asked to check out the electrical system for correct installation. He should let you know what voltage differences there are between neutral and ground around the building IN THE MIDDLE OF THE WORKING DAY! And out of it as well......if you cannot do this safely yourself.

There might even be an insurance issue if its not a certified installation.

Maybe, as already mentioned, some isolation transformers could be put to good use, if code shows a safety issue or its just uncomfortable for users......

Something seems weird here: I have never seen a laptop plug directly into AC line power; there is always a converter to something like 9-12 VDC.

If that is not the case, then you may have some condition such as tin solder whiskers creating a connection between normally grounded and ungrounded components. Only a close internal inspection will show if that is occurring.