Electric shock from T43

[jgiam]

I've been getting electric shocks from my T43 on and off. I get the shocks mostly at the top edge of the LCD screen, especially the two corners. Sometimes they can get pretty painful, like a needle pricking me, and cause me no end of irritation when I accidentally touch the edge/corner.

However, this does not happen all the time, and I absolutely cannot pinpoint when it happens. Unlike this thread, I hardly plug peripherals into my T43. Usually all I have is a mouse and a LAN cable plugged in. But I have also gotten shocked without those plugged in.

Because my warranty is ending in under a month, I sent my laptop in two days ago. This morning, I received a call from IBM telling me that they did a thorough check and did not find any problem, nor did they find the source of the shock. The engineer suggested that some people might be more sensitive and feel these "shocks" more, as if I were imagining the shocks.

As my Thinkpad comes with on-site warranty, I am considering waiting till it starts shocking me again, and then calling for on-site service. Hrmph.

While I understand it may be hard to diagnose this problem, the nonchalent attitude of the engineer kinda irked me. To think I was about to blog about their wonderful customer service.

I suspect it might be an AC adapter fault. Does anyone have any other suggestions that I can check out?

Thanks in advance

[Tim M]

The output of the AC adapter is 16 VDC, which would not cause shocks under normal circumstances. If there were a serious fault, it would be likely that there would be damage to the computer.

Could it be static electricity? Have you been walking on a carpet or shuffling your feet before touching the ThinkPad and experiencing these shocks? Is the humidity particularly low in your location when these shocks occur? When the air is dry, I regularly get an ESD shock when touching the laptop.

[sb102]

The output of the AC adapter is 16 VDC, which would not cause shocks under normal circumstances. If there were a serious fault, it would be likely that there would be damage to the computer.

This is totaly NOT TRUE. Since this is an impulse charging unit, the risk of getting electrical shocks could be possible, as the construction of the unit is mate in a way that does not galvanicaly isolate it from the AC voltage. The notebook may run normaly, but the Judging by the symptoms I say that some of the capacitors might be damaged or there is a problem with the grounding in the AC adaptor. The only way to check wether the shocks are caused by AC voltage is to get a special flated screwdriver with a "neon" light that electrics use to check if there is a flow of AC current - you can buy it in every hardware store. All you have to do is to touch the powered-on notebook in the place where you got shockedand touch the top of the screwdriver with your thumb. If the light goes on and stays that way, this means that this is AC current. You will need to replace the AC adaptor.

Then go to that so called "engenieer" and tell him, that he risked your life and you will accuse him for that in court. That ougt to do the trick

[jgiam]

Thanks for the replies.

The output of the AC adapter is 16 VDC, which would not cause shocks under normal circumstances. If there were a serious fault, it would be likely that there would be damage to the computer.

Could it be static electricity? Have you been walking on a carpet or shuffling your feet before touching the ThinkPad and experiencing these shocks? Is the humidity particularly low in your location when these shocks occur? When the air is dry, I regularly get an ESD shock when touching the laptop.

I live in Singapore, which has average humidity of 80%. I doubt its static electricity as it isn't a "discharge" kind of feeling, but if I leave my finger there, I keep feeling the "needle prick". Also, this has happened at home as well as outside.

This is totaly NOT TRUE. Since this is an impulse charging unit, the risk of getting electrical shocks could be possible, as the construction of the unit is mate in a way that does not galvanicaly isolate it from the AC voltage. The notebook may run normaly, but the Judging by the symptoms I say that some of the capacitors might be damaged or there is a problem with the grounding in the AC adaptor. The only way to check wether the shocks are caused by AC voltage is to get a special flated screwdriver with a "neon" light that electrics use to check if there is a flow of AC current - you can buy it in every hardware store. All you have to do is to touch the powered-on notebook in the place where you got shockedand touch the top of the screwdriver with your thumb. If the light goes on and stays that way, this means that this is AC current. You will need to replace the AC adaptor.

Then go to that so called "engenieer" and tell him, that he risked your life and you will accuse him for that in court. That ougt to do the trick

For what its worth, we use the UK-style three-pin plug here. I've tried using a "test pen" (is that what its called?) but it didn't light up.

Finally, to be honest, if they can't find any specific fault, I don't know what else they can do other than replacing the entire laptop. :\

[Rick Aguinaldo]

The electric shock you described can happen if there is a leak from the high voltage side of the inverter circuit, the one that feeds the fluorescent back light of the lcd panel. In my case (a 600 lcd panel) I found a nick in the insulation of one of the wires to the the fluorescent tube backlight where it enters the lcd panel. It must have been causing an intermittent short to the frame of the lcd panel giving the electric shocks. A heatshrink sleeve repair on the cut solved the problem.

[rkawakami]

Should be next to impossible to receive a constant shock when the laptop is NOT plugged into an AC adapter. The only thing that I can think of which might cause this to happen would be the output from the inverter in contact to the lid assembly. And even then, you still need a path from your body to earth ground before you would feel anything.

If you notice you are only getting shocked when the laptop is plugged into an AC adapter, then three things are possible:

- the electrical outlet (the "mains") is not wired correctly; "hot ground" or "hot neutral"
- the AC adapter has a fault (or is designed) whereby the DC output is not isolated from the AC lines
- both of those things

The hot-ground or hot-neutral problem should be easy to test using something like this:

http://www.toolking.com/products/681000 ... se=400-029

I would assume that this type of tester is available with the proper pin arrangement for your country.

edit: Nosed out by Rick as I was looking for a BS 1363 tester but didn't find one .

[sb102]

To, be honest, I don't know what a 'test pen' is. For tests I use this:

http://www.pronar.com.pl/katalog-old/im ... 828813.jpg

It has a very simple construction and it works very well for situations like that.

Now back to the point: you didn't mention if you got shocket when the notebook was powered with bateries. If so, than this would be the inverter, just like Rick Aguinaldo pointed. Now if this occurs only when plugged into AC adapter, than I would go with my idea. I also suspect that when your notebook was in hands of that IBM technician, he didn't used your AC adapter. That is why he didn't noticed the problem.

[Tim M]

The output of the AC adapter is 16 VDC, which would not cause shocks under normal circumstances. If there were a serious fault, it would be likely that there would be damage to the computer.

This is totaly NOT TRUE. Since this is an impulse charging unit, the risk of getting electrical shocks could be possible, as the construction of the unit is mate in a way that does not galvanicaly isolate it from the AC voltage. The notebook may run normaly, but the Judging by the symptoms I say that some of the capacitors might be damaged or there is a problem with the grounding in the AC adaptor.

Interesting. Can you explain more about this lack of "galvanic" isolation as my impression of the charger design was different. My understanding was that the unit was double-insulated to prevent direct passage of AC. Some sort of inductive or capacitive leak is possible, but I would expect other symptoms with the laptop.

Given that the OP states that the relative humidity is high, I'd agree with others that the inverter for the LCD backlight might be faulty. Current might be passing to the metal enclosure of the LCD panel and dissipating through the top of the lid. An easy check would be to press the small LCD switch with a pen while touching the lid and seeing if the shock disappears.

[sb102]

Interesting. Can you explain more about this lack of "galvanic" isolation as my impression of the charger design was different. My understanding was that the unit was double-insulated to prevent direct passage of AC. Some sort of inductive or capacitive leak is possible, but I would expect other symptoms with the laptop.

I don't know how do you imagine a charger design, but there are two main types of them: impulse and with the use of a transformer. The term "galvanic insulation" is connected with the second type of the power suply and is very closely connected with the transformer. It cosists of a pair of windings made from a thin copper cable that are placed on a ferrite core. when a current passes through the primary winding (the one connected to the high voltage home instalation) it generates an electromagnetic field. This field causes a flow of current in the secondary wiring - this will have a significantly smaller value than in the primary. And since there is no direct connection between the primary and secondary wirings, those two are in some way insulated. So, when a leakage will happen in the powered device the value of the leakage current will not cross the value of the one in the secondary wiring. As for the impulse power suplies, mainly used to deliver stable voltages to computers (the example: the Power Brick in our thinkpads):although they are lighter and more effitient than those with a transformer they are connected directly to the power line - when there is a leakage, its value can reach the one in the power line. And since I'm a pessimist and got shocked two times (I am not counting the electrostatic shocks that I recieved in my life) by a faulty grounding of a device, I opt for the problems with grounding (just as jgiam said - those are very painful).[/b]

[Tim M]

^ Thanks for the information; I am less familiar with impulse chargers. I should note that my ThinkPad charger has no ground pin and bears a double-insulation marking. I am not clear if the OP's charger has a different design with a ground (earth) prong. If so, there could be a ground fault in the charger.

That said, I still think an LCD lamp inverter issue might be the cause.

[fasterbybike]

Can you explain more about this lack of "galvanic" isolation as my impression of the charger design was different. My understanding was that the unit was double-insulated to prevent direct passage of AC.

Laptop chargers use the switch mode power supply design and are galvanically isolated. The internal transformer operates using pulsed high voltage DC, rather than converting the supply AC directly. (This is why they can use a wide range of supply voltages - typically 90-250VAC).

So, I'm picking a problem with the inverter or associated wiring.

[jdhurst]

The hinge runs up the length of the display and is screwed to the metal shell of the LCD itself. The lid is screwed to the hinge and other points. The hinge is totally exposed.

I get 25 Volts to free air with a very high impedance AC meter and 5 volts to earth ground. I also have run these tests multiple times over time because this subject keeps coming up (search).

So either the machine is defective, giving you shocks, and should be serviced well prior to immediately, otherwise, with a good machine, you should not get any harmful shocks.
... JDH

[Tim M]

Can you explain more about this lack of "galvanic" isolation as my impression of the charger design was different. My understanding was that the unit was double-insulated to prevent direct passage of AC.

Laptop chargers use the switch mode power supply design and are galvanically isolated. The internal transformer operates using pulsed high voltage DC, rather than converting the supply AC directly. (This is why they can use a wide range of supply voltages - typically 90-250VAC).

So, I'm picking a problem with the inverter or associated wiring.

Thanks for this. I wasn't sure what was meant by "impulse charger" but am familiar with switching power supplies. As you suggest, I don't see an AC adapter fault as a likely culprit due to the absence of other problems with the computer. If the original poster would do the test I suggested (see if the shock disappears when the LCD cutoff switch is pressed), a positive result would be diagnostic for an inverter issue.

[sb102]

I wasn't sure what was meant by "impulse charger" but am familiar with switching power supplies.

Sorry about that mistake. I simply translated the polish name into english, my bad. Also I found that the SPS can be insulated galvanicaly by optic insulators, so my bad again (I need to bite my teeth into the problem and simply build one myself). Now back to the problem: JDH's post inspired me to do a test. I dug up my digital multimeter and set it to 20 volts AC. Next I connected one of the electrodes to the metal hinge of my T40 running on AC power suply and touched the top LCD cover in different places with the other one. I got about 2.0 volts on average (the biggest potential was on the very top of the LCD cover - 2.2 volts). Next I unplugged the AC adaptor and repeated the same test running it on the battery pack. I got an average of about 0.5 volts. Next I plugged the AC PS back in and closed the lid (as Tim H suggested) - i got the same results as with the first test. Finally, I touched to the second electrode to my thumb - the result was 20 volts (on the bateries I got a steady 3.3) It is clear that the presence of a AC adaptor somehow inflicts the grounding of the notebook. This also can be the inverter. The only way to find out is to run the notebook with the battery pack in.

[jgiam]

Hi all, thanks for all the replies

sb102, yes, that's what I used. We call it a "test pen" here, or at least, my father does.

I only notice the shocks when I'm plugged into AC. Then again, I don't normally touch the edges of the screen when I'm running on battery power.

Anyway, I've gotten back the laptop for a day and so far, no shocks. Hope it stays that way.