T40 Shocking my Leg

[Geoff_AZ]

I have a T40, still under warranty, that shocks my legs if I'm wearing shorts. The shock feels like a pin-prick and occurs around the back of the unit--maybe where the metal screws are?--I think on both sides. At first I thought it was my leg hairs getting caught and pulled by something, but now I'm fairly sure it's a shock.

Has anyone else experienced this? Any solutions?

[christopher_wolf]

First off, are you sure it isn't static electricity?

[jdhurst]

The metal screws often go into nuts buried in plastics (not always). In any event, this crops up here on occasion, and I always have the same advice. You cannot get an electric shock from a properly operating ThinkPad (and probably other portables). There are CSA and UL laws to preclude that. So it is either static (as noted) or a defective machine. If the latter, I would head out yesterday to get it fixed. ... JD Hurst

[Geoff_AZ]

I can't imagine it's static. Too consistent and too sharp.

I hate to think about losing my T40 for some time to the shop, bit I'll give IBM a call on this.

Thanks for the input.

[rkawakami]

What is the rest of your body doing while your are operating the laptop? In other words, are you sitting on a metal chair, laying on the couch, etc.? And also, is the laptop plugged into an AC adapter? If yes, try battery only and see what happens. If you don't get any shocks from operating with just the battery, then I would suspect a ground loop and/or a mis-wired electrical outlet to be the problem.

Hhmm... I just measured the AC voltage from the I/O panel of a T21 plugged into the 72W AC adapter and the 110VAC ground pin and saw 50 volts! Yet my outlet tester says that it's properly grounded. I'm also measuring ~20uA of current. Same goes for the AC/DC combo adapter. Using a 54W power supply and the voltage and current is near zero. Why? Because the 54W supply has a 3-pin plug (with ground) and the 72W supplies only have a 2-pin non-polarized plug. That's something to be said for those "weaker" supplies.

P.S. Just to clarify what I mean by I/O panel... I connected my voltmeter from the screws holding the serial and parallel port jacks. Actually, ANY metal on the back panel is at the same potential on my T21. I would assume the same for most other Thinkpads.

P.P.S. Repeated the same measurements using a 600X. Same results. The 72W supply reads about 50VAC, no matter which way it's plugged in (remember, non-polarized plug can be inserted two ways). The 54W supply (with the grounding pin) was 0V. Ergo, if you have to operate the laptop while plugged AND wearing shorts, make sure your body is NOT grounded.

[jdhurst]

I posted the following in another forum. I thought I would post it here for all to see. My setup is not a Lab, but has reasonably precise and sensitive equipment.

I am in my Workshop, where I know (conclusively) that my outlets are properly grounded.

The voltage coming from the metal parts of my T41 very roughly a sine wave with a heavy dose of harmonics.

Device: Tek 7104 with a low frequency, highly sensitive 7A15 amplifier. P6105 10 Megohm Probe. Waveform frequency: 60 Hz. Waveform voltage: 150 Volts peak-to-peak.

Device: B&K 5360 DVM with 10 Megohm input: Voltage: 50 volts or so RMS. That is the same as the voltage above.

Device: Fluke 8022A DVM with 1 Megohm input: Voltage: 12 Volts RMS. This does not load or alter the Oscilloscope reading.

Now, Leave the Fluke to measure Voltage, and use the B&K to measure current. Connect the B&K from ground through a 1.5Megohm resistor to the Laptop metal parts. Current reading 0.00 on the 500mA AC range (lowest AC current range available). Scope voltage drops to 100 Volts peak-to-peak. Fluke voltage drops to 6 Volts AC

Now, Hookup the B&K to measure Voltage, and use the Fluke to measure current. B&K reads 45 Volts (not sure why the voltage drops 5 Volts). Hook up the Fluke as above. B&K drops to 27 Volts RMS, Scope drops to 100 Volts peak-to-peak (that looks about right). Fluke reads 9 uA on the 2mA AC current range scale.

Now, change the 1.5Megohm resistor for a 10Kohm resistor. Scope voltage drops to about 1 Volt peak-to-peak. B&K Voltage reads 0.3 Volts AC. Fluke Current reads 10uA.

Reverse the power brick in the AC outlet. No change. So I conclude there is very, very little danger on a properly wired outlet (grounding doesn't matter on a 2 wire AC system) and a properly operating ThinkPad.
... JD Hurst