Thinkpads Forum

I just noticed recently that, there seems to be lots of static electricity on the D-sub/VGA connector on my X61T.

Anybody has similar experience?

WOW, never heard of such a thing. How can you tell? When you touch it is there a shock, or do you see a spark? Also, did you use a digital multi-meter and check to see if there is constant voltage between the shield and whatever you are connecting it to?

Note of interest; in winter months when air is very dry (low humidity), as is the case in a typical home, the potential for static charges builds significantly. If you wear clothing with a high static potential, and/or walk on carpet with a high static potential, if that shield is well grounded, then I'm not surprised to hear of the static charge ... but it's likely a static charge coming from you!

If the only source of static charges in your home (or office) is that VGA cable then there could be a serious problem. But if you are touching other grounded metal objects and getting shocked the static charge is on you! Common this time of year (unless you live down under where it's now summer )

loyukfai:

Are you really describing a static charge on your connector? If it were static, one touch would remove the charge, so it would be a one-time event (at least until you walked across the carpet on a dry day and touched the connector again). And as sojourner has said, the static charge would be on your body; not on the PC.

Instead, are you describing an ac voltage that is on the shell of the connector? This is more likely. Do you notice a small spark when connecting an external monitor? Or, do you feel a slight tingle when touching the connector? Is this what you observe?

If so, a possible explanation is the AC line bypass capacitors from each side of the line to ground in the power adapter. The capacitor values are small enough so that they are a high impedance at the line frequency, but if you measure the voltage with a high-impedance ac DMM when the case of the adapter (and PC) are not connected to ground, you'll likely measure half of the AC mains voltage. In the US with our 120V mains, you'd typically measure 60 V. If your adapter has line bypasses and you are connecting the VGA connector to an external monitor that has its chassis grounded, then it is entirely possible that you might see a small spark when you first make the connection. If the behavior has changed recently then perhaps you have a defective adapter or a problem with the external monitor.

Thanks for the information, I'll need to look into it further. The problem is that, when I lift the computer with my hands, some of the tips of the fingers of the left hands feel being hit by needle(s). And I figured last night it's probably (but may not limit to) the D-Sub connector.

I can put my fingers on it, feel the "jolt", and it will be gone after a short moment. But once I remove the fingers for a few seconds and touch the part again, the jolt is back as well.

I may have a lead... I checked with a multimeter and found the socket's live and neutral leads are reversed, could it be the problem...?

That would be one explanation. The other would be that the AC adapter has a fault. In cases where the AC outlet does not have built-in polarization (one blade larger than the other or positioned/angled differently or has a dedicated ground terminal) and the AC cord on the adapter is also not polarized (identical blades and only has two), you can try flipping the plug over and see if that helps. Since you know that particular socket is mis-wired, I'd try another one in your house, first checking to see if it is also wired wrong.