Dell Touchpad - erractic movement

[Stephen041085]

Hi all.

 

Hope somebody can help with this one.

 

We are experiencing some random erratic movement on the touch pads of some of our Dell E5520 laptops.

 

This only occurs when the laptop is docked (Dell E-port) and thus connected to the wired network, usb, speakers and projector (Dell S500WI).

 

As the projector is interactive (with a pen which acts as a mouse) we have made sure that the pen is turned off, which makes no difference.

 

We have also updated the touch pad drivers, which again made no difference.

 

When un-docked, the laptop exhibiting the fault has no touchpad problems - put it back on the dock, and the problem returns.

 

I believe (although i need to check) that we have narrowed the problem down (by unplugging everything one by one) to being the vga cable between the laptop and the projector. However, the installation across the school was done at the same time using the same equipment, but is only affecting a handful of users. All the laptops are identical E5520's (again purchased at the same time) and have identical software images on them.

 

Has anyone come across this before or have any ideas on what to look for next?

 

Thanks,

Stephen

[agentz]

This is probably a long shot, but we had something similar with our set ups in our primaries... about 18 months ago we rolled out a batch of Dell E5510's without any issues. We then replaced a bundle of projectors with NEC NP310Gs and a number of users started reporting 'jittery' cursor movement, and jaggy horizontal lines when drawing on their Smartboards. Like you I eventually narrowed it down to only happening when the VGA cable was attached.

 

Turns out that the previous projectors had been grounded, the NECs were double insulated, and the E-port replicators we'd just put in were also DI (they shipped to us with the two-pin version of the mains jack, randomly the next batch had three-pin sockets on the mains input side). Some weird ground loop interference I guess. Was able to prove it to one of our sparkies who was very sceptical about it by using an anti-static wrist strap (the sort that clips on to a yellow plug) and croc-clipping it to one of the thumscrews on the VGA connector.

 

Eventually convinced our property maintenance people to re-wire VGA sockets to ground them properly for any users experiencing the issue.