Quick one about touchpads and EM interference

I bought another laptop recently (used, but still awesome Dell E6320) and I noticed a very interesting behaviour  😉

When I got it, I ran the comprehensive diagnostics suite embedded in its EFI firmware and it went all OK, no errors whatsoever, battery was fine (86% of its designed capacity), touchpad and keyboard worked fine as well.

As I did with all my PC, I wiped the preloaded Windows 7 and installed Arch Linux. Then it was time for copying the data from the old netbook to the new Dell laptop 🙂

I used a standard ethernet cable to connect my PCs  together. Upon connecting the cable – touchpad on Dell just stopped working, or worked only intermittently (very jumpy, completely unusable). Strange, indeed. At first, I thought it was a configuration problem to be resolved later. I went on using trackpoint and continued migrating my data and installing additional software…

Few days later, I tried to investigate this touchpad problem, There were no data in system logs that suggested hardware problem, IRQ conflict, or any other faults at all. But, still, the touchpad seemed jumpy from time to time, even when the two laptops were not connected. I fiddled with some noise reduction settings using synclient and the situation sometimes improved, sometimes didn’t change at all. I thought that it was a problem with the touchpad driver. I decided to leave it as it was, and fix it later.

Some time later, while I was working at the desk, I accidentally moved the PSU of the netbook (which was  connected to mains) much closer to the Dell laptop, and guess what – touchpad stopped working, being extremely jumpy. That was it!  The  interference from this PSU was so big, that it was making my Dell touchpad unusable!

Unfortunately, the original PSU that I had with that netbook, died, so I got a cheap, no-name replacement one. Since these PSU’s are switch-mode ones, they tend to be very noisy. These PSU’s are usually built well enough, so there’s no problem with them. The electronics is put inside a metal shielding case, and the direct current power cables have ferrite beads placed close to the plug to suppress the noise coming from the board or through the cable.

It seems that the company that made this netbook PSU has skimped on the EMI suppression, big time! ;).
So, here’s the tip for you – use high quality, good brand PSU’s – not the crappy no names!


2 thoughts on “Quick one about touchpads and EM interference

  • 8th October 2014 at 07:55

    It is quite common for touchpads in Dell notebooks. We use them often in industrial environment and it happens from time to time. Especially when a drive or inverter is close. It looks like models from the higher end (like M6500 which I use now) are much less sensitive.

    • 9th October 2014 at 17:35

      Thanks for the info! Perhaps it is somewhat vendor specific. All my laptops have either Synaptics or Elantech touchpad device, but Dell have an Alps one.


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