Member Avatar for group256

Hi everyone,

I have a Dell Inspiron 1520 laptop and everything is fine with it except that, as soon as I plug in an external monitor to it, some horizontal lines keep moving around. If I unplug my adapter and let it run on Battery, the lines disappear. I really have no idea how to fix this problem.

Any help would be appreciated.

Thanks

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  • Latest Post Latest Post by henduo12

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already demonstrated the key diagnostic pattern: the artifact appears only when the laptop is on mains power. That strongly suggests mains-related interference (EMI/common-mode noise or a ground-loop) rather than a pure driver/display problem. was correct that monitor setup can affect symptoms, and ’s question about the adapter age is relevant because filtering degrades over time.

The technical bit: modern laptop chargers are switching supplies. If their input/output filtering or grounding is poor (worn capacitors, loose windings, failing EMI suppression), switching noise and mains-frequency currents can couple into the video path. When an external monitor is connected you create another ground reference and a path for that noise, so horizontal bands or moving lines appear. Running on battery removes the mains coupling, so the lines stop.

Practical steps to isolate and fix the issue:

  • Test with a known-good OEM adapter (if not already) to confirm the adapter is the cause.
  • Plug laptop and monitor into the same grounded outlet or the same power strip to minimize ground potential differences.
  • Use a three-prong grounded adapter or a different power cord if available; avoid ungrounded 2-prong setups when the monitor is earthed.
  • Add snap-on ferrite chokes to the adapter cable and to the video cable ends to reduce high-frequency noise.
  • Try a different video cable or a digital connection (HDMI/DVI) if possible; analog VGA is most susceptible.
  • Replace a noisy/whining adapter—do not open it; return or buy a genuine OEM unit if under warranty.

Safety note: do not attempt to repair the SMPS yourself. If the adapter is physically noisy, hot, or damaged, replace it.

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Member Avatar for mechbas

I have to assume that the problem is on the external monitor. Your monitor may require special drivers with special settings that are going to be quite different than what is probably a lcd monitor on your laptop. Also, you'll have to tell the OS that you're using more than one monitor, etc.

Member Avatar for group256

errr.... Actually I have figured what the problem was, but why or how it happens, I have no idea. The problem is with my laptop charger, but when I used my friend's Dell charger, with same spec as mine, it was working fine. Mine seems to cause some noise and those lines.

Member Avatar for henduo12

Is your adapter new?

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