The flickering seemed to be worst when there was keyboard or mouse activity so we initially thought that maybe the wireless keyboard and mouse were causing interference with the new monitor. We switched to a wired keyboard and mouse but still had the same problem.

We then swapped monitors with another PC but the problem stayed with the Acer laptop so the screen itself was fine. The laptop’s internal screen was fine but the external monitor was still flickering. We then spent several hours download and installing all the latest drivers on the laptop. W even updated the BIOS but still the screen flickered.

Different screen resolutions and refresh rates made little difference. The flickering varied but was always there. Then we had a breakthrough! – we noticed that when we disconnected the laptop’s power supply the flickering stopped. Faulty power supply we decided, having another power supply nearby we switched power supplies but still the flickering was there. So we tried another laptop with the Acer Aspire 5535′s power supply (the other laptop was also an Acer and the output of the two power supplies matched exactly!!) and had no flickering at all so the problem wasn’t the power supply but the laptop itself.

So we have a laptop which runs perfectly on its own but when attached to an external monitor and only when running on mains power the external monitor flickers.

Then whilst talking to a friend with an electronics background he suggested that the cause could be a ground loop between the laptop and the monitor. So I opened up the monitor’s 3 pin plug and disconnected the earth wire (as the monitor costs less and is easier to replace than the laptop!) and voila! the flickering was cured.

So it seems that the cause may be a badly designed power circuit in the laptop. I don’t know if there’s any kind of filtered sockets or plugs that would prevent a ground loop occurring and the fix I’ve used should be used with caution (seek professional advice if you’re at all unsure!) but it works for us.

It was only when I removed the old motherboard that I noticed some of the capacitors around the processor had burst slightly leaving a ‘rusty’ residue on the top of the capacitors so a few weeks later when another PC was having similar problems I took a close look and found the same blown capacitors there. Replacing the motherboard fixed it.

I’ve now had around 10 PCs with the same problem – all of them were around the same age (around 3 – 5 years) but had different motherboards so I suspect a bad batch of capacitors were around at the time of manufacture.

So if you get a PC that just does what it likes when it likes and can’t figure it out shine a torch on the motherboard and particularly the capacitors around the processor – healthy ones should be shiny and silver (unless covered in dust), if there’s any sign of bulging and a brown risidue of leaked electrolyte then consider it unreliable or likely to become unreliable!