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External Monitor flickering on AC power

Posted on 2008-06-19
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Last Modified: 2013-11-17
Using the AC adaptor that came with my Sony Vaio laptop, my external monitor flickers. On battery power it's fine. I've tested the monitor with other PCs and it is fine. I've tried varying the resolution / refresh rate with no success.

The AC adaptor outputs at 6.2A, using the adaptor from a different Vaio laptop that outputs at 4.7A the problem goes away, however I am worried about the potential consequences of doing this.

Anyone any ideas how I could resolve this without having to buy a new adaptor?
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Question by:NazoUK
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by:asidu
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What is the indicated output voltage of the two AC adaptors ?
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by:NazoUK
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Both identical at 19.5V
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by:burrcm
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Don't use an underrated unit. The correct one appears to be faulty (AC leakage). I would replace it.

Chris B
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by:NazoUK
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I don't believe the adaptor is faulty as I've tried an identical one from another laptop with the same results. The other laptop also exhibits the same behaviour.
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by:burrcm
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<<I've tested the monitor with other PCs and it is fine>> <<The other laptop also exhibits the same behaviour>>. One of these statements is incorrect. Have you tried a different external monitor on your laptop?

Chris B
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by:NazoUK
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Neither of those statements is incorrect; I've tested the monitor on other (non-laptop) PCs and it works fine. Testing another Sony laptop that uses the same AC adaptor produces the same results.

I've tried several monitors with the laptop all have the same flickering.
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by:asidu
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Since both xformes have the same output voltatge, both can be used. Having an overrated transformer is not an issue. If you use an under rated transformer it could be in an issue after some time.

Is it possible to measure the output voltage of the two xformers ?

Since you say your external monitors is OK and the same  problem persists on other system,  i reckon its a problem which need help from Sony.
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After a few exchanged emails with Sony and some more investigation it seems the problem I'm experiencing is called 'ground loop interference'. I've found plenty of other users experiencing similar problems on a variety of makes of laptop but no solid answers how to fix it. I've found that plugging the monitor and laptop into different outlets seems to improve but not entirely eliminate the problem.
I think I'll just risk running it on a lower rated transformer unless anyone has any insight into the problem.
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by:sdamon7
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This turned out to be true, when the power supply was removed from the laptop the external monitor went away.

We solved this by swicthing an old VGA cable with a new VGA cable that had larger Echo Supporesion nobes on the ends of the cable.

The thinking is the larger echos suppresion features on the newer VGA cable supporest the EMF that was being passed onto the extrnal monitor.
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by:sdamon7
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IN ENGLISH THIS TIME!  ;)

This turned out to be true, when the power supply was removed from the laptop, the flicker from the external monitor went away.

We solved this by switching an old VGA cable with a new VGA cable that had larger Echo Suppression knobs on the ends of the cable.

The thinking is the larger echo suppression features on the newer VGA cable suppressed the EMF that was being passed onto the external monitor.

It worked!

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