Power socket makes computer screen backlight go off
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scitrek
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Power socket makes computer screen backlight go off

Post by scitrek » Sun Nov 27, 2022 7:18 pm

Hi all

I'm experiencing a really weird issue with some of the power outlets in my home office. I have a surge protected power strip to which a laptop and 3 screens are connected. I've always attached the strip to a specific socket in the room with no issues.

Recently I discovered that if I plug it into a different socket (on a different wall), one of the 3 screens doesn't turn on the backlight. The screen itself is powered and works (Windows recognises it and the mouse moves to it) but the backlight simply doesn't turn on. If I plug the strip into the outlet next to the one with no issue, only part of the backlight comes on (the left and right edges don't).

I'm trying to figure out what could cause this, if it's reason to be alarmed and how to fix it. I've plugged in tone of those socket testers off Amazon (specifically this one) but all looks good, I've measured the voltage suspecting wild fluctuations but it's stable at 240/241 V. I'm going to test continuity to understand how the ring is built through the sockets, but I don't think that'll help much. What else could I check?

Mr White
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Re: Power socket makes computer screen backlight go off

Post by Mr White » Sun Nov 27, 2022 8:58 pm

I would say you are overcomplicating things, it sounds like one of your monitor/screens has a bad connection.

I would suggest you try the particular monitor in a completely different socket.

scitrek
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Re: Power socket makes computer screen backlight go off

Post by scitrek » Mon Nov 28, 2022 1:01 pm

Sorry, I might not have explained it right. The screen works fine whether connected directly or via the strip to the "good" socket, whereas the backlight turns off on the bad one (whether directly connected or via strip, even with a different cable) or it turns partially off when connected to the socket right next to the good one.

One thing I forgot to mention (might be significant) is that after the issue, even plugging the monitor into the good socket requires a reset (completely draining the power from the screen) before reconnecting, otherwise the issue persists. After resetting and reconnecting to the good socket, all is good.

Mr White
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Re: Power socket makes computer screen backlight go off

Post by Mr White » Mon Nov 28, 2022 9:32 pm

I still suggest the problem is with the monitor or its cable.

ericmark
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Re: Power socket makes computer screen backlight go off

Post by ericmark » Sat Dec 10, 2022 11:36 pm

The tester you are using does not do a loop test, so there are faults it can miss. But it does seem strange, out of interest are the sockets RCD protected?

In the main computer equipment is extra low voltage, and some where there is a switch mode power supply reducing the low voltage out of the sockets to extra low voltage, so in theory at least one would need a very large fault to cause what you report.

It seems likely due to some RF interference, be it an extension reel coiled up, or power cables close to other cables, but could be as simple as some strain on the casing opening or closing some poor connection.

scitrek
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Re: Power socket makes computer screen backlight go off

Post by scitrek » Thu Dec 22, 2022 10:28 am

Hi erikmark, thanks for your reply.

ericmark wrote:The tester you are using does not do a loop test, so there are faults it can miss.

Any way I can test for that?

ericmark wrote:But it does seem strange, out of interest are the sockets RCD protected?

They are, insofar as there's an RCD in the main switch box where the line is derived from.

ericmark wrote:It seems likely due to some RF interference, be it an extension reel coiled up, or power cables close to other cables, but could be as simple as some strain on the casing opening or closing some poor connection.

I was thinking the fault has to be in the socket or wall wiring as that's literally the only place where I'm changing things. There's a power cord going to a surge protected power strip that's firmly fixed to the table, and all devices are then plugged into this one with cable management, so the only thing "moving" is the loose end of the power strip being moved from one socket to another.

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