Why does my monitor's on/off light flash continuously after I unplug it?

This is not a problem but I want to know what's going on with my LG L91A 19" monitor. I've been using this monitor for the last 3 years and I have no problems with it. Recently I realized something strange:

After I use my computer, I always switch off my multi-outlet electrical socket which provides electricity for my PC, external HDDs and monitor to make sure that there is no electrical flow through the system. While I was staring around the monitor, I realized by chance that the on/off light on the bottom-right corner was flashing every 15-20 seconds. It flashes in a pale blue color. Normally when the monitor is on, it is always on with a strong neon blue color. First I thought that this could be due to the capacitors, but after a few hours the flashing was continuing as I checked it. I observed this situation several times. Another thing I realized yesterday was that a few minutes later as I cut off the electricity, the monitor's screen flashed just for a split second in a semi-bright gray color. I thought that it is some kind of electrical discharging but I'm not sure. Is that normal? What's going on inside my monitor?

My multi-outlet electrical socket is something like this:

alt text

Mehper C. Palavuzlar

Posted 2010-01-27T08:35:01.250

Reputation: 51 093

Does your monitor behave the same when you completely disconnect the powercord from the socket? – Martin – 2010-01-27T12:43:57.997

Last night I disconnected just the powercord of my monitor from the multi-socket, and afterwards there was no flashing! – Mehper C. Palavuzlar – 2010-01-28T08:11:21.450

1Many monitors have a built-in USB hub, it could be drawing from that. I suppose another device on the multi-outlet strip could be backfeeding a little DC voltage to its syblings, which could be enough to light an LED. That could be verified with a multimeter. – kmarsh – 2010-01-28T13:23:13.683

@kmarsh: You're right. I unplugged the others and the monitor stopped flashing. Now it's obvious the other devices are backfeeding the monitor, but why? Is it normal? – Mehper C. Palavuzlar – 2010-01-28T15:12:23.167

Normal, yes, correct, no. Just bad design. Any battery chargers on the strip? They would be my first suspect. You can find the offender by plugging in one at a time until the monitor flashes. – kmarsh – 2010-01-29T13:06:32.540

Sometimes I plug in battery chargers, you're right. – Mehper C. Palavuzlar – 2010-01-29T14:16:44.857

Are you sure all the outlets on your power strip are switched? The monitor is probably plugged into an "always on" outlet on the power strip, and when you turn off the computer, the monitor goes into standby mode (the same thing as when you just shut off the computer). – rob – 2010-01-29T20:49:38.723

I am sure, I tried it. The monitor gives a continuous yellow light when it goes to standby. – Mehper C. Palavuzlar – 2010-01-29T21:17:49.387

Answers

Are you sure that the Monitor is still plugged to the multi socket? Sounds like the monitor is taking the energy from somewhere else because I can not think that a capacitor can maintain the led on/off [and the electronics to detect that there is no signal] for hours.

EDIT 1: Your last comment makes me think that what I said about some energy coming back from a third device is true. No need to be an UPS, just a device with big capacitors that can give energy back. Try to unplug not the monitor but the other devices to see when the monitor stops flashing and you will get the one that is giving energy to the monitor. Just try

[He says that this is what is happening and asks if it is normal]

EDIT2: Yes, its pretty normal. Devices have capacitors to do several things. [Making it simple] Capacitors store electrical energy inside. When you stop the devices the capacitor has energy inside and probably the output of the capacitor is opened due to the switching off so the capacitor releases its energy by its input. Nothing bad can happen, for sure, its a normal operation

Ignacio Soler Garcia

Posted 2010-01-27T08:35:01.250

Reputation: 1 729

I'm sure it's unplugged while off and there's no electricity. That's why I find it strange. – Mehper C. Palavuzlar – 2010-01-27T11:37:49.100

Mmm, maybe you have something more attached to the multi socket that has big capacitors and they are giving the energy to the monitor ... – Ignacio Soler Garcia – 2010-01-27T12:06:18.130

Believe me there's no UPS or something like that. – Mehper C. Palavuzlar – 2010-01-27T12:11:22.563

1Your last comment makes me think that what I said about some energy coming back from a third device is true. No need to be an UPS, just a device with big capacitors that can give energy back. Try to unplug not the monitor but the other devices to see when the monitor stops flashing and you will get the one that is giving energy to the monitor. Just try. – Ignacio Soler Garcia – 2010-01-28T09:12:33.290

@SoMoS: You're right. I unplugged the others and the monitor stopped flashing. Now it's obvious the other devices are backfeeding the monitor, but why? Is it normal? – Mehper C. Palavuzlar – 2010-01-28T15:11:28.503

1Yes, its pretty normal. Devices have capacitors to do several things. [Making it simple] Capacitors store electrical energy inside. When you stop the devices the capacitor has energy inside and probably the output of the capacitor is opened due to the switching off so the capacitor releases its energy by its input. Nothing bad can happen, for sure, its a normal operation. – Ignacio Soler Garcia – 2010-01-28T17:12:57.663

@SoMoS: If you could arrange your answer adding your latest comment to it, I'll set it as the accepted answer. Thanks for your explanations. – Mehper C. Palavuzlar – 2010-01-29T11:39:38.437

Here you have, glad to help. – Ignacio Soler Garcia – 2010-01-29T19:08:00.353

I agree that this might be an electrical discharge. Do you turn off your monitor before you cut the power? If no, please do turn it off first. I can imagine such side effects from directly cutting power...I have a TV (flat screen), which is brightly flashing and sounds like it just imploded if I directly cut the power without shutting it off first.

Bobby

Posted 2010-01-27T08:35:01.250

Reputation: 8 534

When I shut down my PC, the monitor automatically turns off itself. So I don't turn my monitor off from its button. I didn't know this is harmful... – Mehper C. Palavuzlar – 2010-01-27T11:39:51.170

@Mehper: I don't know if it is harmful, that was just my first idea and my experience. – Bobby – 2010-01-27T12:06:59.360