Monitor on standby affects electric clock !

  greybeard 11:49 25 Jun 2008

At first I thought the house was haunted, but I'd be very grateful for help analysing the following problem.

First, about 6 weeks ago, we went on an economy drive after the last electricity bill. Using a plug in metered socket, I discovered the workshop monitor/pc which I thought switched off when I hit the off button, was still drawing about 0.3 amps, 24/7. So I switched it off at the mains as well.
Then we noticed the electric blanket(the bedroom sockets are through the wall to the workroom sockets) didn't work properly, after 8 months with no problems. Most of the time the neon(?) dial illuminatorwas flickering, and the blanket might or might not get warm. Appeared to be random.
So that went back to the supplier and exchanged for a new one.
That seemed ok for about 4 days, then stopped working. The power neon was on, but no heat developed.
It has an elctronic timer/controller.

Then we noticed the clock/radio in the bedroom was playing up, with either the dro flickering or the clock minute indicater cylcing every 5 seconds.

Haunted house?

I've tracked it down so far to the fact that if the monitor is switched on at the socket and on standby, the clock/radio and the electric blanket work normally. The same is true wherever the clock is taken to in the house. Nothing else plugged into the socket has the same effect as the monitor.
I've tried surge protected strip sockets as well, but nothing alters the effect of the monitor.

Any ideas ?

It would be some help if I new what type of load the monitor is presenting when on standby.


  wiz-king 13:30 25 Jun 2008

15" monitor, CRT type takes ~ 1mA when on standby ~ 150 mA when in use
I would suggest that you check all your mains plugs with a test plug like this click here any failures call a sparks.

  ronalddonald 13:42 25 Jun 2008

an electrician to check the wiring, it could be that it hasn't been checked, unless yuor an experienced electrician.

It could that the house needs rewiring, you never until you get it checked properly.

  greybeard 15:09 25 Jun 2008

I don't know why my last posting hasn't appeared, so I'll try again.
I do have some experience with house wiring electrics, as well as various branches of electronics, so I understand the points you're both making, but I would strongly suspect that there is no problem with the house wiring.

What I have been doing today is 1. I took the clock to the furthest socket, 50 yds to the bottom of the garden - no change.
2. All the wall sockets(switched) are on the same ring, but not the cooker, and that has a separate socket, so I plugged in there - still no change.

3. I ran a cable from the monitor power plug to another socket on the lower floor, but again, no change, nor then taking the clock to an outhouse socket.

It seems that wherever the clock is plugged in, it can detect the fact that the monitor is also plugged in !
Action at a distance ??

I do have a 'scope, and yesterday fired it up and got the usual mains pick-up on the probe lead.
However, if I got hold of the end of the probe wire, I could see a lot of RF on top.
Now this may be normal, with me acting as an aerial for the nearest transmitter.
I'm a bit out of my depth here, not being a radio man, but I did wonder if a fault in the clock/radio is producing some RF which is upsetting the clock electronics, as well as the blanket's electronic controller, but by plugging in the monitor I'm adding a sink for the RF.
This is getting close to mumbo jumbo, but it may spark an idea in someone.

  greybeard 15:17 25 Jun 2008

A different monitor plugged into yet another socket also produces the same sypmtoms in the clock.
Both the monitors are 22", by the way, which might explain the high standby currents.

  wiz-king 15:57 25 Jun 2008

Is your monitor a CRT or is it LCD/LED? If the later then the power block will almost certainly be a switched mode type well known for causeing RF interferance.
Also if your clock has a plasma tube display then that may have an inverter to run it, they can also cause interferance.
Also the monitor may be the only thing with an earth lead that connects to the socket and it may also have suppression capacitors across the mains and to earth. Your clock and electric blanket may be double insulated and only use two wires and not three.

  greybeard 16:34 25 Jun 2008

wiz-king - good points about the earthing.
Monitor is crt, and I think the clock is 7-segment led, but may be wrong.
I've just taken the clock next door, and it can still detect if the crt is plugged in or not !
I think that might be too far for the rf idea, and there's none on the other fm radio.
I've talked with the blanet suppliers and they have no idea, but that may not be much evidence of the possibilities !

  wiz-king 16:50 25 Jun 2008

If you have a UPS stick the clock into it and remove the mains lead, that will tell you if it is mains interference coming up the mains. With most things these days being double insulated there are not many things in the home that use the earth lead so you could have a earth leakage or high resistance / broken earth and not know it. Hence my suggestion to do an test with a test plug - an electrician will have a low ohm meter that can measure down to 0.1 ohms to check the earth properly.

  greybeard 17:07 25 Jun 2008

The clock only operates when the mains supply is connected. It doesn't at present have a battery back up installed.

  wiz-king 17:26 25 Jun 2008

UPS is a large battery backup supply for running comuters etc when the mains fails, they will supply 240V at 3 amps for about 20 minutes click here some people have the for their computers.

  greybeard 17:46 25 Jun 2008

It now is working normally.
I took it 200yards across to the farm workshop, and the symptoms were present there.
I came back and plugged into the house wiring and the glitch has disappeared.
So now I am left, baffled and waiting for the other boot to drop.

Thanks wiz-king, this may be resolved or not. I'll give it a couple of days !

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