Monitors turning off when one of them is unplugged

[ARW]

OK so this actually work related but it has me stumped.

The IT unit at a school has new wiring (1 year old) and on one work station bench there are about 12 or so computers and monitors all powered the same ring circuit.

Each double socket powers one computer and its associated monitor.

It has been discovered that when you unplug or plug in a monitor that sometimes some of the other monitors (either to the left or right of the monitor that is been plugged and unplugged) lose their display for a few seconds[1].

I have checked the circuit and it is fine.

Any ideas.

One other bit of info. The slower you plug or unplug the monitor seems to make this happen more often.

I can go back in for another look if anyone wants any more info. My job was only to confirm that the circuit was safe but I like a mystery.

[1] So the school closed the IT room for H&S reasons.

[Andy Burns]

Presume by "unplug" you mean the power lead, rather than the VGA/HDMI/etc lead?

Do the monitors have external power bricks, or just an IEC mains lead direct to the screen?

If they have bricks, do they do it when when brick is unplugged from the monitor, or just when the brick is unplugged from the mains? Do they do it when the monitor it powered on/off by the front panel button?

Are they no-name or branded monitors?

[Martin Brown]

Sounds like some sort of interference from sparks disrupting the signal integrity. I presume they are all on digital interfaces these days?

Does it also fail if you plug and unplug an anglepoise lamp or similar

60W load that isn't one the monitors.

I presume you have eliminated the possibility of loose wiring in the various sockets on the ring main (and/or it not being a proper ring). A better quality of interconnect between PC and monitor might fix it.

Be worth checking that there is a proper earthing arrangement too.

Why are things getting plugged and unplugged though? Less wear and tear to switch off at the wall or have a master off switch for them all.

My favourite in the days of tube based monitors when mobile phones were new and exciting was watching the screen go crazy as the phone woke up when it was about to ring and accept a call. It gave about 3s warning.

[spuorgelgoog]

I have similar problems with laptops and TVs. Turning the TV on/off or plugging/unplugging it wakes the laptop up.

Owain

[Andy Burns]

Does the laptop "know" about the TV via a WiFi or Bluetooth connection?

Could it be something simpler such as the physical act of plugging nudges the mouse which wakes up the laptop?

[Chris Bartram]

I'd say the same. We once had a set of desks here where one monitor continually flickered after we replaced the PCs. We eventually found an IEC lead on an adjacent monitor (plugged into the same PDU) had a rewireable plug (rather than a moulded one) with loose screw connections. I'd imagine if it was a higher wattage appliance it would have got hot.

[Jethro_uk]

I am imagining that somewhere buried below you might find one of those "smart" extensions which powers down when the current draw from a specific socket goes to zero. They had a brief vogue when people were mixing all sorts of kit, and just switching the PC off would also power down printer, monitor, scanner, speakers etc etc.

The fact it's a school is suggestive. Just the sort of institution to mandate such kit as part of a "green" initiative.

[Brian Gaff]

Perhaps its run from one of those sensor socket bars that detect current and then switch other sockets on. If you disturb some of those they can misbehave. Brian

[Andy Burns]

Schools in general seem quite "anti" 4-way extensions ... if it's an ICT suite they do tend to install sufficient power and data points.

[ARW]

No adaptors, just MK double sockets with one socket for the computer and the other for it's associated monitor.

[ARW]

Yes the 13A socket.

I'll try and have another look later in the week.

ISTR the monitors had bricks, and were either Dell or HP.

No one tried the on off button on the monitor.

[cpvh]

To answer an earlier response. We stopped using master switches for banks of computers in classrooms when the computers started blowing their PSUs. If you turned of 30, only 25 would come back on. After a short while the d ealers wouldn't fix em under warranty.

[Jethro_uk]

Maybe in sight, but what horrors are locked away below ???

[Jethro_uk]

Meanwhile, chez Jethro, 4-way extensions have become a standard feature.

I cannot believe the hours I have spent scrabbling around behind furniture to access a plug in a room - notwithstanding the usual plug/ appliance ratio problem.

Not sure where inspiration came from, but about 10 years ago bought a bulk of 1m 4-way extension leads. Plug into a socket in a room and - presto ! You've got access to moveable power. Since the biggest thing that is ever plugged in is the hoover, I feel we're quite safe.

Cheaper than fitting 4 more double sockets (all of which would be full now anyway). Just have a rule that we never plug another adapter into an adapter.

[Huge]

+1 (or perhaps I should say +4?)

We have dozens of them, for the same reasons you state.

[charles]

did you know you can now get 6 way, 8 way 10 way and even 12 way ones?

[Huge]

I have 3 off 12-way and 2 off 20-way ones in my study.

[Jethro_uk]

It's one of those "how on earth did I not think of it before" ideas.

Although pricing may be an issue. IIRC last time I bought "an" 4-way lead it was a pack of 3 for £10 - cheaper than the 3-way cube adapters (which I have junked).

[Rob Morley]

You must have a load of wall warts. I've not found a need for more than a few 6-way strips, I like the individually switched ones. Using

4-way USB chargers saves a few sockets.