Freaky PC monitor behaviour

[paulca]

So I own a rather expensive PC monitor, an Acer Predator 34" 21:9 curved 3440x1440.

Here's the weird thing.  When I plug something into the USB port, frequently the monitor switches it's display off for a few seconds and back on.  Rather alarming you might agree.

Today when I fired up my new DSO (Owon1022i) it did it when I connected the ground probe to the 0V rail of my bread board.

Now here's the twist.  The DSO was not connected to that PC.  It was connected a laptop completely separately.  A diagram might be a bit hard to do here, but I'll have a go.

Mains <---> Monitor
|               
|               
Mains <--->  PC <---> HDMI <--> Monitor
|
|
Mains <---> Laptop <---> DSO <---> Bread board PSU 0V rail.
|
|
Mains <---> Wall wart <-9V-> Bread board PSU (0-5V)

That's quite a long way and quite a lot of power supplies for any glitch to get through.

The DSO did capture a small spike, but I didn't drill into it to work out what voltage or period it was.  Bizarrely the actual probe was not connected, it was sitting on the desk, so what exactly did the DSO capture!?

[paulca]

My own poorly-educated guess is over sensitive input protection on the Acer HDMI input.

[paulca]

The lack of responses suggests that either my poorly-educated guess is correct or you all think I'm mad.

My new Tenma PSU will cause the monitor to black out for a few seconds even when just turning the load on or off.  Not every time, but about 1 in 10 times it does it, either load on, or load off.

It seems I am not alone:
http://www.tomshardware.co.uk/forum/394609-33-monitor-randomly-black-often

There is a lot of non-sense and noise in that thread, but the ones that stand out to me are the posts about sensitivity to noisy mains.

Two questions:

1.  Can I safely probe the mains with an isolated DSO ocsilloscope (note I can run it completely isolated by using the laptop on battery)... any tips as to how not to fry myself?  This is just for curiosity really.

2.  Are there any reliable mains filters?  (The PC is connected on a 4 way plug bar with ESD/Spike protection, but the monitor is on a cheapo 4 way from PoundLand.)  Would another spike filter 4 way help, or should I invest in an actual mains filter?

[BrianHG]

Try a shielded HDMI cable.  Yes, some HDMI cables are just junk, or, they don't properly conduct the frame ground between your 2 devices.
I prefer thick shielded DVI cables myself.  Transparent ones which show you a true coaxial braided conductor.

[Psi]

it's just a bit sensitive to mains spikes.

If you have a UPS laying around try put the monitor on that.

If you're feeling a bit DIY and are safe with mains, you could try adding some extra mains filter caps to the monitor at the mains input side.

Another thing ive seen on occasion, is designs where the main IC reset line is left unconnected and relies on the 50k internal pullup. Sometimes these internal pullups are a bit out of spec and dont pull hard enough to stop random spikes coupling onto the reset line and glitching the CPU

[wraper]

Try a shielded HDMI cable.  Yes, some HDMI cables are just junk, or, they don't properly conduct the frame ground between your 2 devices.
I prefer thick shielded DVI cables myself.  Transparent ones which show you a true coaxial braided conductor.

Yep, try different HDMI cable (not some $1.5 crap from ebay). You need to be aware that many aftermarket cables are junk. At least try measuring with a multimeter if connector shells on both ends of the cable are actually connected together.

[paulca]

Try a shielded HDMI cable.  Yes, some HDMI cables are just junk, or, they don't properly conduct the frame ground between your 2 devices.
I prefer thick shielded DVI cables myself.  Transparent ones which show you a true coaxial braided conductor.

The HDMI should be fine, I got stung by PC World as the monitor did not come with one and I had (in a rush) buy one of there stupid £20 ones.  I'm assuming it's good quality as it was brand name and is very thick compared to others I have seen.

However I can swap to another cable and see if it helps.

[paulca]

If you have a UPS laying around try put the monitor on that.

If you're feeling a bit DIY and are safe with mains, you could try adding some extra mains filter caps to the monitor at the mains input side.

Thanks, but UPSs are not the kind of thing I have hanging around   They cost a fortune.

I'm "mains safe" in that I have learnt the hard way several times to respect it.  However this monitor was £995 a year ago.  I don't fancy opening it while it's under warranty for a minor annoyance, but thanks for the suggestion

[Psi]

If you have a UPS laying around try put the monitor on that.

If you're feeling a bit DIY and are safe with mains, you could try adding some extra mains filter caps to the monitor at the mains input side.

Thanks, but UPSs are not the kind of thing I have hanging around   They cost a fortune.

I'm "mains safe" in that I have learnt the hard way several times to respect it.  However this monitor was £995 a year ago.  I don't fancy opening it while it's under warranty for a minor annoyance, but thanks for the suggestion

cheap small UPS is only like $100

[wraper]

The HDMI should be fine, I got stung by PC World as the monitor did not come with one and I had (in a rush) buy one of there stupid £20 ones.

This is a major concern. Shops often sell crap cables for a lot of money. When you use cables which come with equipment, there is much lower chance to stumble on complete crap.

[paulca]

Are these things worth it or junk?
https://www.ebay.co.uk/itm/Tacima-CS947-6-Way-UK-Mains-Conditioner-Surge-Protection-Interference-Filter-2M/371276645391?epid=901255975&hash=item5671d0040f:g:aIcAAOSw8w1X98ae

I'll test the HDMI cable this week end.

UPS...  Obviously the last time I looked at a UPS it cost so much I bolted far enough away to not look at them again.  A sensible UPS at £100-£200 could be very useful.

[wraper]

Are these things worth it or junk?
https://www.ebay.co.uk/itm/Tacima-CS947-6-Way-UK-Mains-Conditioner-Surge-Protection-Interference-Filter-2M/371276645391?epid=901255975&hash=item5671d0040f:g:aIcAAOSw8w1X98ae

I'll test the HDMI cable this week end.

UPS...  Obviously the last time I looked at a UPS it cost so much I bolted far enough away to not look at them again.  A sensible UPS at £100-£200 could be very useful.

Do not bother with that. The only thing you need is that monitor and computer are powered from the same line. Preferably nearby sockets (shortest ground conection between computer and monitor).

[paulca]

Do not bother with that. The only thing you need is that monitor and computer are powered from the same line. Preferably nearby sockets (shortest ground conection between computer and monitor).

They are connected to different 4 gang bars into either side of a double socket.

I run 1 essential bus and 1 secondary.  The idea is that anything I might want to leave on when I'm out or in bed goes on the essential bus plug which stays on 24/7, the secondary I switch off when I leave or go to bed.  So PC, WiFi, HD Dock, Raspberry PI are on the essential.  Monitors, speakers, lights, gizmos and bench PSU are on the secondary.  The essential has a surge protector on it, the secondary does not.

[wraper]

Do not bother with that. The only thing you need is that monitor and computer are powered from the same line. Preferably nearby sockets (shortest ground conection between computer and monitor).

They are connected to different 4 gang bars into either side of a double socket.

I run 1 essential bus and 1 secondary.  The idea is that anything I might want to leave on when I'm out or in bed goes on the essential bus plug which stays on 24/7, the secondary I switch off when I leave or go to bed.  So PC, WiFi, HD Dock, Raspberry PI are on the essential.  Monitors, speakers, lights, gizmos and bench PSU are on the secondary.  The essential has a surge protector on it, the secondary does not.

If HDMI cable is not a complete crap, this should be the main reason of the problem. If there is no direct connection between ground wires in the sockets, then the shortest ground path among all equipment around will be through the HDMi cable.

[paulca]

If HDMI cable is not a complete crap, this should be the main reason of the problem. If there is no direct connection between ground wires in the sockets, then the shortest ground path among all equipment around will be through the HDMi cable.

Interesting.  So how does this work?  I assume by "ground" we are not talking about Earth as the only components in question that are in the circuit that have an Earth are the PC and the bench PSU which is new on the scene and the problem pre-dates it.  The monitor powers from a 180W DC power brick.  So the "spike" must be on neutral or live.  I suppose the AC/DC brick uses the neutral as the DC ground/0V?  I would also expect the brick to have mains filtering caps.

A spike on Live or Neutral would be seen by all components on the same mains circuit and would dissipate slowly over distance due to resistance/inductance in the cooper wiring.  So if the spike hits the shortest route first and there is a shorter path to the monitor through the HDMI the spike comes via the ground on that before the monitor receives the spike via the mains?  Is that how it works? 

Momentarily (picoseconds?) the PC might have a few mV higher ground plain than the monitor and the two try and equalize via the HDMI cable?

[wraper]

So the "spike" must be on neutral or live.

I was meaning earth wire in sockets. Most of electronics have Y capacitors between live wires and earth which normally is also a ground. So spikes will get into the earth easily. Even more, when you plug something into the socket, at that moment Y capacitors will charge with high current.

I suppose the AC/DC brick uses the neutral as the DC ground/0V?

Do you realize that the rest of EU outside of UK don't even have polarized mains sockets?

[madires]

Have you checked the earth/PE wiring of the wall sockets?

[paulca]

Do you realize that the rest of EU outside of UK don't even have polarized mains sockets?

For a second I read that as "non- polarized mains".  Had a bit of a Mandela effect moment, but thankfully you mean the plugs are not polarized and can be flipped.  We do have 2 pin device side plugs where are non-polarized of course.

The only thing that raises a question there is... which side do you fuse?

If I grab the neutral wire and earth I'll probably be fine, not going to test that with my hand though.  If I grab the live wire and earth I probably won't be okay for a while, I have tested this accidentally and I wasn't okay for a while, it hurt like hell and I got stuck.  Thus the Live side needs a fuse to remove the risk of the live wire causing issues.  if the plug is not polarized then fusing the neutral still leaves the live wire live and the potential of shock if it's inadvertently grounded still exists for the whole length of the cable and potentially the device itself (if it has shorted live to the metal case).  This is why in the UK things that have metal cases often have polarized device plugs with Earth like IECs.

[paulca]

Have you checked the earth/PE wiring of the wall sockets?

Nope.  I could test resistance from an Earth strap to a socket earth, but, I'm not sure I have a lead long enough.   I could test that both 4 way (chains) all have connected earths.

Besides the only thing that has a connected earth is the PC, due to the metal case in the PSU (and the bench PSU).  I'm 99% sure the monitor, laptop and every else is L/N only.

[iainwhite]

I think I would try to narrow down the issue by eliminating certain items one by one.
For example, try running your monitor on the same power strip as your PC, to eliminate the 'poundland' power strip... 
then maybe try with pc and monitor on the poundland strip?   or maybe with PC & monitor direct to wall? or a third power strip?
That way you can see what might be contributing to the issue.

[paulca]

Thanks.  I'll maybe get round to it.  It's honestly merely an annoyance rather than a real issue.  I was worried the first few times, but it comes back everytime, so I just tut at it and roll my eyes now.

I'll update the thread if I find the issue.

[paulca]

So I'm bumping this to cite another example that will consistently freak the monitor out.

Testing mains leakage on a device.  Seriously?  I powered on my FY6600 and then connected one side of my DMM to earth and touched the other probe to the FY6600 BNC.  I measured 96V AC but everytime I touched the BNC the monitor blanked.

I actually think it's getting worse, or my electronics projects are messing with my electrics more often.

Thankfully it does it spontaneously only rarely and I expect that is probably someone turning something large in the neighbour hood or apartment building.

The thing that annoys me is this is a £1000 monitor, not a cheapy.

[rsjsouza]

After I changed my work laptop to one that has a dock that has both USB hub and video, from time to time connecting a powered gizmo to one of its USB ports causes the same symptoms as your original post.

The way I suppress this is by either connecting a 3k\$\Omega\$ resistor or my DMM in LowZ between the two GNDs before plugging the cable.