gbl08ma
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Screen goes black when turning things on or off

Wed Jul 23, 2014 5:22 pm

I received my first Raspberry Pi B+ last Monday. Everything works fine and I'm happy with it, except for an issue: often, when things are turned off or on, or plugged in or out of the mains at any place in the house, the screen goes black for about a second, before coming back. The Pi does not reset, it keeps operating normally: the power led keeps steady, USB devices don't turn off (and if there's any data transfer in progress, it is not affected), ethernet is not affected and any keyboard or mouse input takes effect during the time the screen is black.

My setup consists of having the Pi powered from a 1A power supply that came with a ZTE USB 3G/Wifi router (so, not a phone charger). Connected to the USB ports I have a keyboard, mouse and flash drive (from which Raspbian is running, but the problem persists when running other distros or RiscOS). There is no hub and ethernet is connected.
The connection to the monitor, a Dell E228WFP, is made through a HDMI to DVI adapter and then a 1.5 meters DVI-D cable. This same cable, adapter and monitor work fine with my laptop, without screen flickering issues.

Things I've done to mitigate the problem, without success:
- Searched the internet a lot and tried solutions for problems that are similar to mine, but not the same (I couldn't find anyone having the same problem);
- Set config_hdmi_boost to 4, and then to 5. At this point, I don't think increasing this value is going to be of any help (and I don't want to fry the DVI logic on the monitor with a too strong signal);
- Tried many different power supplies. Most ones I have say they give 1A, but I also borrowed a 2A original Samsung Note II charger - interestingly, with this one, the monitor blinking issues were even worse, with the screen going black randomly about every five seconds - and sometimes staying black for over two seconds. It was so bad I did "sudo halt" right after the RPi finished booting. I guess this is because this is a charger, possibly optimized to charge the Samsung phone and not a power supply for general use;
- Connected the ZTE power supply to an outlet without an extension cord or anything else connected;
- Connected the ZTE power supply through a UPS - this made the problem even worse, because blackouts would also happen whenever the UPS decided to switch supply to/from batteries.

The "blackouts" only happen when the Pi is connected to the Dell monitor. If I connect it to my TV set though HDMI (with a HDMI-HDMI cable), the image on the screen is steady. On the Dell monitor, to induce a blackout, it's as simple as turning on/off my desk lamp, turning on a fluorescent light anywhere in the house, turning on the toaster or having the dishwasher turn its pump on or off, to list some situations. If there's a problem with the electrical system, it hasn't had consequences in the last 20 years, and we've been powering all sorts of electronic devices without problems.

My theory for why it happens: whenever there's a fluctuation in the mains voltage due to things going on or off, the power supplies I have pass that fluctuation on to the Raspberry Pi (all the power supplies I have with a USB connector are of the switching type). The Pi doesn't have any problem with this fluctuation as it is certainly well within operating range, but it causes some noise on the HDMI output. My TV set has no problems with this noise and goes on happily, but my computer monitor freaks out and blacks the screen out, taking some time to recover (going to the point of saying there's no input signal, if the noise persists due to additional fluctuations on the mains voltage).

How I could fix it (but I would like other people's opinion before buying the things to attempt these steps): IMO the ideal solution would be some sort of filter/rectifier on the 5V output of my power supplies. I don't know if the "made for the Raspberry Pi" power adapters you see online would have enough quality to filter these fluctuations, and I don't feel like spending money to find out, so if someone knows, please tell. I think another solution would be to use a transformer-based power supply (I have read these give a cleaner output), unfortunately I don't have any around to test - and if I had it most likely wouldn't have a USB connector, meaning I'd need to do some trickery that could possibly cause more problems.

Does anyone have any suggestions to solve the problem? I can make a video if the situation is not clear enough...

Thanks in advance.
Gabriel

klricks
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Re: Screen goes black when turning things on or off

Wed Jul 23, 2014 7:57 pm

I would suspect a problem with the power supply, inverter or light tubes in the monitor not the RPi.
When the screen is dark shine a bright light directly into the screen and see if you can see the screen content.
I have fixed several monitors myself by changing capacitors.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

gbl08ma
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Re: Screen goes black when turning things on or off

Wed Jul 23, 2014 8:07 pm

It's not a problem with the monitor, as I said the same setup (HDMI->DVI+cable+monitor) works fine with my laptop and additionally, the analog (VGA) input of the monitor, which has been used for a long time, never showed this problem.
It's most definitely a problem with the power supply, but I'm kind of surprised that it doesn't affect more people... it's not a case of the power supply being bad, because I tried over five different ones all with the same results (or worse, if they didn't provide 5V but more like 4.75V when under load).
Now, I wonder if more expensive "for Raspberry Pi" adapters like this one https://www.modmypi.com/raspberry-pi-ac ... e-cable-eu would work better, I would guess not, because they are still switching power adapters and apparently don't show any difference from the ones I already have laying around.
I could use some bulky device like my laptop or desktop to "filter" the power (both have special "charging" USB ports that provide at least 1A, and thus are suitable for powering the Pi), but that would defeat the purpose of my setup a bit because then I'd need to keep a high-powered device running (or at least, physically connected) to use the low-power Raspberry Pi.

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Burngate
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Re: Screen goes black when turning things on or off

Thu Jul 24, 2014 7:23 am

gbl08ma wrote:... It's most definitely a problem with the power supply, ...
I would have to disagree.
You've tried several supplies, and it happens with them all.

Does the PWR led blink when the monitor goes off?
I assume the Pi doesn't reboot?

Pi into monitor => problem
Pi into TV => no problem

It's the monitor.

So why doesn't the VGA input to the monitor not show the problem?
Answer - are you sure it doesn't? Have you tried putting the Pi into that input, through a HDMI-VGA converter?

And why does it not happen with the laptop?
That's harder to answer. In fact I find it impossible to answer.
I had a similar situation some time ago. Laptop through VGA into monitor (it was before the Pi came out), momentary black screen whenever the boiler fired up.
Happened even using laptop's battery, no mains input.
The monitor didn't reset itself, so it wasn't (as far as I could see) the monitor's supply.
All associated earths tested fine. Same using a different wall socket. Ferrite beads on all leads made no difference.
Solved by buying a new monitor.

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RaTTuS
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Re: Screen goes black when turning things on or off

Thu Jul 24, 2014 8:22 am

I suspect the Dell...
I have 30+ of those at work
mostly they are fine
very occasionally one of them that I have an RPi plugged in via a HDMI to DVI adapter will flicker on / off
another one will not tell the RPi that is is connected via HDMI so boots to RCA output unless I force it and then it's fine.

over the last 5 years I've had 2 of those monitors develop vertical lines of colour [1 pixel wide]
1 had a square block filled with static
1 failed completely

if you have a better HDMI lead that may make things better , or use HDMI_boost option YMMV

they are very very tight on their energy usages - not over engineered at all

it's possible the monitors PSU is on it's way out.
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
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gbl08ma
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Re: Screen goes black when turning things on or off

Thu Jul 24, 2014 10:32 am

No, the power led doesn't blink when the monitor goes off, but the OSD is inaccessible during that short time (which is not strange - it can't be accessed when switching inputs nor when the monitor shows the message that's entering power saving mode). Furthermore, when the screen is black, it's not a "true black", all it does is turn all the pixels black and keep the backlight on (this is a good old LCD monitor that doesn't know better, unlike my TV and many LCD-LED screens).
I don't have a HDMI to VGA converter to test (and if I had, it could still work if the problem was on the Pi, it would only need to deal with the problem on the signal better than the monitor does).

Well, it can be the monitor - perhaps, the signal the Pi sends is weaker than that from the laptop, and thus is more susceptible to interference on the monitor's part. And the fact that it doesn't happen on VGA can be due to the VGA logic being more physically apart from the transformers inside the monitor, or being more resilient to interference (even though it should be the other way around, since DVI-D is digital and VGA is analog).

I also found the monitor freaks out easily, yesterday when I was playing with power supplies for the Pi, it decided to show all garbage (even the monitor Main Menu would show garbled) and wouldn't stop doing it until I disconnected it from the mains (the power button on the monitor wasn't enough). I think it freaked out because the DVI cable went a bit out of the connector - but that doesn't mean it shouldn't have recovered once it was properly inserted.

Just to get rid of any doubts, and so that I can safely increase the maximum USB output to 1.2A, I ordered a 5.25V 2A power supply from ModMyPi along with a apparently thick USB<->microUSB cable. Let's see how it goes. If the problem persists, I can always keep using the monitor with my desktop and laptop as before, and use the Pi connected to the TV or headless (for what it will be doing, it makes no difference).

lumsdot
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Re: Screen goes black when turning things on or off

Sun Mar 15, 2015 11:00 am

my pi2 has the same problem, almost.
if high power items are switched on in house like iron or electric heater, i get a flicker on lg monitor, it never did this with my pc, so i suspect pi or its power supply, i have a 2 amp us kindle power supply sitting in a shaver adapter i.e us to uk adapter.
guess i need some kind of power filter or a new power supply less suseseptical ( spelt wrong) to interference. im guessing a genuine apple ipad usb power supply would be better, they have very good regulated outputs according to experts

Wicked1983
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Re: Screen goes black when turning things on or off

Tue Aug 22, 2017 6:38 pm

Hello, I have the same problem. When turning on and off some lights (fluorescent bulb) there are black screen (turning light off) and a bit of flickering (like noise) on the screen (turning light on). Moreover I have a lot on instability with my raspberry. I found it after hours (no more than 24) with the main sd card disconnected and an error message saying (ATSC removed without ejecting). It also happens sometimes that filesystem is corrupted :(

pcmanbob
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Re: Screen goes black when turning things on or off

Tue Aug 22, 2017 9:34 pm

Hi.

Possible causes your power supply is under-rated or of poor quality or the cable between the power supply and the pi is of poor quality, so causing low voltage condition on the pi which would result in corrupted SD card.
to fix get better power supply like https://www.raspberrypi.org/products/ra ... er-supply/

your house wiring/mains power supply has a fault on it which results in a main voltage dip or brownout when ever a large load is switched on or off

your light fittings are putting noise out on to the mains cabling when they are switch on which is affecting all other sensitive mains power equipment in the house like you pi and screen.
to fix the second 2 get an electrician to inspect your mains electrical system.
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