I just bought a Raspberry Pi 3, bundled with the stock power adapter.

When I use this power supply, the computer monitor I've connected to the Pi through HDMI is constantly turning on and off in a irregular pattern with a few seconds interval. Otherwise the Pi seems to be working properly, and I don't see the voltage warning.

When I instead power the Pi by a USB 3 port, the monitor behaves just fine.

The monitor is a DELL U2412M at 1920x1200@60Hz.

What could be the problem?

Image from Amazon

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    The monitor needs a higher voltage or more amps than the power supply can generate, or the power supply is faulty, or a raft of other possibilities depending on your set up. I'm not sure this is a Raspberry Pi issue as defined in the help centre. – joan Oct 29 '17 at 9:08
  • @joan But why would the monitor care about the power supply to the Pi? And the power supply is a official Raspberry power supply, wouldn't that make this well within the scope? It's about Raspberry hardware? – Alex - Stop it SE Oct 29 '17 at 9:13
  • if you are saying the Pi is not powering the monitor you need to clarify your question. Re question being off topic or not, that's just my opinion which differs from your opinion. – joan Oct 29 '17 at 9:17
  • @joan Thank you for letting me understand that I have to clarify the question, it's done. – Alex - Stop it SE Oct 29 '17 at 9:26
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    What monitor are you connecting to ? What screen resolution are you using ? Is it a good quality hdmi cable ? – CoderMike Oct 29 '17 at 15:38

This seems to be an HDMI hardware problem so I would approach is as an IT issue, and there are few things to persue. Power supply is red herring (IMO until any further facts are given)

Easy Things To Check:

  • HDMI Cable (replace)
  • Resolution/Refresh Mode
  • Different Raspberry PI
  • Different Display
  • Update all drivers

Cabling in particular can be a big pain to diagnose. I was once sent to a customer site to diagnose a serious issue with our product, turns out their communication cable had a broken shield wire that only caused issues when multiple things were drawing power from the same power supply, go figure.

Sometimes unscrupulous cable vendors do not perfectly meet the specification.

Sometimes old monitors with worn out input buffers have hiccups. Sometimes damaged output drivers have hiccups. So its worth trying a different monitor or different raspberry pi (or other computer).

It may be that the output mode is right on the edge of what the monitor supports but wont' complain and just try its best to synchronize. So try different output modes and update drivers.

There are many options, but the power supply would be last on the list, you have a basic HDMI Hardware Problem you need to diagnose so keep swapping things until you find the part that is broken or incompatible.

  • I got a new HDMI-cable, problem solved. Odd, I don't understand how a presumably better power supply would cause HDMI cable to fail while it's fine on a weaker power supply. – Alex - Stop it SE Nov 5 '17 at 10:22
  • @Alex Many things are possible. Cable wise internally broken wires to out of spec cable. You are mixing isolated power supplies so there are likely secondary causes involving that, to explain the inconsistent behavior. It's not a trivial Failure Analysis (FA). – crasic Nov 5 '17 at 18:33

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