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I'm using a Pi Zero W, testing on many power sources. I've testing all power sources with a multimeter and have confirmed that they are all 5V (+/- 0.1) and have adequate current available. 2 amps or more.

When I connect to a "bad" power source, HDMI screens get either flickering or no signal. Connected to a "good" power source they work as expected. With all power sources I'm able to SSH into the pi and do whatever I want.

Power sources that work: Wall wart, USB

Power sources that don't work: Anker power bank, Flepow power bank, 6x AA batteries in series with buck transformer down to 5V, 8x AA batteries in series with same setup.

I've found zero helpful info online and I'm stumped. My first guess was a bad power supply so I dug out a ton of batteries to test both name brand and import.

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  • if you can obtain the use of an oscilloscope, then use it to check the power supply output ...... you will probably find that the non-working supplies are very noisy
    – jsotola
    Feb 17, 2019 at 3:29
  • Power banks generally do not provide a consistent voltage. Notice they are sold for recharging other batteries not for powering electronic devices. When a device is making rapid fluctuations in current draw, the circuitry in the power bank is more likely to be biased toward flattening the current, which varies the voltage. This is a good choice if the purpose is charging. It is bad if the purpose is "power my active hardware".
    – goldilocks ♦
    Feb 17, 2019 at 7:35
  • Thanks for that info. I never really thought about the purpose of a power bank like that before, but that makes sense.
    – Jay Speidell
    Feb 18, 2019 at 3:48
  • Does this answer your question? New RPi Zero W - Screen flickers
    – Dmitry Grigoryev
    Jan 9, 2020 at 8:27

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It appears to have been a bad wire. I haven't figured out why HDMI output was sensitive to this and nothing else, but this was my solution. If I can figure out more I will update this.

Update from comment:
The bad wire I have found on the breadboard. I have LEDs and a spot to test my multimeter on, but there's one connection where the "bad" power supplies came in vs a "good" one. It could power the pi, but after rearranging wires on the breadboard and swapping a few out it worked. I believe it was a wire connecting a row on the breadboard to the 5V+ rail on the breadboard, but I can't say 100% for certain. I don't have access to an oscilloscope, so my understanding of the situation is limited. Now I have 6x AA batteries powering several devices with no issues, and all power sources work.

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  • a bad wire - where?
    – Jaromanda X
    Feb 17, 2019 at 5:00
  • On the breadboard. I have LEDs and a spot to test my multimeter on, but there's one connection where the "bad" power supplies came in vs a "good" one. It could power the pi, but after rearranging wires on the breadboard and swapping a few out it worked. I believe it was a wire connecting a row on the breadboard to the 5V+ rail on the breadboard, but I can't say 100% for certain. I don't have access to an oscilloscope, so my understanding of the situation is limited. Now I have 6x AA batteries powering several devices with no issues, and all power sources work.
    – Jay Speidell
    Feb 17, 2019 at 22:25
  • Please accept your own answer with a click on the tick on its left side. Only this will finish the question and it will not pop up again year for year.
    – Ingo
    Jan 10, 2020 at 9:45

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