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BogoMax
Posts: 40
Joined: Mon Apr 16, 2018 4:52 pm
Location: Ireland

Pulsing LEDs (with power turned off)

Sat Sep 07, 2019 9:04 am

I bought a six socket power extension yesterday to accomodate my growing collection of computers.
I noticed after powering off and disconnecting mains power that the red and green LEDs on the Pi and the blue LED on the Pimoroni shim pulsed briefly with an interval of around 45 seconds. This behaviour continued for some time.
The power strip has two built-in USB charging ports which seem to be responsible for this.
Has anyone else noticed this and - the reason for the post - is it likely to be doing any harm to the Pi in the long run especially when the power strip is fully powered.
Did I mention that I love my Raspberry Pi(s) :D. Amazing power from a tiny device.

hippy
Posts: 6859
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Pulsing LEDs (with power turned off)

Sat Sep 07, 2019 12:04 pm

Flashing LED's would indicate power is being supplied to the Pi for at least some time. This would be like powering it up then pulling the power which could potentially corrupt SD Cards.

Kendek
Posts: 145
Joined: Thu Jul 25, 2019 4:39 pm
Location: Kaposvár, Hungary

Re: Pulsing LEDs (with power turned off)

Sat Sep 07, 2019 12:24 pm

Yes, there is something similar:

https://www.raspberrypi.org/forums/view ... 8&t=250227

If the HDMI and the USB power cable are connected, then the power LED is blinks every half or a minutes when the toggle power switch is off. Maybe a capacitor charges and then discharges in the PSU. I don't know exactly. It seems that not all PSU are affected, but the official one is definitely.

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BogoMax
Posts: 40
Joined: Mon Apr 16, 2018 4:52 pm
Location: Ireland

Re: Pulsing LEDs (with power turned off)

Sun Sep 08, 2019 5:18 pm

After changing the power strip to one in which sockets are individually switched (without any USB charging points) the behaviour was repeated so I have wrongly blamed the original power strip and its USB ports.
I've seen this behaviour before when I attempted to fit an led strip to illuminate the tuning dial on a Sansui TU-217 tuner (1980s vintage).
The tuner has a capacitor connected across the mains power switch and the leds would pulse every minute or so.
I'm using the official RPI PSU so maybe there is a similar feature at work.
Did I mention that I love my Raspberry Pi(s) :D. Amazing power from a tiny device.

Kendek
Posts: 145
Joined: Thu Jul 25, 2019 4:39 pm
Location: Kaposvár, Hungary

Re: Pulsing LEDs (with power turned off)

Sun Sep 08, 2019 5:54 pm

BogoMax wrote:
Sun Sep 08, 2019 5:18 pm
I'm using the official RPI PSU so maybe there is a similar feature at work.
Since I replaced the official PSU to a non-official one, this problem is gone, there is no more LED blinking. So yeah, I think this is a capacitor issue in the PSU.

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