emilio-movi
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Joined: Tue May 08, 2018 1:47 pm

PI3B+ not work when powered by GPIO pins

Tue May 08, 2018 2:01 pm

We have a new board PI 3B+. It works fine when it is standalone, powered by USB power supply. We try to power on by GPIO pin n. 2, 4 (+5V) and GND on pins 6, 9, 14, 20, 25, 30, 34, 39. In this case the board not work. It turn on its red LED POWER OK, but the green LED ACT is always turned off.

Important note: before the new PI 3B+ we have used without problems the same method with the PI 3B.

Could help us? Thanks.

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Burngate
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Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK
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Re: PI3B+ not work when powered by GPIO pins

Tue May 08, 2018 5:19 pm

Nothing regarding the GPIO header has changed between 3B and 3B+, so what worked on the 3B should also work on the 3B+.
And the red LED is on, so power is ok.

Have you updated the SD card before putting it in the 3B+? I assume so, since you say it works if power is applied through the USB port.

Is there a reason you have connected to both +5v pins, and all the GND pins, or am I misreading your post? One of each should be good enough.

What are you using for power supply in each case?

emilio-movi
Posts: 2
Joined: Tue May 08, 2018 1:47 pm

Re: PI3B+ not work when powered by GPIO pins

Wed May 09, 2018 7:16 am

We made more tests, and we discovered that the problem is not really the +5V but in some manner is the +3.3V

In few words, we have develooped an expansion board for interface digital inputs to Raspberry by photocoupler; there is a power supply on the expansion board providing +5V to itself and to Raspberry through GPIO pins. The board receive the +3.3V generated by Raspberry on GPIO pin 1 and 17. This voltage is required by the transistors of photocouplers.

We confirm that this configuration prevents the PI3B+ to boot: the red power LED is fixed to on, but nothing on HDMI display, etc. When we disconnect the 3.3V (GPIO pin 1 and 17) the PI3B+ boots.

We confirm that the same expansion board with this configuration with PI3B does not suffer of this problem. Probably the PI3B+ is more sensible.

At this point we think to add another regulator on expansion board to provide the required +3.3V

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joan
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Location: UK

Re: PI3B+ not work when powered by GPIO pins

Wed May 09, 2018 7:37 am

The Pi3B+ should be able to supply half an amp or so on the 3V3 rail. That should be more than enough. How much do you need and what amps can your 5V power supply generate?

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Burngate
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Location: Berkshire UK
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Re: PI3B+ not work when powered by GPIO pins

Wed May 09, 2018 9:24 am

Just a thought ...
... There are a few differences between the 3B and 3B+, which shouldn't affect most users but may catch some out.

Having enlightened us as to what you're attaching to your Pi, as well as using the GPIO header are you also using the 2-pin RUN header?
Because, on the 3B the two pins are RUN & GND; on the 3B+ they're Global Enable (on the dc-dc chip) and RUN

Bruce_Pi
Posts: 17
Joined: Tue Feb 21, 2017 5:09 pm

Re: PI3B+ not work when powered by GPIO pins

Mon Jun 04, 2018 2:22 pm

i had the same issue with pi 3b+ 3.3v.
viewtopic.php?f=44&t=214713
the pi 3B+ 3.3V regulator has some issues. I was testing an i2c shield with it and pi wont boot up.
I have used ths i2c shield with all other pi models without any issue.

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