rhubarbdog
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5 volt GPIO power pins broken

Wed Aug 22, 2018 1:26 am

I was trying to remove a HAT which had become bonded to my raspberry pi and slipped a bit. The pi stopped working, so i bought a new one. When it arrived I swapped the disk over to find i'd damaged the disk. I had a new NOOBS in pi zero I was still setting up. I tried the new disk in the 'broken' pi it booted so i kept the new one in the box.
The problem is the 'broken' pi is not 100%, i'm still researching the damage but there is no power to the 5 volt GPIO pins, USB devices are working. I've not checked my USB voltage I have a 'USB power lead' which is cut in half, but i couldn't find it.

Is it easy to get the 5 volt back to the GPIO i can solder a bit and would be happy to add some extra wires to the 'broken' pi, it owes me nothing.

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Imperf3kt
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Re: 5 volt GPIO power pins broken

Wed Aug 22, 2018 1:55 am

How are you determining pins 2 and 4 have no voltage?
Technically speaking, they connect (almost) directly to the power in, so if the Pi turns on, there will be voltage on those pins.

The only way there can't be, is if you have physically ripped up or cut the traces running to those pins on the PCB somewhere.
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rhubarbdog
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Re: 5 volt GPIO power pins broken

Wed Aug 22, 2018 2:17 am

To test the voltage on pins 2 and 4 i just use F-M jumper wires and a multi meter. One wire on a ground one on a power pin. Nothing from my 5 volt pins but 3.3volt still ok

pcmanbob
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Re: 5 volt GPIO power pins broken

Wed Aug 22, 2018 9:44 am

As Imperf3kt has said if your pi is booting and you have not done physical damage to the pi pcd to disconnect the 5v pins from the supply there mush be 5v on them, are you sure you are testing the correct pins ?

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mahjongg
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Re: 5 volt GPIO power pins broken

Thu Nov 15, 2018 1:38 pm

If you connect more than 4V (3V3 + one diode forward drop) to a GPIO pin then this can cause latchup in the area of the chip occupied by the GPIO electronics of that pin, this will cause an internal short inside the chip, that will rapidly spread through the chip, and the transistors through which this current runs will "burn to a crisp".

See the latchup section in wikipedia for an explanation of what latchup means.

This is the reason why PI's are not 5V tolerant!

klricks
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Re: 5 volt GPIO power pins broken

Thu Nov 15, 2018 2:03 pm

Rowley674 wrote:
Thu Nov 15, 2018 7:16 am
......
When you connected 5V directly to the GPIO pin....
The OP never said that 5V was connected to a GPIO.
The OP somehow damaged the RPi when removing a HAT so that 5V is not available at pins 2 & 4 and is otherwise working.
Unless specified otherwise my response is based on the latest and fully updated RPi OS Bullseye w/ Desktop OS.

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mahjongg
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Re: 5 volt GPIO power pins broken

Mon Nov 19, 2018 10:29 am

klricks wrote:
Thu Nov 15, 2018 2:03 pm
Rowley674 wrote:
Thu Nov 15, 2018 7:16 am
......
When you connected 5V directly to the GPIO pin....
The OP never said that 5V was connected to a GPIO.
The OP somehow damaged the RPi when removing a HAT so that 5V is not available at pins 2 & 4 and is otherwise working.
True, I might have not read the whole thread, but was triggered by the sentence "The GPIOs are protected by internal diodes, normally reverse-biased and connected to the power rails - 3v3 and ground.", which is not completely true for a PI. There are no official internal diodes, only parasitical ones, and running current trough these can cause latch-up. Just wanted to point that out. Limiting the current flowing into the diodes does not work.

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