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Raspberry Pi Fuse - Have you ever tripped it?

Sean_Miller

I got a little sloppy and threw a spark on my Raspberry pi.

 

After, the SD card light shows no sign of life and the SPI Display somewhat flickers.  It never boots.

 

Google quickly showed that the fuse is self healing over what could be minutes, hours, or even days.

 

So, my question is - anyone ever trip their fuse?  How long did it take to function again?

 

-Sean

  • I will admit to shorting the 3.3v pin to ground on the header.  It was a while ago, a Pi 3, and it never came back. image   I'm hoping you have better luck.

  • The self healing properties of the polyfuse normally doesn't take all that long to at least get back to a functional state. When it trips, it gets warm and needs to cool down to restore its original resistance, but even without a full restoration it should still be okay to boot again in a relatively short period (minutes) assuming your downstream load is not high (i.e. attached bus-powered USB peripherals). Depending on where/how the spark came about, you could have done some permanent damage - rail to rail (e.g. 5V to 3.3V) are known to be likely to be disastrous.

     

    The polyfuse does have some headroom to allow for some USB downstream loads - so if after the event, it still won't boot with minimal/no downstream loads, you may well have a dead Pi. To confirm, you could (at your own risk) power through the GPIO pins from a capable lab supply which would bypass the polyfuse altogether, or as I've done with some of my Pis, remove and short over the polyfuse connection altogether (mainly so as to power heavier downstream loads in my instance).

     

    But perhaps also worth preparing a known good mSD card to test with as sometimes improper powerdown can lead to unbootable cards ...

     

    - Gough

  • I would test the polyfuse first make sure it wasn't the issue if it is one thing you could do is replace it or just bridge it if you really wanted but I don't recommend. 

     

    you should be reading 5 volts on both sides with a small drop on the one side this is normal.  I just tested as well since I had one on my bench it is a 267T one which is 2.6amp from what I came to understand.

     

    For a dollar for the part it might be worth finding a replacement 2.6amp polyfuse.  I am going to say its probably a max 6v as well.

     

    and it could be late and I am just talking out loud again? lol

  • in reply to gam3t3ch

    Gave it a day and no luck.

     

    I actually think I zapped outside of the poly fuse.  Looking at the schematic, it appears the polyfuse is off the USB power in.   I was powering with the 5V pin.

     

    However, I think I actually zapped it by putting 16V through the headphone jacks ground .  :-)

     

    I was trying to get the hum out of an LM386 amplifier circuit and thought I'd power it from as close to the battery as possible to see if that made a different. 

     

    Boy did it!  No more hum, that's for sure.

     

    Oddly, when I put the 5V rail on the O-scope, it cycles between 3.3 and ~5Vs consitently.  In turn it cycles 600mA and 400 mA just sitting there dead with a red LED.

     

    Would be interesting to fix, I guess, after I get my project back together with another PI.