Polyfuse blown out notes

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I know that anything more than 5v touches any GPIO then it’s dead but I was changing the wiring and accidentally plugged a 12v 2A (for motor supply) connector to a female connector which leads to GPIO pins 20 and 21 for a very short amount of time, maybe a second; ofcourse the PI tripped and got reset immediately.

Now, I didn’t let it power on for a minute and powered it on again. It crashed several times till the splashscreen showing it’s logo and then booted to the desktop finally after few crashes.

I immediately noticed the cpu load percentage on top right being constantly above 25%(unusual) and the power(lightning) logo in the top right stayed there constantly as well so I touched the pi and it was too hot to touch so I immediately switched it off and haven’t turned it on since.

I looked up the internet and there’s mention of a fuse which resets over time but observing the behaviour, my question is, if it boot up to desktop, is it fine and will it reset?

  • Always power down if you meddle with cables and you know that some parts will be damaged if you improperly connect. Double / triple check before powering on. Also, always power down if working with voltages of 50 V and above. – Dr_Bunsen 13 hours ago
  • @BLOODHOUND, Ah, let me see. If Rpi can still boot, but only with a yellow lightning bolt, that means it is only half dead. Yellow lightning means low power. My brainstorming wild guess #1 is (1) Rpi’s poly fuse partially blown out (needs a couple of seconds to completely blown), so resistance changes from zero ohm to perhaps 0.2 ohm, causing a voltage drop from micro USB connector to Rpi 5V rail. You can wait one or more days and see if anything improves. In the mean time, you can try use a multi-meter to off power check the poly fuse resistance, is it self healing etc. / to continue, … – tlfong01 18 mins ago   
  • @BLOODHOUND, If you found polyfuse more than half dead, or you don’t wish to wait, and are going to throw Rpi to the rubbish bin anyway, you can consider replacing polyfuse. But you need to be a ninja DIYer to do ployfuse surgery. A couple of days ago I made it and it took 10 min for the operation: “Rpi3B+ micro USB connector got 15V power. Is it dead? Can I save it?”: raspberrypi.stackexchange.com/questions/104596/… (Don’t worry that much: 15V for one second is OK for the tougher than you think polyufuse guy! :). – tlfong01 4 mins ago   Edit   


A second is not a short period of time for a computer which executes millions of instructions per second.

Neither is it a short period of time to damage hardware designed to handle no more than 3V3.

You have probably destroyed the directly connected GPIO. The damage will likely spread throughout the SoC over time.

Time to buy a new Pi.

The polyfuse isn’t really there to protect the Pi (and would not have helped in this case anyhow as you bypassed the polyfuse). The polyfuse is there to prevent a current large enough to start a fire flowing through the Pi.

  • You’re right. It’s just that the pi booted up fine except it was heating too much. I will still try and power it on see if the temperature rises again – BLOODHOUND 14 hours ago
  • The SoC heating up very fast is a symptom of a failing SoC. – joan 14 hours ago

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