I a using as raspberry pi 3 model B and I think I have tripped the poly fuse as I connected it to a nine volt battery pack and a 5 volt extension. I waited for the poly fuse to reset itself for like six to seven days but after that I have no luck....So I started to wonder if there is a way to manually reset the poly fuse. my mother is saying that we should get a pi zero or replace the poly fuse.(PS- my mother is the best engineer and programmer I have ever met). so I told her that I would post the Query here on how to reset the poly fuse. Please Help this is my last hope or goodby Raspberry Pi 3.....
The polyfuse will not protect you from connecting 9V to the Pi. Its purpose is to limit current, not voltage.
The Pi is likely dead, having been destroyed by the application of 9V.
If the polyfuse had operated to limit current it would have recovered after a day or so.
It is never safe to feed over 6V into any Pi, regardless of whether they have a polyfuse fitted or not.