Multiple problems with my Raspberry Pi 3

Question

I am not new to the Pi 3 and now have it for quite a few months now. However, I started to face multiple problems:

1. My pi 3 would shut down and restart when I was working on it. At a time, only the red light came on and the pi did not start. I had to change the micro SD card and re-install it with NOOBS. It did work after that but only for a day and then the same problem arose again but with a voltage issue which I have written below.
2. When I connect my Raspberry pi to power, it suddenly gets very, very hot and only the red light glows faintly. It is not even starting up. I connected it to 5V only using the official adapter but it will not power up. All three chips get very hot.

That's all. If anyone knows what to do, please help and be very specific.

Answer 1

it suddenly gets very,very hot and only the red light glows

This is a very bad sign. I think the only chance you have is if you have blown the main polyfuse -- although unfortunately if this were the case I think it simply would not turn on.

However, I've never examined a pi where this happened, and as mentioned, this is the only possibility with a good outcome. At least a few people here have reported doing it, allowing the polyfuse to reset, and having a working Pi again.

That simply means leaving it unplugged for a day or so. If after that you still get the same result, unfortunately you are out of luck: The Pi is defunct.

If you are sure this is not your fault you could always try making a warranty claim with the retailer (or the Foundation itself, presumably they can handle that).

Answer 2

To enhance goldilocks answer, there is a PTC at the power input micro USB connector.

PTC "F1" will trigger (or temporarily blow) if the Raspberry Pi consumes more than 2.5A. This means it would only blow if you overload you Pi with multiple USB loads that are >= 2A (some power is consumed by Pi too).

Also as per the datasheet of F1 (MF-MSMF250/X), it has following threshold levels. The fuse holds at 2.5A and trips at 5A.

If there is a lot of load connected to your Raspberry Pi there is a chance that polyfuse F1 will trip. Usually a polyfuse resets within minutes after disconnecting power and load. It depends on the temperature not time. If it cools down fast, it will reset fast.

A bad power adapter will mess-up things as well so make sure you have a good quality power adapter and no load (no USB peripherals or any GPIO load connected) when testing you Pi.