Why is my raspberry pi 2 unstable over SSH?

Question

linux

There is a recently arrived Raspberry Pi 2.
First I tried to upload Raspbian to it. I loaded the card on the CD, turned on the Raspberry, connected it via Ethernet to the router, and nothing. The router does not see it. After a long cycle of "turn on the raspberry, restart the router, take a break", the router nevertheless found it and I was able to connect to it via SSH using the standard login and password.
But that was not the case: after helloworld with echo and python3, I tried apt-get upgrade. And that's all. Zero attention. The SSH connection just stopped responding, stating "Broken Pipe" after a few minutes. The router also stopped seeing it, simply not showing up in the list of devices connected to the router, although the lights on the Raspberry's Ethernet port burned steadily. After several cycles of "turn on the raspberry, restart the router, rest", I reconnected to it, but the problem remained.
It took several days of shamanism, including reinstalling Raspbian, trying on another router, the problem was not solved. Installed Snappy Ubuntu. On "snappy update" the same problem occurs. Tried the method described in the answer here . All the same.
The matter is complicated by the fact that I have neither a monitor nor a wired keyboard to connect to it directly.
UPD. It turned out to be food.

Answer 1

1. No monitor or keyboard required for debug connection. All you need is a one-dollar USB <-> UART adapter that connects to the debug UART of the "raspberry". The second end - to the computer, open the terminal and go!
2. Check the power. Perhaps it is missing.

Answer 2

For starters, I would recommend that you still find a monitor and look at the logs, because there is not enough information. There can be many reasons, ranging from a poor-quality patch cord, misconfiguration and ending with a marriage in the raspberry itself.
I also remember racking my brains with RPi-B for a long time, in the end the problem was solved by replacing the patch cord :)