Why did my Pi die?

Question

So, I have determined that my Pi is dead.

This is what I did in the few days leading up to it:

1.

I used I2C about once every 2 seconds, meaning I updated the display about that often.

2.

I read the temperature of the CPU via cat /sys/class/thermal/thermal_zone0/temp about once every two seconds.

3.

Had my Pi overclocked [Note: I had it overclocked for months before the death of my Pi] to 1GHz and cooled with an externally powered fan.

The last few days

While reading the temperature, my Pi would occasionally crash, various different ways.

Way one: complete crash, all GPIOs forced to the ON state. PWR and ACT led as well.

Way two: kernel panic, resulting in hundreds of panics per seconds comming in on the console via SSH. At this point sudo reboot and sudo halt would not work, and I would have to unplug it.

Way three: system files become unresponsive, like /sys/class/thermal/thermal_zone0/temp /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

Finally:

After formatting a new card, things were going ok, but my overclock settings would not apply. Not until I used force_turbo=1. Then, I tried to install I2C again. I found that the file used to load modules at boot was not being edited by the install via raspi-config. So I edited it myself. My Pi worked again for about 16 hours, and then crashed for good. No kernel panic, nothing. When plugged in with either SD card, the PWR light comes on, and the ACT light flashes like normal, but no wifi, no serial console, nothing. I am currently formatting another card right now.

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Now for my question.

What happened?

Was there something that I specifically did to break my Pi?

Answer 1

From Wikipedia:

Overclocked use may permanently damage components enough to cause them to misbehave (even under normal operating conditions) without becoming totally unusable.

[...]

In general, overclockers claim that testing can ensure that an overclocked system is stable and functioning correctly. Although software tools are available for testing hardware stability, it is generally impossible for any private individual to thoroughly test the functionality of a processor.

I'm not saying this is definitely what caused your problem. However, I think it would require some special tools and expertise to properly diagnose it. Since the Foundation claims overclocking to 1 Ghz is okay, if the Pi is less than a year old, you could try making a warranty claim. But keep reading.

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Although overclocking is not unusual, this does not make it 100% risk free. Electronics do not last infinity years under any circumstances, and overclocking them will probably wear them out faster no matter what, because the major factor in wear and tear is heat expansion. Using just a case fan, you are almost certainly heating things up and down more than you would without overclocking.

Overclocking entails a risk by definition; if it did not, OEM's would stamp their product with a higher frequency. The reason it is possible at all is because the manufacturing process is on such an infinitesimal scale that it is impossible to create chips that have a uniform, exact maximum frequency.¹ In fact, when you buy a 4.0 Ghz Intel Core2 i7-4790K processor, it rolled off exactly the same production line as a 3.5 Ghz i7-4790K. There is no difference at all in the manufacturing process. They are then tested and classified in a process called binning.

The OEM uses this to make a bet about the upper safe limit of an individual processor. Their goal is to make this as high as possible without excessive risk of failure, which will negatively affect their reputation and lead to excessive warranty claims.

So in general, again, it is impossible, by definition, to call overclocking safe. The OEM has already tested the product and determined the safe frequency limit. You are exceeding that.

Note that the Raspberry Pi Foundation is not the OEM of the Broadcom processor in the Pi; their claim that "there will be no measurable reduction in the lifetime of your Raspberry Pi" is just a claim, although of course they have backed it with a warranty. Which you can now make a claim on.

^{1. Put another way, they inevitably vary on an infinitesimal scale in a way that would not be significant with the functioning of, e.g, toasters or flashlights, but is with microprocessors.}