
Post-mortem: MRI disables every iOS device in facility - Lx1oG-AWb6h_ZG0
https://reddit.com/r/sysadmin/comments/9si6r9/postmortem_mri_disables_every_ios_device_in/
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Lx1oG-AWb6h_ZG0
This is one of the weirdest corner cases I’ve heard of, right up there with
the famous 500 mile bug. /u/captaincool diagnosed the issue a few weeks back
(confirmed by OP today after talking to apple):

> It's definitely the helium.

> The processor in a modern, high volume device typically has its main clock
> driven by what's known as a MEMS oscillator. These are barely visible
> mechanical systems that resonate at some designed frequency, and include
> packaging to convert this resonance into a useful electrical clock signal.
> These devices are extraordinarily cheap ways to produce a steady clock, but
> they have a number of drawbacks. Most relevant, in order for these types of
> devices to function properly, the mechanical resonator must be inside a tiny
> hermetically sealed chamber with either a controlled gas inside or a vacuum,
> as the gas composition in the chamber can affect the output frequency.

> For both cost and physics reasons, these hermetic seals are not perfect, and
> are somewhat commonly permeable to small atomic gasses such as helium.

...

> For this specific case, Apple devices probably share a common family of MEMS
> resonator to reduce manufacturing costs. This clock likely leaks in helium
> rich atmospheres, pushing the output frequency outside of the bounds that
> the main processors are designed to handle, rendering them non-functional.
> If left idle long enough, the devices may begin to function again, but
> depending on the concentration of helium which leaked in, this could take
> anywhere from weeks to years to occur in natural atmosphere and
> temperatures.

[https://www.reddit.com/r/sysadmin/comments/9mk2o7/comment/e7...](https://www.reddit.com/r/sysadmin/comments/9mk2o7/comment/e7g5rcw)

