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I asked a question yesterday about my Sony Xperia Z1. It look likes it is completely empty and I don't have the ability to flash anything on it.
But my question is:
Can you break your motherboard by rooting, flashing or whatever?
My custom ROM (PAC-man ROM) worked perfectly fine until I restored my TA partition.
My previous question:
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Nice question! Short answer: Yes and no, it depends on how a device is designed.
One needs to now how a device initially boots and look at the involved components to be able to answer this question. To get an idea, here are some examples from my memory:
All newer Google Nexus devices (except the Nexus One) are pretty much unbrickable.
Most Samsung models for example have their bootloader on the eMMC chip: Brickable
To unbrick, one needs an alternative way to boot from e.g. USB to fix it (this solution exists for the original SGS i9000, but there's currently no way to do it with later models)
Sony Xperias have the bootloader in non-writable mask ROM: Unbrickable.
You could delete the whole eMMC chip and still boot into Flash Mode or fastboot mode (needs model specific key combos on boot), unlock the bootloader or use their software (PC Companion) to revive it. See Androxyde's FlashTool and Sony's FlashTool.
Raspberry Pi's have the bootloader in mask-ROM which then boots from the SDcard: Unbrickable
(Well, this is not a real Android device per se, but you get the point. PS: The Pi can be damaged by overclocking)
Some Samsung eMMC chips have faulty firmware: Brickable (source)
A way to fix it has recently been found but it's very risky and only tried by one of the devs. CyanogenMod's Wiki has more information.
The original HTC Magic had its bootloader on the eMMC: Brickable
In general: If one part of the chain is breakable (without the ability to revive it), you can brick your device. For example, it's possible to get into a catch-22 situation where no further action is possible (e.g. unlockable bootloader + broken system&recover) although the device would still boot to the bootloader.
Yes, it is possible to hard brick your device if you do anything wrong with your TA partition. There are loads of threads in XDA-developers warning people not to do it if they are not confident.
Few examples of backing up TA partition threads here.
Loads of warning when they advertise these methods.
Fair warning: Flashing your TA partition is dangerous stuff, do this wrong and you can most certainly hard-brick your device. I will not take any responsibility at all for anything you deem might have (or might not have) been a result of these procedures, be it bricked devices, lost DRM-keys...
Apart from the risk of breaking your bootloader, which others have mentioned, there are other ways a custom ROM can destroy your hardware. For example, you might install a kernel that has no or misconfigured power management support. In extreme cases, this might cause the CPU to overheat, damaging it permanently.
