After much research and trouble, I came across a TomTom schematic diagram. It turns out that U30 is the Bluetooth chip and (see photo) mine is physically damaged, probably by someone careless with a screwdriver when changing the battery! I confirmed this on another I have which does work and U30 doesn't have the corner of the chip missing.

So at least that answers one question U30 is the Bluetooth controller Ic

CSR BC41B143A05

Thanks again for the suggestions Quin.

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