Graham,
I can confirm noise/spikes on mains connection to the TYROS causes an unwanted signal over the USB that locks-up the PC's USB circuit. I can reproduce it by switching on equipment like TL Lamp. I have tried it with other battery powered PC, and also moved the TYROS to another wall-outlet, it proved the TYROS picks up the spikes on the mains connection.
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Cheers
JaapV (NL)