This code does not appear in the official Sony manual. It may indicate: 1. display bug or incorrect display of another message. 2. low or empty back-up battery ("" icon normally provided). 3 Software problem or fault.
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🔧 Steps to try 1. simple reset: - Disconnect the alarm clock from the mains. - Remove the CR2032 battery. - Wait at least 30 seconds. - Replace the battery and reconnect. 2 Replace the CR2032 battery with a new one, even if the old one seems to be fine. 3) Factory reset (via the alarm clock menu) to clear any software errors. 4) Observe when ErrU56 appears: at start-up, during a setting, or after a power cut. 5. contact Sony support if the message recurs after these steps.