The Miura reader has a tamper detection system to detect
unauthorised manipulation of the reader hardware (e.g. to eavesdrop
on the PIN from the shopper).
The detection system for example triggers when somebody tries to
crack open the case or when the reader is dropped onto the floor
hard. Once trigged, the Miura display will only show TAMPERED and
will cease to function.
In this case please ship a new reader to the merchant.