Brother PT-1090 Service Manual page 61

As shown below, press/release the cassette sensor 7, 6 and the cutter sensor
in this order in same way.
Cassette sensor 7
Cassette sensor 6
Cutter sensor
After completion of the pressing/releasing the cassette sensor, change the "KEY
submode (4 key*)".
When the NG is judged in either sensor, the machine displays "CST 1 X". Return
to the first checking.
(Change the "CST 2" by pressing/releasing the cassette sensor 2 in the state of
"CST 1 X".)
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