Sony csm-20s Operating Instructions Manual page 33

Caution
When you insert/remove a magazine in/from the library, never press the
cartridge lock release lever above the handle. If you do so, the cartridge is
unlocked, causing a failure of the library. When the front door is closed, the
cartridge lock is automatically released.
6
Close the front door.
When the front door is closed, the library automatically starts an operation
to recognize the cartridge.
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Chapter 3 Operation