Epson HX-20 - Manual (Page 11)

If you purchase an option cartridge containing a program or a
microcassette recorder, then you will need to remove the dummy
cartridge in order to insert the option cartridge. But until then,
please leave the dummy cartridge in place.
When no cartridge is in place, one of the HX-20’s connectors is
exposed. Static electricity or metal objects contacting this con-
nector can damage the HX-20’s circuitry. By covering up this
connector, the dummy cartridge prevents such mishaps.
On the left side of your HX-20, you will notice a small strip of dark
plastic. This covers up a connector called the system bus.
When the system bus is exposed, you will run the risk of dam-
aging your HX-20 through exposure to static electricity, metal
objects, and other hazards. The system bus cover protects your
HX-20. Carefully remove it only to install the HX-20 expansion
unit.
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