Epson EL 3S/33 - Manual (Page 75)

4. Position the power supply cable connector so that its
notched comers line up with the notched corners of the
drive’s power supply connector. Make sure the holes fit
over all the pins and then push in the connector.
notched
corners
Caution
If you do not align the cable connectors correctly, you could
severely damage your drive when you push them in.
If you installed a diskette drive in the upper bay, it is drive B;
the lower drive is A. However, if you want to reassign the
upper diskette drive as drive A, you can change jumpers J17
through J20. See Chapter 3 for instructions.
4-16 Installing and Removing Drives