IBM AT/370 Manual To Operations page 28

6
Make sure that the connectors on the
PC/370-P-M cable are securely fastened to the
PC/370-M2 adapter and the PC/370-P2
adapter.
7
If
the PC/370-P-M cable comes loose, connect
the PC/370-P-M cable to the adapters, one end
at a time. Push the cable connector into the
cable socket until the tabs on the socket lock on
the cable connector (you hear a click).
Tabs in locked position
2-14 AT/370 Option