LK4 connects to [[8255|PPI]] Port B, Bit4. The link tells the BIOS whether it should set-up the [[CRTC]] for 50Hz or 60Hz refresh rate.
Default is LK4 not installed (50Hz).
It might be installed in US models, there isn't too much known about whether CPCs were exported to USA.... One source says that the CPC6128 was initially sold ''only'' in USA... Another source says that Indescomp (spanish distributor) produced CPCs with ''Indescomp International U.S.A.'' stickers.
== CPC6128:LK5,LK6,LK8 - Disable 128K RAM Banking ==