The 468 Digital Storage Oscilloscope used the Mostek MKB36000 ROMs which are known to deteriorate over time (e.g. FROMs - Forgetful Read Only Memories).  The only remedy is to replace the ROMs with EPROMs.

The Motorola MCM68766 is pin compatible but generally unavailable. The more common 2764 requires an adapter board to convert the 24 pin ROM socket to a 28 pin EPROM socket.  Space can sometimes be an issue but the 468 has ample room for adapter boards. These adapter boards also have provisions for using larger EPROMs as even the 2764s are becoming harder to find.

We sell a pair of programmed EPROMs with adapter boards on our eBay store.