Yes, the crystal fitted is a more accurate one, to make the timing more stable for modern displays and converters. IC14, the 74LS245 is changed as a matter of course, as it's one of the known common failure points. It was known to be an issue by Acorn back in the day, which is why some Issue 4, and all Issue 7 have them fitted in sockets for easy change out.
hi mark, you mention the service including the timing xtal and the 74ls245, is there a reason you change these as part of a service?
Yes, the crystal fitted is a more accurate one, to make the timing more stable for modern displays and converters. IC14, the 74LS245 is changed as a matter of course, as it's one of the known common failure points. It was known to be an issue by Acorn back in the day, which is why some Issue 4, and all Issue 7 have them fitted in sockets for easy change out.