A little additional corroboration of the remarks already made about the Classic model M1420, from two of mine:
CK1128HBD11—Mar. 1991—Clinton CRT—Type A Analogue board
SG23403RD11—Aug. 1992—Samsung CRT—Type B Analogue board
The Singapore example also has a rectangular blanking plate on the case bucket, over a circular port hole to the left of (seen from behind) and slightly below the ADB port. A further distinction between early and later production is the circular pattern of ventilation holes at the front left side of the case (seen from the front) for the speaker. This latter distinction is common to Classic and Classic II, but I cannot yet assert that it corresponds with, say, the analogue board change:
SG2010ZAD25—Jan. 1992—no sound vent
SG3207THC2G—Aug. 1992—sound vent
Note also, that in defiance of the printed year of manufacture above the serial number, the newer Classic II's serial number begins 'SG3...', indicating 1993. That could be because the first and second digits have been transposed. Re-transposition of the first two digits would better correspond with Aug. (week 30) than does the present week 20 (May) of 1992.
de
CK1128HBD11—Mar. 1991—Clinton CRT—Type A Analogue board
SG23403RD11—Aug. 1992—Samsung CRT—Type B Analogue board
The Singapore example also has a rectangular blanking plate on the case bucket, over a circular port hole to the left of (seen from behind) and slightly below the ADB port. A further distinction between early and later production is the circular pattern of ventilation holes at the front left side of the case (seen from the front) for the speaker. This latter distinction is common to Classic and Classic II, but I cannot yet assert that it corresponds with, say, the analogue board change:
SG2010ZAD25—Jan. 1992—no sound vent
SG3207THC2G—Aug. 1992—sound vent
Note also, that in defiance of the printed year of manufacture above the serial number, the newer Classic II's serial number begins 'SG3...', indicating 1993. That could be because the first and second digits have been transposed. Re-transposition of the first two digits would better correspond with Aug. (week 30) than does the present week 20 (May) of 1992.
de