Thanks for checking.
It says 1985 copyright on the MCU, right? It must be a reissue, an updated version. Hitachi MCU maskrom serials are ordered chronologially. "C89" can't be from 1983.

I think we can assume that the 1st Portachess had the older program from Sensor Computachess. There is one on this page: http://www.chesscomputeruk.com/html/...tml#Portachess

The difference: it has a "Sound" button.

*edit*
1st version, box says "8 level portable chess computer"
2nd version, box says "16 level portable chess computer" (and has a red triangle in the corner saying "NEW 16 LEVELS")