Thank you for the valuable information that was exhibited in Yahoo auction in 2005.
The serial number is 79 1370, so I think it's 1979, but when you open the circuit there is also a handwritten character that says 1980/6,
I'm asking MICA for the exact date of birth.
Also, the case was made in Japan when Yamaha was an agent.
In any case, thank you for the information.
From Y.H.