I just read the post of David you mention. By a "jumper" I think he did not mean a physical jumper, but a wire to be added between +8.5 and? the resistor at pin40 of IC1 (YM26600). By the way, beware that in the service manual of the CS80, the numbering of the pins of IC1 and IC2 on the KAS board (page 5) is erroneously done the other way round ! Pin 40 is the one labelled 1 and vice versa.
So, you'll have to unsolder the extremity of the 22k resistor at pin 40 (the one pointing toward IC2) and then solder a wire between this unsoldered extremity and the +8.5V point of the KAS board located close.
I posted an excerpt of the KAS diagram where this is illustrated here:
As for unsoldering the whole board, that is something I would try to avoid. Just swap the defective component between the M-board where it is now and the M-18 or M-28.
