All that pallaver of swapping corroded 74LS373 (but good) and I'm back
to loss of Data5 and Data7 keys but now D6 keys gone west also,
continuity checks out fine and should be there as before.
D0 to D7, correspond to keys 1 to 8 of each octet of keys, not octave.
So went back to original plan, but now with no D6 to swap to D7.
So cut the trace to D3 input of the 40245 keyboard scan IC and fed the
D7 line to that pin. Powering up, the 4th key of each batch of 8 now
sounded at the pitch of "7" not "3" and midi LED flashed.
So looks like swapping out the 40245, I think, but perhaps wrong, as it
seems functioning correct signal on D7 line but not getting through the
40245 nor D6 nor D5, input to outputs , for keybd scan.
Pitch number 8 of each octet would sound (and 6 and now 5) , if the
keyboard scanning funtion was working correctly, I hope.