OK. Progress. Got around to replacing the RAM chip (IC32) and this seemed to be the source of my basic problem with restoring this P6.
Now all front panel controls seem to be working properly, whereas previously, any attempt to rotate a pot caused random results.
It is also possible to get into Manual mode for the first time. As a result, I was able to get thru step 8 of the adjustment procedure, and all Bank and Program switches seem to be working fine, except that once I leave Bank A, it will not return there unless I flip the Tape switch, or power down and back up.
Very few of the program locations have sounds in them, but I assume this is because I have replaced the RAM chip.
My biggest problem now is that output is distorted in an odd way, in which all sounds seem to have the same strange warbled distortion to them. This is a recent problem that has developed in the last year as I have been working on the synth.
Any suggestions about where to look to solve this problem would be appreciated. On the scope, the synth seems to be switching properly on ICs 18 and 19.
Thanks again for the help to all here, and I am very excited that the synth seems to be salvageable. It needs a good keyboard contact cleaning, but now I know that will not be a waste of time.