Quoted from PBFan:Are you sure your optos 91, 92 and 93 are installed correctly on the assembly? If they are not in the right order then it will totally confuse the MPU and resulting position. Did you remove them at some point? The guide previously mentioned will show the correct location for them.
This is a restored machine. The restorer has a sterling reputation, but I guess mistakes can be made. It is worth checking into.