You can find the schematics on the HP computer museum
site
http://www.hpmuseum.net/exhibit.php?hwdoc=51
And if you are a member of the HPCC you can read Tony's excellent
repair manual which was published in the DATAFILE journals of the HPCC.
If you're not a ammember of HPCC< you can jsut ak me nicely for it. It
comes as a .tar.gz of LaTeX files...
-tony