The HB725 and HB730 were very similar electronic organs made by SIEL in the early eighties. The schematics are in two parts :
An A3 sheet titled "HB 730 schematic diagram". Quick and dirty scans there.
An A1 sheet (8 folds) titled "HB 725 - HB 730 schematic diagram 3rd edition". Not scanned yet. If you need it, drop me a mail.
This is http://www.teaser.fr/~amajorel/hb725/, last modified 2011-02-14.