For a start you like to mention what country you're in?, certainly in the UK Hitachi don't make any TV's, Hitachi sets are just cheap Vestel models re-badged - many of which have nothing to with Hitachi (they sell the name to retailers, to put on anything they like).
If it is a Vestel, then the schematic is most probably available, and can be found using the Vestel number off the PSU PCB - otherwise, it's VERY likely there's no schematic available at all, most sets in recent years don't have any schematics available, even to official service agents.