Hi, I think your info from Toshiba is a mis-print and should read D817!(DIODE UF5408)which is the Line supply diode(which I presume means HT supply to Line stage)
Look for problems on Primary side of PSU, including dry joints around Q801, D810. Secondary side, C845 may be bulging, IC800 and IC801 may also need replacing. The fault may cause R804 or R856 to show signs of overheating.
This diode has been upgraded from 800v to 1000volt
The new part number is V30034072
DIODE UF5408
Hope this helps