OSD can be generated in the micro or jungle IC. The data was stored in an
E-prom usually. Zenith was the only teletext builder I know of here in the colonies. It was in digitally processed NTSC sets ( ITT chip set ). Cant help there as all the digital stuff was on a module w/ plug in IC's so that would be swapped out.
Looking for cold joints & unseated connectors a good start. Especially watch
the plug / sockets of sub boards & input jack packs. And always watch for bad
hook up cables !
Also look up the data sheets on the jungle IC that can give you a good
idea of where the I/O's are & more
Hope you get her going again. Let us know how you do.
Cheers
Zeno
LFOD !