You doing all right.
about avionics - there is a kinda trick with this aircraft. avionics can shut-down inflight. That'll cause AP to fail.

check this topics on this forum -
http://www.captainsim.org/yabb2/YaBB.pl?num=1315183931 - there is a links inside.

avionics easy to check - just look at GPS, if its dead - then thats your story up in the link. if avionics on - i dont know then :) gotta think more on possible cause of that strange AP-piloting.

keep it up! thats an old bird. something needs to be fixed :)))
dont miss pressuration system fix from member Dutch. He's kool in fixing stuff :) its on this forum also.