LEXICON 300 repair... need some help NO Digital Inputs available.

Hi, I tried to connect  my Lexicon 300 (no LARC) with AES /EBU Digital input but the Lex don't want to lock to external WC. On all  inputs : Optical , RCA , AES no Digital input is found. The message still flashes BAD /Input connection.... I tried with several
AD /DA Converters , cables ....Frequencies....

I have a second Unit I changed from there the Digital I /O Board. This makes no difference.  BAD Connection Message still appears.
All parameters 100%  correct settings. 

Any Suggestions.??

Thank you guys in advance

Whenever I hear 100% correct settings I immediately think that is suspect. if all was correct it would be working   Plus we often want to look for the really hard problem because we feel dumb when we miss the obvious stuff and super smart when we catch the hard one.  No worries. Here is a link to the manual below.  Read chapter 3-3 on setting up the unit to work for digital I/O.  While I am sure you did set it correctly you may have missed something. I also suspect setup as you swapped digital boards and had no change. It would be odd/uncommon to have 2 X digital boards both having an issue.  I would also check your machine and converters feeding the 300 via digital I/O, there may be a setting there that is off.

https://3e7777c294b9bcaa5486-bc95634e606bab3d0a267a5a7901c44d.ssl.cf2.rackcdn.com/product_documents/documents/1065_1340211646/300_V3_Owners_Mnl_Rev2_original.pdf