Rik Bos wrote:
  I'm bussy restoring a Ti SR-52 and having some
trouble with the card reader 
[...]
  So I'm searching for a schematic diagram or
service manual. 
I had a paper copy around 1979, which wasn't too hard to get at the
time.  IIRC, I just called TI's Lubbock, TX office and asked for a copy,
and they sent it to me.  I doubt that they have them any more, but if
they were easily obtained (unlike HP calculator service manuals), there
are probably people out there that still have copies.
The TI-58/59 service manual is more commonly available.  It's possible
that the card reader is similar enough for that manual to be useful to you.
Eric