-  A substitute for defective logic!
    One example : remove the (defective) boards from the
    card reader (DEC aka Documation M200) and replace it
    with a single Core and I/O board (+ software...) 
I sometimes wonder if I'm the last person left who can actually do
fault-finding!.
Put it this way, it's a lot easier for me to find the dead chip in an
M200 (or in anything else for that matter) and replace it than to fight
with some FPGA-based thing...
-tony