Sounds like it already had some circuitbending attempts done to it -
open it up and see if you can find some really bad workmanship or
messed up soldering/wiring. I'm really careful that I find out if a
board has previously been bent - you could be buying someone else's
damage - although he would probably deny it if he had said "perfect
condition"

You may be able to undo the damage using the SK5 schematics here:

http://www.jz-server.de/casiology/manuals_s.html

cheers, Graham