The SCSI cable is backwards. I ran into this a few weeks ago. You should also think about cleaning the heads. The easiest, totally non-obvious way is pop the two C washers (with the power off obviously on the head stack, and pull the stack up to gain access to the head surface. Clean with "head cleaner" if you can still find a bottle, or 99% isopropyl -- TK50 media sucks.. I just had to read several hundred carts from the mid 80's and every one was sticky. The REALLY annoying thing about serpentine media is you get to spread accumulated gunk across the ends of the tape after each pass, and risk the motor stalling and leaving a big pile of gunk after each direction reversal.