On Fri, 24 Jun 2016, Fritz Mueller wrote:
In bringing up and debugging my PDP 11/45, I found that one of my GRA (M8101) spares has a failed ALU subsidiary ROM. It's a pretty standard little 32x8 ROM in a 16-pin DIP, and the truth table is in the 11/45 print set.
Some years ago I had to replace one such PROM in my 11/45 that is responsible for the ALU conditional codes. Since the PROM contents is quite simple, I replaced that with a GAL with the corresponding logic equations. Not a pretty solution, but I can replace it with a new PROM when I get one. A similar fault was in my RK05 "Cylinder Address and Difference" board, also changed the failed PROM with a GAL. The symptom was that the drive never "found" the desired track and instead, bumped the carriage to the inner stop.
Christian
