DEC 3000 (alpha) faultfinding

It turns out that jumpers J8-J1 select one of the d0-d7 outputs from the 27C512 which contains the eight SROM images, one per data line. One of the positions must be jumpered or no SROM image is loaded and nothing happens. (Nothing much seems to happen with the jumper in the J1 position either. Maybe there is no image on the d7 bit or maybe the there is an image there that doesn't drive the either the mini console port or the diagnostic LEDs.) It also turns out that I had an intermittent bad connection in my hacked up mini console interface. This is why I was not able to enter commands with the jumper in position 1 (J7) or position 2 (J6). With this fixed, I can enter mini console commands with either of those positions jumpered, so they seem to be the ways to access the mini console on the 3000 600 machines anyway. I ran the various tests provided by the different jumper settings on my second 3000 600 and I found that the memTest (no-cache) LongWord Memory Test (position 5, J3) failed as well as the tests involving the cache. In an attempt to find which memory was failing, I swapped around the memory risers. Bizarrely, the (no-cache) failures went away completely when I swapped around the front two risers. The failures returned when I swapped them back. This is very odd as the two risers appear to be identical and seem to be populated with identical SIMMs. Regards, Peter Coghlan.