That pesky Jupiter Ace *still* won't work...t

You have a 'scope, and the outputs of the timing chain should be pretty regular, so it's not hard to ensure it's clocking correctly... You have checked the CPU clock, etc, are presnet, right? An ohmmeter ? :-)... Check for shorts between adjacent pins/tracks, and the like More seriously, look for signals on RAM pins that don't look like clean TTL signals. If you find any, make sure you have not got 2 signals shorted together. You mentioned earlier that the ACE only loads the chargen after checking program RAM, etc. What does it do if the test fails? HALT? Goes into a tight loop? Can you see if it's getting there with the 'scope (if it's a tight loop, most of the address pins should be static, at least during MREQ cycles). -tony