A15 is the most significant address line, and Leon's test code "might" not need to address anything in the upper part of memory during the running of the test loop. If it is working, you may not see A15 go high. Take the test ROM out and monitor the line... you will probably see it cycle high as the CPU tries to run random garbage. My gut feeling is that A15 is probably not the droid you are looking for...

Yes, by most significant, it means that it determines which half of the addressable memory space is used,,, upper (A15 =1) or lower, A15=0. Also, you are not going to see the line go high at the startup with a volt meter or non-storage 0-scope.

You should consider sending your board to one of the guys that repair them all the time; they have the right tools and knowledge to do it right. "Fixing" it yourself my end up putting the board in a condition where they refuse to work on it.

I would recommend Andrew Spitler or John Wart Jr. Both do great work.

Mac