And here is a new one for me, don't recall seeing that error message before, nor can I find reference to it in the 9010A Operator Manual. Pressing the MORE key gives me "ADDR BITS 0100 - LOOP?" so I assumed this was some sort of a decode issue and will proceed accordingly. Just thought I would post it here in case anyone else runs across this rare error message which I assume was added to the 3A ROMs in the 9010, but not to the manual - at least the copy I have... (later) It was indeed a problem with some address lines. For only A7 and A8 when loop reading @ 0000 (easiest - all should be Low) with the 9010 probe (set to Address) the Low light was flickering, not steady Low. Turned out to be a 74LS367 that had two inputs that were somehow pulling the lines slightly high. This did not show up when doing a ROM or BUSS test - only in either of the RAM tests. FYI John :-#)# -- How to subscribe or unsubscribe from TTL http://seven.pairlist.net/mailman/listinfo/techtoolslist _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com https://pairlist7.pair.net/mailman/listinfo/techtoolslist FTP site is: ftp://ttl.arcadetech.org/TTL/Test_Equipment Archive site: http://seven.pairlist.net/pipermail/techtoolslist/