Rich Cini said "not letting it reset" means the S-100 system works without the board, but doesn't work with the non-working board inserted. Rich, I think that means the board crashes the bus, not necessarily that it screws up reset. On the "no data on select" board; I think you are telling me, you confirmed chip-select on say the FDC chip is properly enabled. But you say changing bus buffer chips and the FDC chip doesn't change your results. It may be inconsistent bus timing. S-100 bus timing depends on the specific CPU board (and front panel) versus the board under test. If you've never used a Tarbell DD board in that S-100 box, and two don't work, and the data you read is a persistent incorrect value; mismatched timing is a possibility. S-100 control/status signals also depend on chip delays and even R/C circuits which age poorly. I see your point in using a bus analyzer, to look at all relevant signals. I look at signals with a 2-channel oscope, one channel often on the bus clock or other timing source. For home-gamers reading this: note that I'm saying that S-100 is not a single, consistent "standard". S-100 cards don't all play well with each other. I claim three flavors of "S-100" bus, on my Web site; early Altair, S-100 MITS/Altair/others, and IEEE-696. "It worked previously" points to corrosion problems too. Look for TI brand chips which have blackened pins; they seem to fail after a period of recent use. I chased this down with my Ithaca Intersystems repair. That happens across S-100 cards with socketed chips. http://www.retrotechnology.com/restore/ith_feb16_repairs.html Rich, contact me privately for further discussion. Chasing chips is boring for many people; they can read your results on your Web pages. herb -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info