[8)] ]'> I just noticed that the low level signals to and from the heads are carried by flex PC conductors terminating in tin plated connections (at least on my current SE/30 reference unit). Over time, this is known to be NOT GOOD, leading to intermittent and/or poor connections. To test, simply unplug and re-insert both head connections and retest. Probably not a bad idea to reseat all of the other connector pairs also. Low voltage/low current tin to tin connections are vulnerable even in clean lab conditions, and especially so if the machines are stored in uncontrolled climate extremes (any of these where you live?).