From Brian Willoughby Sent Sat, Mar 10th 2018, 01:41
Thanks for the report, Michael. Should be great information for the = archives. Meanwhile, I had intended to respond to your earlier message about the = =E2=80=9Cbad=E2=80=9D Z-80 with a hypothesis. I recently repaired a = Roland CR-78 where one bit of a latch had partially burned out. The = whole thing was working except for the Bass drum, and I tracked it down = to that one bit. My thinking on the Z-80 is that it must have been = mostly functional if it was able to run the synth apart from tuning, but = perhaps there is a Port IO pin that is exclusive to tuning and which had = gone bad. Not that you can repair an individual pin without replacing = the whole chip, but I was curious. Typically, a CPU is either completely = dead or totally functional. It=E2=80=99s actually quite rare to have = some features fail while most are still working (at least not unless = there is a bug in the firmware - in which case the same problem would = appear on all units). Again, thanks for detailing your work and discoveries. Brian Willoughby On Mar 9, 2018, at 5:32 PM, Michael E Caloroso = <xxx.xxxxxxxxxxx@xxxxx.xxx> wrote: > The last mile to the finish line was the toughest... autotune > wouldn't. Even though the display reads "6 TUNED" does NOT mean that > it tuned the VCOs! After isolating many of the support ICs and > confirming the audio path between the VCOs and autotune circuit the > root problem turned out to be.... the Z80. EVEN THOUGH THE REST OF > THE SYNTH FUNCTIONED.