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Video Jitter Fix
Recently it was discovered that there was a previously unknown bug in the Sorcerer’s hardware. This bug, which affected both the Model I and Model II, caused graphics to have noticeable jitter or tearing when there was a lot of processing going on. Resident Sorcerer expert Claus Buchholz explains: "It appears to be a bug in
Exidy's original circuit. The low bit of the horizontal
counter gets loaded from the output of a flipflop which clocks
the E256 signal. The problem is that, during screen access,
that flipflop gets set in order to briefly blank the pixels.
That's by design, and it's why we see the brief, short, black
lines. But a side effect is that, if the access happens when
the counter reloads, the wrong value gets loaded into the
counter, causing a short (by 2 pixels) scan line, and
horizontal jitter on a CRT monitor. When I lifted IC3A pin 3,
the jitter on the scope went away.
Presently, IC3A (IC22A on
the II) pin 3 connects to IC7B (IC17A on the II) pin 9. The
fix will be to connect it to IC7B (IC17A on the II) pin 12
instead."
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