Michael J. Mahon wrote:
BTW, a general-purpose design would usually AC-couple the sync signal, to make operation independent of DC levels.
Sure, but this is a brand "A" monitor for a particular brand "A" computer. If it does not interoperate with a competitor's product the marketing department may see it as a "feature".
BTW a friend had an old computer and no monitor for it. On my advice he bought the same 1084 on e-bay for a few bucks. Now his computer had the opposite polarity of the sync signal, but since the 1084's input was DC coupled, I was able to put a transistor into the connector shell as an inverter with no power supply - 1084 provided the power.
-Alex.