I sure hope I'm misled as you suggest, but both feeds are most certainly carrying NTSC signals.
I should have been clearer, however - on the block diagram screenshot, the multiple instances of the Ref portion that are shown don't appear simultaneously - they randomly flicker between each other. So although I'm pushing NTSC black into the IoHD, that's only intermittently being reflected in the Ref portion of the control panel's block diagram.
The time base fluctuates on these 30yo tapes, so feeding the NTSC black burst into Ref is intended to metronome the video into lock-step.
In any case, I tried pulling the sync gen outta Ref and let the IoHD use the poor old video as the sync source. The block diagram in the AJA control panel remains flickeringly unstable :-(
Since you are working with a VHS source, you may wish to consider the use of a time base corrector (TBC). This tool would help stabilize the signal coming out of the source VHS deck before it is sent to the Io HD.
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