> 11Hz, 10 nsec flanks

That is a bit too fast imho. Is there any overshoot or undershoot ? Do you
drive it with LSTTL or rail to rail (don't !). If you drive rail to rail
it may help to limit the H level to Vcc - 0.8V. It may also help to add a
small resistor (~100R) and a 47 pF cap to GND in series with the clock
wire. Just in case there is ringing.

I assume that you did try other chips from the same series ? Who is the
manufacturer of the chips ? ;) Yes, I've had it that way too. <g>

Peter

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