Help fixing Vector-06c

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Thank you. This is what I see on pin 15 of the RAMs. I don't think that's right!

In fact this could be a regeneration cycle (pin 15 is CAS, inverted)

Can you monitor pin 4 (RAS, inverted) along with pin 15?

Pin 4 should be low and pin 15 should be high to trigger regeneration.

But anyways the low frequency "envelope" on your screenshot from the oscilloscope does not look good at all.