The sine wave is a sawtooth on the screen. The modulation is in the Z axis. These two make it sound like ripple in the power supply. I have worked on these and found most of the 1mfd axial tantalums as decoupling on the boards to be high in ESR. I replaced them with radial film types. In a few spots, I put in 22mfd tantalum to boost the decoupling. I had these in stock and used them. The main filter cans and decoupling from the regulators could be going bad. At the age of this, condensers going bad is likely. The cans are a pain to get out and reinstall. Restuffing is not hard, for me. Since the flicker stops at slower sweep speeds, dirty contacts are possible. Some resistors, mostly the carbon ones, are too small in wattage. It is possible some have gone high in resistance. Heather-cathode leakage in any of the Nuvistors?
Mark
