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Retrocomputing

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    Did test items 1 and 2 on my old CPC464. Results: (1) reproduced. (2) Relay alone is not enough to trigger the effect. Effect can be started and stopped at will by starting/stopping tape motor. So, is it some kind of analog effect, like alteration of sync signals. Perhaps incorrect grounding or motor sucking too much current? Commented Jun 16, 2016 at 15:17
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    I'd wager power distribution on the grounds that subpixel waving is pretty much guaranteed to be an analogue effect, sync is generated digitally, and that one of the cost optimisations of the CPC range is that the monitor and keyboard have only a single power supply. I'd test an external deck and an external screen if possible. Commented Jul 12, 2018 at 15:16
  • I'd propose another experiment: start/stop tape motor while cassette player isn't even connected to the computer. I'll bet it's simple magnetic interference between the cassette motor and the CRT. A CRT display uses magnetic fields to scan the beam vertically and horizontally, and external magnetic fields will move the beam. Commented Jul 12, 2018 at 19:04
  • Thanks for your ideas. For a while, because my monitors don't provide the +12V necessary for the CPC 6128, I have used a cable to allow using a PC power supply. I can test that with a CPC 464 and see if it changes the effect. Probably a few days from now. Commented Jul 13, 2018 at 5:39