50Hz vs 49Hz - Vintage Polish Computer Terminal

[AlanInSitges]

IME the 1Hz difference won't cause much if any problem. But if that thing is designed for 50Hz and running on 60Hz, the ripple from the power supply will beat with the vertical scanning frequency and cause the image to vibrate quite a bit. I have a Predicta and a couple of PortaColors here in Europe that are unwatchable when fed a 60Hz NTSC-M signal but running on 50Hz. N.b., Shango did a video a year or so ago where he solved a similar problem of trying to feed a modified 24FPS signal from a telecine to a Sony TV and ultimately I think he fixed it by adding a ton of capacitance to the power supply.

In your case I suspect the problem is more likely related to the cheap inverter you're using - they call them "pure sine wave" but they are neither pure nor sine wave. Most of them output a messy "modified" sine wave that will wreak havoc with the old linear power supply in that terminal. They look something like this:


There are evidently some that output a cleaner form of AC but I have tried two different ones sold as "pure sine wave" that looked that way. TV's don't like them, and neither do 60Hz motors in record changers, at all.

If I were you, I'd try using a 2:1 autoformer (these are fairly cheap) to feed 220-240V 60hz power to the terminal and see what happens. Going from 60Hz to 50Hz is difficult because of the higher ripple coming from the power supply, but going the other way might not be as bad, or even problemmatic at all. At the very least you'll be able to tell whether the issue you're seeing is due to the dirty AC power from the inverter or a failure in the terminal itself.