The Amstrad CPC used the 6845 CRTC and there were lots of other similar warnings about changing the vertical height too much or reducing the sync widths. At the

The Amstrad CPC used the 6845 CRTC and there were lots of other similar warnings about changing the vertical height too much or reducing the sync widths. At the time, people gave all sorts of dire warnings about the monitors being fried. Years later, I have loads of these machines and several monitors, and the only effect I've observed with out-of-spec sync signals is that the monitor can't synchronise properly and you get the rolling screen effect. So, I think all these warnings were theoretical worries rather than based in fact. Interestingly, it seems some people have also tried to inhibit the CRTC vsync signal and create their own with a similar trick to the PET POKE - see 7.3 on page 40: https://shaker.logonsystem.eu/ACCC1.7-EN.pdf https://shaker.logonsystem.eu/ACCC1.7-EN.pdf (and a comment on page 41 that they have seen damaged chips resulting from this - the PPI is the 8255 bi-directional parallel port driver chip, used on the Amstrad for scanning keyboard, driving the sound chip and miscellaneous such as the VSYNC line).