I've got a few machines using CGA/EGA video; would a serial switchbox pose a problem for switching these machines between a single monitor, or is there some surge or static issue that might damage something?
I've used old clunky mechanical switches on VGA ports many times and never had an issue.
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Mechanical switchboxes are the equivalent of manually unplugging and plugging cables in terms of what happens electrically, but a little bit nicer since shielding ground is usually maintained at all times between all devices, eliminating the surges & sparks associated with joining two connectors at different ground potentials (e.g. floating ground chassis monitors or leaky switching PSUs). It's one of those things that's generally accepted as being fine but with hardware this old Murphy could be lurking around the corner, so YMMV.
CGA/EGA signals are plain 5V TTL which should be buffered and ESD clamped at the video cards and the monitor so it should be totally fine with a decent enough switchbox, but if you want to be extra cautious you could build in some basic surge protection by fitting some 10 ohm resistors in series with each line and some back-to-back zener diodes from each line to shield ground.
