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Upgrading The VGA RAMDAC

The VGA cards for historic PCs have an analog video output that is being driven by a so called RAMDAC. This is an IC that converts the digital framebuffer information into analog VGA signals. Modern PCs don’t need this anymore since they use digital output (like HDMI and DisplayPort) and digital displays. But our old retro machines use this to drive either an LCD or a traditional CRT. There are good RAMDACs out there and bad ones. One problem some RAMDACs have is noise when the VGA palette registers are written. This happens in games and demos for example when the screen is fading in or out. I found a supplier of new old stock INMOS RAMDACs, and I hope that replacing the cheap ADV RAMDAC on my Tseng ET4000 will remove the noise that I am seeing.

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