Adapting digital RGBI monitor to accept analog RGB

Eric Christopherson echristopherson at
Tue Jun 14 18:09:55 CDT 2016

On Tue, Jun 14, 2016, tony duell wrote:
> > I am in possession of two Magnavox (North American Philips) CM8562
> > monitors. Out of the box they handle composite and digital RGBI (CGA)
> > input. What I'd like to do is get one to handle analog RGB (like arcade
> > boards, Amiga, Atari ST, and Apple IIGS put out). I wouldn't think this was
> > possible, but I seem to have a certain memory that I saw mention of doing
> My guess is that it is possible. The CRT is an analogue device. There must
> be circuitry in the monitor that accepts the 4 digital signals and turns them
> into 3 analogue signals to feed to the video amplifiers. So you should be
> able to feed in a suitable analogue signal after said conversion stage.
> Last time I was inside a similar Philips monitor, the main PCB was designed
> for all possible versions, but only the necessary components were fitted. If
> you can get the service manual for the version you want (with analogue
> inputs) compare the PCB layout with the version you have to find out what is
> missing.
> When I had to do something like this, the hardest part was finding the
> right switches and connectors that would fit on the PCB and line up 
> with the holes in the case.

Thanks to both of you. This might give me a goal to work toward while
learning electronics.

Is the 15kHz RGB signal fundamentally the same as the VGA signal, except
at a lower horizontal frequency? If not, how do they differ?

        Eric Christopherson

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