Adapting digital RGBI monitor to accept analog RGB

Alexis Kotlowy thrashbarg at
Tue Jun 14 11:34:00 CDT 2016

On 15/06/2016 01:32, Eric Christopherson 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 just that *somewhere* on the web a few years
> ago, even though I can't find that mention now.
> ...
> So... does anyone know if these monitors can in fact be made to
> accept analog RGB? Or have a way I could tell after opening them up?
> And, of course, I'd like instructions on just how to do it, if it is
> possible.

The schematic details the TTL interface stepping down the 5V levels to
0.7V analog levels, which get sent through three capacitors, C217, C218,
and C219 (all schematics) to a CRT driver IC (IC502). If you were to
correctly terminate and buffer your analog RGB levels first, you'd only
need to feed those signals into the driver IC. The sync signals for
analog RGB are usually at TTL levels anyway, so they can go to the
normal inputs.


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