Re: IIgs Analog Video Circuitry

[Kevin Dady <kevin@hackaday.com>]

On Sep 28, 10:31 am, Daniel Kruszyna <d...@krue.net> wrote:
> MdntTrain <j...@cimmeri.com> wrote:
> > I don't have my schematic handy, but two types of chips (post the VGC)
> > contribute to the rear port signals: there is the RGB-> NTSC converter
> > chip around there (I believe it's the MC1377 or similar), and then
> > there's the video D->A converters (DACs).  I'm not sure whether the
> > DACs are off shelf.
>
> Each 4 bit component of the VGC output is first connected to a smaller SIP,
> which I believe is an R/2R ladder DAC. From memory, the DACs are marked H2, H3,
> and H4. It's the analog outputs of these three DACs which are then input to the
> module in my original question. Apologies for not providing this detail
> earlier.
>
> -- Daniel

its probably some form of summer, you generally cant take a bunch of
voltages and simply wire them together and expect them to work
(correctly), and yes if its a epoxy blob sip IC chances are its
custom, even if its not good luck finding it unless its a scavenged /
nos part...

Is yours broken?