Mac Beige C3 to HP 98789A SOG monitor?

Chris M chrism3667 at
Thu Aug 30 19:08:41 CDT 2007

--- Chuck Guzis <cclist at> wrote:

> All,
> I've been digging through my pile of stuff again and
> figured that my 
> old HP98789A 17" (Sony) monitor might be a good
> match my my beige Mac 
> G3. 
> Okay, my next step is to wire up an adapter.  The HP
> is RGB (3 BNC) 
> to sync-on-green.  I read that the Power Macs don't
> support SOG, so I 
> need to combine both the HSYNC and VSYNC with green
> (a couple of 
> 74HCxx gates should do that; I can steal power from
> the sync 
> signals).  Otherwise, it's connect pin 4 to 7 (S0 to
> S1) on the Mac 
> video connector to signal that I want "RGB
> 1024x768".

 There were dookickies that took care of the mode
setting. Some had dials, others dips. I used to have a
bunch, may have come across 1 in recent history. But
mine were a bridge between duh Mac and a VGA-BNC
cable. The info on how to *dial up* a specific video
mode (by shorting 2 pins) should be readily available
on duh net I would think. Macs (older ones anyway) had
to select a video mode at boot, or no video signal
would output.
 I'm surprised to hear that *PMs* don't output SOG.
Depends what you mean by PM. I thought the earlier
models did, but what do I know.
 I used to *cheat*. I would feed separate syncs onto
the green line w/a resistor. Those monitors, of which
there were 2 versions (~48khz and ~64khz) would take
the sync on R,G, or B IIRC. Don't quote me though. It
could be that I was using a video card (aftermarket)
that delivered syncs on all 3. Don't really remember.
 There's a vintage mac usenet group if you weren't aware.

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