sync on green to horizontal and vertical wiring seperator.

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Jun 11 04:20:14 2001

The place to look for the signals isn't in the monitor, but on the video
generation circuitry. If there's a horizontal and vertical sync available
anywhere in your video generation circuitry, you'll want to measure their
durations and frequencies, as well as polarity. There may not be separate sync
at all if it's generated as composite sync in some specialized IC. That's
adequate for sync-on green, but if you want to attach a PC monitor you'll have
to go to some trouble.

You can generate the negative-going sync most easily by using a negative supply.
If you use a current mirror controlled current sink that pulls the 75-ohm
resistance to ground down by half a volt or maybe 3/4 volt, and then use a
diff-amp made from a couple of transistors to switch the sync on and off, you
can get negative sync from one transistor or the other's collector. Clamp the
base of one (depending on the polarity of your sync) to gnd with a schottky with
about 0.3 volts forward voltage, and limit the current at that base with yet
another transistor also controlled by the current mirror, such that the voltage
at the base of these transistors ranges from as high as the clamp will allow, to
about the same amount below gnd, by limiting the current from the sync signal,
with a resistor, typically 1K-ohms. attach the appropriate transistor in the
diff-amp to the green video. Set the current in the transistor that sinks the
current from the diff-amp to such that the sync voltage is about half a volt
below ground. If you need more details, let me know. I normally use VERY fast
transistors in a 5-transistor array (CA3127/3227) to do all this. A CA3183
would probably also do the job, but I like the sharp edges the UHF array
produces.

Dick

----- Original Message -----
From: <jpero_at_sympatico.ca>
To: <classiccmp_at_classiccmp.org>
Sent: Sunday, June 10, 2001 3:38 PM
Subject: sync on green to horizontal and vertical wiring seperator.


> Hi!
>
> This is getting frustrating.
>
> This is fairly on topic because I run older Macs (1987 to 1991, and
> many nubus video cards) that does not have native separate syncs by
> design. I'm using a very dim Mac high resolution monitor. If
> adjusted brighter, it will lose sharpness. It's already adjusted
> perfectly and this doesn't helped. That's bad tube, caps that I can
> check with my ESR are replaced already.
>
> This is killing my eyes staring at that dim monitor bought about this
> thinking to solve that problem because finding decent monitors with
> sync on green and composite features that does have good tube is
> getting harder to find. I do have a semi-working Nec 3D but tube is
> real small! And at other extreme, I have 20" Nec monitor but I'm not
> gonna drag that thing here. HUGE and power hungry.
>
> Except I have this dead 17" with all this features is IDEK Liyama
> waiting for schematic but that will be long awhile till I have money.
> The important details I need is fusiable resistors, they blew and
> cooked off the numbers completely.
>
> But I might have one or two monitors I might able to extract certain
> IC to split the sync out to drive a peecee monitors which are in
> plenty around here.
>
> Otherwise if there a way to build that thing from scratch is nice.
>
> Cheers,
>
> Wizard
>
>
Received on Mon Jun 11 2001 - 04:20:14 BST