Sun Monitor (UK)

From: Richard Erlacher <>
Date: Mon Jul 19 22:02:06 1999

Now, hold on there, slim . . .

The GDM1950 that I had for a couple of years required negative-going sync.
The PC may not be generating negative-going sync, but you can bet it will
generate negative-going composite blanking! What's more, the GDM1950 I had
was complete with a switch which enable sync-on-green decoding, and it's
likely this one has it too. That provides an alternative to figuring out
how to switch the polarity of the sync the card puts out. I've never been
particularly good at that sort of thing, hence once built a little adapter
with XOR buffers, each of which could serve either as a buffer or as an
inverter, depending on how its "other" input was jumpered.

I'm also not convinced that the notion of "seeing something" as opposed to a
total lack of sync give much encouragement. If the polarity is wrong, for
example, it's likely even a monitor being driven at the right frequencies
will fail to sync. If only one of the sync signals is at the wrong
polarity, it might seem to sync, or not, and if only the vertical is right,
or only the horizontal is right, who knows what will be seen. The first
step, IMHO, is to examine and measure the signals. Since they're available
separately, It should be easy to count them.



-----Original Message-----
From: Tony Duell <>
To: Discussion re-collecting of classic computers
Date: Monday, July 19, 1999 7:02 PM
Subject: Re: Sun Monitor (UK)

>> a SuperMac rebadged 19" GDM1950 that I picked up from the curb. It has 5
>> connectors and displayed a dark screen when I powered it up bare, but I
>> encouraged because there was static on the screen. When I connected it
with the
>> 5 BNC connectors to the adaptor I use on my NEC multi-sync 4Ds and turned
it on
>> without a computer powered up, for one glorius moment it displayed an
>> screen which then turned "IBM-blue" and then either to jaggies or
>> recall which). Since then it only displays jaggies. I hesitate getting a
>> fixed-freq card for it since they are quite expensive and I'm not sure it
>> works. As well, I use the NEC as an all purpose display with DOS, Mac,
and PS2s
>> on a ABCD switchblock so it would only be a secondary unit.
>Most expensive/difficult to fix faults on monitors result in no display
>at all. The fact that yours is doing soemthing probably means it can be
>repaired - if it needs it. Most likely it just can't sync to the PC output.
>> What is the "application connector composite blanking signal" and where
>> I find it. Would the V-sync and H-sync BNCs be ignored ?
>You don't need to bother.
>Some monitors, particularly workstation ones, use 'sync on green'. There
>are 3 BNC connectors. Red and Blue are what you'd expect. But the green
>signal is really a composite video signal consisting of the 2 sync
>signals and the green part of the video.
>PCs don't do that. They have 5 separate signals - R, G, B and the 2
>To use sync-on-green monitors with normal PC video cards you have to
>combine the syncs with the green video signal. There are various ways of
>doing this - Richard's method is to pick up a signal off the VGA card
>'feature connector' (do those still exist???) and to resistively mix it
>with the green video signal. An external sync mixer is not that complex,
>But as your monitor already accepts separate syncs, you can just feed in
>the sync signals from the PC as you have been doing.
Received on Mon Jul 19 1999 - 22:02:06 BST

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