Sync on Green RGB video

Marco Rauhut marco at
Sun Nov 19 03:32:23 CST 2017

I have the same problem with a cheap 19" LCD VGA Screen. What i made is 
to seperate the required sync signal with an LM1881 Video Sync 
Seperator. I used the standard application from the TI datasheet.The 
only difference is that i used an viariable resistor on pin 6 to adjust 
to the Sync Frequency. That is running with my Vax Station 4000 / 60.

Marco Rauhut

Am 19.11.2017 um 04:57 schrieb Douglas Taylor via cctech:
> On 11/18/2017 6:44 PM, william degnan wrote:
>> On Nov 18, 2017 4:09 PM, "Douglas Taylor via cctech" 
>> <cctech at <mailto:cctech at>> wrote:
>> >
>> > I have a couple of vaxes that output 'unique' video, Alpha 3000 
>> 300, Alpha 3000 400, Vax 4000 VLC, and Vax Station 3100 M76.
>> >
>> > The Alpha and VLC each have a 3W3 type of connector and the 3100 
>> has a 15 pin DEC designed connector.
>> >
>> > What does it take to connect these to inexpensive, modern VGA light 
>> weight monitors?
>> >
>> > Doug
>> >
>> I have played around with that problem.  If you have a converter to 
>> get into a VGA port a newer high-end vga display will be able to 
>> adjust, but not a cheap one.  Because I use my vice vga/digital 
>> display for mode stuff, I use a huge SGI color display for all of my 
>> 3w3 outputting systems and I just switch the cable around.  If you 
>> could imagine 5 or 6 systems clustered around the one display.
>> I am sure someone here has a technical explanation, but in a nutshell 
>> the 3W3 world signal isn't the same as a standard vga and cheap vga 
>> displays can't handle the refresh rate.  Someone will prob. refine my 
>> answer but that's why you can't just stick an adapter on there.
>> Bill Degnan
>> twitter: billdeg
>> <>
> I ran into a similar comment somewhere on the internet somewhere (it's 
> a big place) that you had to make sure that the LCD monitor supported 
> the H,V rates put out by the DEC video frame buffer.

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