Date   : Fri, 24 Mar 2006 21:40:38 -0000
From   : "David Hunt" <dm.hunt@...>
Subject: Re: BBC to 1084 revisited

> After I searched the Internet, among many other documents I found
> one how to connect the RGB signal to Philips 8833/Commodore 1084,
> the variant with a 8-pin DIN for the TTL signal.
> 
> I have a 1084S with the DB9 connector, and found pinouts so I made
> my own cable. However, it does not work properly:
> 
> 1. I connected the composite sync signal to horizontal sync input,
>     exactly like the 8-pin layout. The monitor syncs perfectly fine
>     on this input, leaving vertical sync unconnected.
> 
> 2. I connected intensity to 0V (ground) on the DB9 side. Maybe I
>     should've tried to connect 5V to it instead?
> 
> 3. The picture displayed is all red and black, not even shades of
>     red.
> 
> 4. After a short while, the picture starts to fade, gets blurry and
>     soon disappears completely. If I turn off the monitor, wait a
>     while and turn it back on again, I get the red on black.
> 
> I have checked all pins with a multimeter to ensure connection all
> the way at the same time no accidental shorts.
> 
> The cable I used was an old C2N (Commodore tape recorder) cable,
> which has a thick wire of shield running inside the cable. This
> shield is not connected on either side though. Each wire also has
> small ferrit (?) rings to prevent distortion - on both sides of
> the cable.
> 
> The 1084 monitor has once broken down and the power circuit was
> repaired. After that, the CVBS circuit doesn't sync on bright
> border colours - perhaps a wrong value on the component somewhere
> in the power circuit.
> 
> Does anyone know what could be cause of my problems? I'm suspecting
> a bad power circuit in the monitor, but analog RGB from my Amiga
> works perfectly fine. I don't have another 1084 or similar monitor
> to compare with. It could of course be a problem within the BBC.
> Maybe I should try to fix me a SCART cable (of which there are a
> few designs on the Internet) to see if it works properly with a TV.

Commodore 1084 9pin connector

Pin    Name            Analog Mode     Digital Mode
1      GND             Ground          Ground
2      GND             Ground          Ground
3      R               Red                     Red
4      G               Green           Green
5      B               Blue                    Blue
6      I               n/c                     Intensity
7      CSYNS   Composite Sync  n/c
8      HSYNC   n/c                     Horizontal Sync
9      VSYNC   n/c                     Vertical Sync

It looks to me as if there are no separate syncs available in TTL RGB on
your Commodore monitor. It is a simple matter to connect up to the analogue
RGB instead, a couple of small signal diodes in series with the RGB+SYNC
signals to bring the TTL voltage down to something more appetizing to the
monitor. Other than that you'd either need to make up a sync splitter or
hack about with the innards of the Beeb to get the signals you require.

Dave ;)