Date   : Fri, 24 Mar 2006 21:43:27 +0100
From   : Anders Carlsson <anders.carlsson@...>
Subject: BBC to 1084 revisited

Hello.

I am new to this list, after have acquired a BBC Master Compact a
few months ago. It came with a RGB cable, but of course I don't
have the original monitor where it fits. So far I've used the
monochrome composite output, and it works fine but no colour.

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.

Regards

-- 
Anders Carlsson, Sweden