Microvitec Cub Monitor & Homebrew computer

[Matthew]

I have made a basic computer that works perfectly with a standard PAL TV.
The video and sync go into a TV modulator and the result is very good.

I now want to output the display into an old Microvitec CUB monitor (as used
by the old BBC computers). This monitor is PAL and has TTL inputs for RGB
and CSYNC.

I am having trouble getting the sync to work properly. Am I right in
assuming that I *should* just be able to take the 'or'd hsync and vsync from
a TTL gate and put it straight into the CUB? I'm getting a very bad display,
although I can make out the characters on screen.
I have also tried inverting the 'or'd CSYNC to make it negative going but
that doesn't help either.

Any ideas??

Thanks,

Matthew

 

[Sprow]

I have made a basic computer that works perfectly with a standard PAL TV.
The video and sync go into a TV modulator and the result is very good.

I now want to output the display into an old Microvitec CUB monitor (as used
by the old BBC computers). This monitor is PAL and has TTL inputs for RGB
and CSYNC.

I am having trouble getting the sync to work properly. Am I right in
assuming that I *should* just be able to take the 'or'd hsync and vsync from
a TTL gate and put it straight into the CUB? I'm getting a very bad display,
although I can make out the characters on screen.

It's difficult to understand what you mean by "very bad display", is
it not locked in the V or H? Or something else?

I have also tried inverting the 'or'd CSYNC to make it negative going but
that doesn't help either.

The choice of OR/XOR/NOR/XNOR of course depends on the polarity of the
component syncs your SBC produces!

Any ideas??

Lots: line phase, C205 bypass, faulty monitor, amongst others,
Sprow.

 

[Matthew]

Problem solved now. It turned out to be the vsync wasn't synced to the
hsync. Vsync is now derived from the hsync pulses. It's strange, the
tv coped with it but the monitor didn't.