Bleak Pictue with RGB-2-SCART

If you want to ask questions about how the machine works, peculiar details, the differences between models, here it is !
How to program the oric hardware (VIA, FDC, ...) is also welcome.
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Joined: Tue Jan 14, 2014 8:57 pm

Bleak Pictue with RGB-2-SCART

Post by assen » Tue Jan 14, 2014 9:21 pm

Hi, everybody,

Back in late 80's I had a clone of Oric Atmos (known as Pravetz 8D) which I decided to revive few days ago. First thing I tried was connecting to an LCD TV (sorry, no cathode tube TVs around any more). The RF output works, but seems the time has taken its toll on the UFH parts and the picture is distorted and unstable. Next I decided to try the RGB output and my post is about it.

I soldered a RGB-to-SCART cable by connecting the R, G, B, Sync and Ground directly to the corresponding SCART pins. While the Oric boots, I get a clear white 4:3 rectangular picture on the screen (which is 16:9 itself). When the Oric is ready, I get a stable and clear picture, but very dark and bleak (dark grey background and a bit darker text). Adjusting the brightness/contrast of the TV does not help (as can be expected).

Since I get stable picture on the screen, I guess the TV is picking up the RGB signal form the SCART even though I'm not applying any voltage to pins 16/18 (both are left unconnected).

Next I decided to measure the voltage levels of the RGB output:
- R, G, B are all approx. +1.65 V compared to the Ground.
- Sync is approx. 3.5 V compared to the Ground.

Could any of these levels be too low/high? Being an analog input, could the RGB get 'saturated' at such levels? I have seen an adapter which is said to bring the levels of R/G/B signals to some 0.7V each.

Has anybody tried to measure the levels their Oric produces at the RGB output? Or any other ideas/considerations?


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