XEGS SECAM - 2 Color Knobs?

[abbotkinneydude]

Hello everyone,

 

I looked at the ATARI FAQ online but couldn't find a satisfying answer.

 

Would anyone know why the SECAM XEGS made for the French market has 2 color knobs?

 

Is there a way to adjust those in a standardized manner or is it just about finding the best PQ on your screen?

 

I'm attaching a picture of the MB (gorgeously restored by the tremendous Paul Westphal @ EightBitFix).

 

Thanks!

Edited October 27, 2018 by abbotkinneydude

[abbotkinneydude]

The SECAM 800XLF also includes 2 pots. 1 for horizontal, 1 for vertical?

 

Edited October 27, 2018 by abbotkinneydude

[Rybags]

Likely because of the way SECAM works - PAL and NTSC added colour to the standard by encoding it as a single signal where the phase offset determines what colour should be displayed.

SECAM does colour by transmitting the Red-Y and Blue-Y components on alternating scanlines. So it's likely that each pot alters one of those components.

 

There's a technical doc around (FGTIA.PDF) which describes the functionality of the Secam GTIA (which is used with a normal PAL Antic).

 

There's pins DICA and LOCK, C_VC and C_RF which are used in colour generation and aren't present on other systems. I suspect they are used in select logic to determine which component (and trimpot) is active per scanline. Also, the FGTIA outputs colour as a digital signal on 3 pins.

Edited October 27, 2018 by Rybags