Reading the user manual PDF which I linked, discloses this:
"The negative or transparency is metered (choice of integrated or spot readings) on the projection plane with the aid of a probe before the exposure. All further operational characteristics are described in section "C") Operating functions" on page 8 of this instruction manual."
and includes the the COLIDESK 1200 control unit, aka ECU1200 and spot/avering probe. outside of the AC1200 user manual, there is NO reference to the Colidesk 1200!
"However, in the case of an Q~iQmQii~ ~~hi[Q~ii~~ ~~~Q~~[~ 2~2i~mL the printing light's appropriate color contents in blue, green and red are obtained by time control. After triggerIng the exposure sequence, the exposure will be started with so-called white 1 ight, i.e. there are no printing filters in the light path. As soon as the requIred color contents In blue, green or red have been obtained the appropriate prlntlng filter (yellow, magenta, cyan) swings automatically and fully into the 1 ight path (4) and reflects the corresponding color content. The exposure with this color is thus finished.
The three printing filters will swing into the light path, either sequentially or simultaneously, depending upon the length of the required exposure time (5), (6). Once the third filter (yellow, magenta or cyan) swings into the light path, the exposure sequence IS finally over. On the Durst AC 1200, the printing filter's sequential sWInging-In phase is controlled automatically."
So the AC1200 appears to be a subtractive head (CYM filters) but the controller decides when to swing in/out filters, either sequentiall or simultaneously, to achieve the exposure of the paper. So inherenly the head is very different from every other dichroic color head in which filter values are dialed in and remain stationary until filter values are changed.
There is a listing a control unit AC1201 for the AC1201 on eBay, sold as-is
https://www.ebay.com/itm/3730065961...8H7ydzyvHko7En8P4J0IxBtmnqVOftbwaAn1VEALw_wcB