PJ's Hitech Soundline 32k control panel PV650, light controller

An ancient relic pulled off from a bar. This unit has been used to control the dimmers in the bar. Most likely the dimmers have been operated either with 0...10V voltage control or 4-20mA current loop. At the moment we have no idea how it works, if it works. By feeding in 10V through the terminal first LED lights up and only by pressing first button and another one, the second LED lights up. Upon releasing the second button the LED goes off as well.

Light controller panel based on 1x HCF4017BE counter/divider and 2x CD4049UBCN hex inverter buffers. The unit is produced on 1991 so, no info from the internet seems to be available.