hp46 with strange modification

[Roland57]

Today I got a hp46 in good working condition. Obviously someone has changed the SIN and the COS key in a very professional manner (see pictures).

   

On the back of the calculator a centronix-port has been installed.

   

Inside the calculator a professional-looking PCB has been installed back to the keyboard. The flat band cable from the main PCB to the display is routed through this new PCB, which looks very professionally made. Unfortunately there is no visible label or any indication to the manufacturer.

   

   

The START X/S key (former SIN) shows a cyclic behaviour: it either stores the x-register into REG 4, into REG 3, into REG 9 or clears the x-register. Function of KORR (former COS) is unclear. I assume this modification allows for data transfer via the centronix-port.

Because this mod looks very professional I assume it has been made more than once: does anyone have more information about this modification ?

Roland