HP 41CX Halfnut CX EXT FCN missing

[HPnerd]

Hi all, maybe you can bring light in my problem:

i changed the backplane pcb due corrosion and missing lanes at my HP 41CX 2652Sxxxxx.
The donor of the backplane was a working CV 2818Sxxxxx (without the CX-addon pcb).
After changing the backplane the calculator was a nice "CV", okay i soldered the CX-addon pcb, a TIME 2C and CX TIME was added - but no EXT FCN nor a CX EXT FNC!
The additional catalogs 4,5 and 6 are missing as well...

So i did a rework of the ROM at the main pcb - now everything execpt the main pcb (same partnumber) was "CX" - but still the same - no ECT FCN nor CX EXT FCN nor catalogs...

Where the hell is the CX EXT FCN located at the Halfnunts?

Thank you for your answers, best regards from Austria
Walter