How can I manually set the CTS line on a PK2100 RJ12 connector?

I have a PK2130 (12v) which does not respond to Dynamic C. The PC (USB Com4) serial connection is OK - I can reach other z180 boards.

I have checked the DB9 - RJ12 cable and have replaced the DS1488B chip (with an MC1489P).

My serial line breakout box shows the CTS line is never set as it is with other Z180 boards.

A link to the schematics for the PK2100 (Pk2130) would be very helpful.

I anyone has other suggestions, they would be greatly appreciated.