http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv020.cgi?read=210829
Just wanted to share that I've managed to fix this. The very small silver capacitor on the bottom right of the board had a lot of flux around the solder, similar to the display.
When I cleaned the solder near the display, there was no change, but after cleaning around this little capacitor - it works 100%. Over the moon now, I have a working CX and my original C working 100%. Now its time to do the gummy wheel on the card reader...