Quick update on the Thandar SC110, I have discovered that the sweep timebase is alive and working but is not reaching the CRT. The signal is getting as far as the internal / external switch and is being switched OK there, the time / div switch is altering the signal just as it should do.
Surely, the fact that the X shift control can move the dots left and right on the screen should mean that I can discount the CRT from the equation, meaning that I now have completely dismantle the unit in order to extract the controls and amplifier boards, which will also of course mean that I'll be unable to further the progress of where the signal is going to.