Hi.
I had another look at the scope and brought my old Scopex out of retirement to help assist with the problem. I've deduced that the amplitude of the ramp waveform is constant for all settings of the timebase. This ramp appears to remain constant in amplitude though the X amplifier stages again for all settings of the timebase control.
This oscilloscope also has digital storage capability and I noticed when in this mode the scope appears to be behaving normally so one would think the X amplifier stages should be OK. As I say, the fault was initially temperature dependent but is now permanent. It would seem likely to be a semiconductor fault.
I find the timebase circuit is quite difficult to understand, for my brain anyway.
The service information is available from here:
https://cdn.rohde-schwarz.com/hameg-...08_english.pdf
Any further suggestions will be most welcome.
Regards
Symon