Thanks Len. You're welcome.
I think my original problem is something to do with sweep generation / horizontal timing. Both CH1 and CH2 are affected the same..both short traces start and stop exactly the same time. I assume you're talking here about the effect in the normal mode, not the XY mode. Not sure what is the common points between CH1 and H amp....maybe this is symptomatic of being in XY mode....?
If this was hum or ripple I would expect to see some jitter at start and end of the trace but it is rock steady...it really seems like a timing issue. I disagree, see below.
No scope to borrow at the moment.....oh I am in NSW, Central Coast. That's about 1500 km too far north to borrow mine.
Ray