Today I had a little time to carry on with diagnosing the internal trigger problem with the 1801A/1821A set, that the rack width 180A came with.
I went through part of the 1821A adjustment procedure for the main & delayed sweep using the external inputs, TP204 & TP404 were both found to be out of spec at 1.6V & -0.4V, they were adjusted to within 15mV of 0V using R238/R422. There was nothing wrong with trigger symmetry and I stopped at this point, as the other adjustments are not trigger related. Strange how the tests & adjustment procedure in the manual only use the external trigger inputs.
OK that leaves two more possibilities for the internal trigger problem, the internal trigger amplifier in the 1821A, or a lack of a sync signal from the 1801A vertical plug-in.
At this point I decided to swap the 1821A timebase for the known working 1824A timebase, that now also displayed the same lack of internal trigger.
Next weekend I will have to trace the signal through the sync amplifier board (A6) in the 1801A with another scope.
David