7A15A issue or limitation??



I have been playing around with my 7A15A's, in different 7603 Mainframes, and have a 'jittering' or 'flickering' of the 4V Calibration signal.
The 'jittering' is a movement, always to the left, of the trace along the horizontal axis and return to the correct position.

I can define this issue or limitation as follows:-
Independent of Mainframe - 2 x 7603's used
Independent of Timebases - 7B53 and 7B92A used
Only occurs in TRIG SOURCE/VERT MODE with VERT MODE/ALT - both traces are stable in all other Modes
Only one of the traces becomes unstable
Only occurs when traces from each Vert Amp are 'un-overlapped' - when the two traces are overlapped, both traces are stable

The Manual states that in TRIG SOURCE/VERT MODE .... "each sweep is triggered by the signal being displayed on the CRT"

This suggests to me that when I dive into the Circuit Descriptions, that I should be looking for some 'switching mechanism' which is swapping the Triggering mechanism between the signals from each Vert Amp.
If this 'switching mechanism' is faulty or receiving a weak signal, then this maybe causing poor triggering, hence the 'jittering'.
However, this 'switching' between Vert Amp signals would occur in the Timebase or Mainframe.
But that doesn't make sense because the 'jittering' occurs in both 7A15A's, independently (ie. 7A15A + 7A26 + 7B92A etc), and in 2 different Mainframes, and with different Timebases.
So .... where have I gone wrong here???? ..... or is this a limitation of the 7A15A???

Any guidance is appreciated.

Melbourne, Australia

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