I just tried removing C73 (33pF) and it made a remarkable difference to bandwidth on the 0.5v range of ch.A I am now getting -3dB sinewave response to 10MHz. I then used a good quality scope to check the squarewave response at U6, AIN and there was slight overshoot but no instability or ringing.
I have noticed that my DSO Quad will not trigger on timebase ranges of 0.2uS and 0.1uS when set for channel A only (ie. with all other channels in HIDE) Has anyone else seen this?