I have a 1741A whose A-B mode doesn't quite work (but other modes seem all fine).
If I switch a 2 channel signal to A-B, the sweep disappears far off the right edge of CRT. While BEAM FIND is pressed, it swoops back in (and looks correct).
I haven't opened it up to diagnose it per service manual but I figured I'd shoot off a lazyweb question first, just in case anyone had seen something like that before. I've tried all possible POSITION settings and can't bring the trace in. (I think POSITION is operating properly in other modes.)
I should add the Chan A and Chan B signals are both between 0/9V.