Hi,
Dave
When you turn on the scop, where do you see the trigger trigger label on channel A or B, do they move up / down from the MOVE buttons of each channel? Keep in mind that with the MOVE button I can move beam A and / or B together with the TRIG mark down, completely out of sight.
Can you switch this label with the F1 button from the channel to the channel or to the EXTernal state?
How does the TRIG label appear when switching to a Ch-A that has no line at all?
And, if Ch-A is disabled, TRIG must display in EXTernal state.
Let's deal with button operations first.
I have a coordinating proposal here:
Measure the voltage between GND Ch-A and GNG Ch-B. Probably there will be noise from the operation of pulse converters of both channels.
I am bringing you to temporarily unite the GND of the galvanically isolated A&B channels. If you are confident in your actions, then do it.
Further.
Make a jumper from the 2-pin optocoupler H1320 (active Ch-B) to the 2-pin optocoupler H1120 (Ch-A).
In fact, we use working channel B to check the entire subsequent path of S-ASIC, D-ASIC, and so on to get the line (trace) image of Ch-A. If you are not confident in yourself, do not apply any voltage to the input of the channels, use only the AC background by hand.
Vladimir.