I just got a 3405A and for test started working on a defective linear power supply.
After the rectifier on the big capacitor is a 100 Hz AC wave signal, which in fact has a 50Hz period.
Seems one diode in the rectifier is bad, so the wave form on every 2nd 100Hz half wave is instable.
How can I trigger on every 2nd slope? I need a timing condition, voltage levels are no help.
My old HAMEG has a simple feature called "trigger hold off", which disables a trigger for a certain time after first event,
that gives very easy a clean view.