[RogerEvans]

When you said that the spot blinked at slow sweep speeds I had a slight worry since the spot should be unblanked for almost the whole time. Anyway it looks like the unblanking is the next thing to be investigated, It looks like the ZUP signal from the timebase is what controls unblanking in analogue mode and if I have the logic the right way round a positive pulse on ZUP will unblank the beam.

ZUP comes from the logic chip K501 and with moderately slow speed speeds the beam should be unblanked nearly all the time. Check that the signals on either side of R503 and on pin 5 (Q) of K501 are all about the same and switch between a low of less than 0.5V and a high of at least 2.5V. Pin 6 (Q bar) of K501 should be the same signal but in the opposite phase. If pin 5 spends most of its time low then either K501 has failed or it is being reset too soon by the CLR input on pin 1. You probably need to use the dual trace feature on the Scopex to look at pin 5 and pin 1 at the same time - triggering on the pin 5 trace only.

Understanding the working of the end-of-sweep logic (that should reset pin 5 of K501) is beyond me at the moment but there is a 'sweep length' adjustment VR501 that you might twiddle to see if it has a bad contact and also try the different Ch1, Ch2, alt, chop options since that seems to enter into some of the unblanking circuitry.

Roger