7B70 gone bad...

john graves <jgraves2@...>

I've followed this group for quite a while: what an incredible wealth of knowledge the contributors have! Following this has been very educational for me.
I now have my first request for help:
Recently I purchased three 7B70 timebases on E-bay. The best one of the group had been working perfectly until recently, but it suddenly went bad.
The symptom is that it will only sweep once, then the trace freezes on the rightmost of the CRT. Any vertical excursions still occur, but the trace just sits there.
This happens on any triggering mode setting.
I do not have a manual for this timebase, but since I have two others that more-or-less work, I think that I could swap out the defective component.
I just need some better idea of which component may be defective.
If someone could suggest which reference designation would lead me to a likely bad part, then I'll un-plug and plug away.
Thanks so much for any help!
---John Graves


John, with no manual, it's difficult. Since intermittents are a big
problem with Tek products having socketed component, the first thing
I'd do is rock every transistor around in its socket. Better yet,
pluck the transistor out and push it back in a couple of times. Do
the same with the TDs and any ICs. That may clear the problem up.