Tek 7T11A issues


I'm a new member, but have been an avid Tek scope user/collector/fixer ever since my extensive time using them as a former, now retired Bell Labs engineer.
But my ability to fix has recently been challenged with some problems in my 7S11/7T11A pair:

The 7T11A and 7S11 are situated in my 7904A scope, and the problem I am having with it is that I can’t get a stable trace. In fact, (and I think it is all set up correctly) with a square wave input (from my PG503) I get either a splatter of dots on two lines representing the top and bottom of the signal, but not triggering on a transition, or in some settings just a splatter of dots on the screen. And in some settings, from 50uS on down - non real time, you see nothing at all.

Any suggestions on how to proceed with diagnosis/repair would be appreciated.

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