Re: A 2465 teaser...

Harvey White
 

On Fri, 10 Nov 2017 01:37:50 -0500, you wrote:

<snip>
An additional clue is the leading hook's decay curve changes
slope with sweep speed, but the scope will not trigger on
this signal, nor on any of the random grass that appears on
the trace. That indicates that it is getting injected after
the trigger pickoff.

I am pretty certain it has something to do with the display
readout logic.
I don't quite have that scope, but they have to do much the same in
the 7000 series for the readouts.

I think what you're seeing in the ___ |___ _____ are the switching
transients caused by inadequate blanking caused by the readout
generator.

The generator chops the beam, runs the readout, then puts the beam
back where it was. For that transition from trace to readout, the
beam is obviously blanked. If that blanking is messed up, then I
suspect you get the results you see. Won't be particularly sensitive
to sweep speed because it's a digital scope. I'd be looking at
inadequate leading edge sharpness on the chopping blanking pulses
myself.

Harvey



-Chuck Harris

edbreya@... [TekScopes] wrote:
You may want to check all readily accessible hardware mounting and grounding, particularly around the delay line. If the hooks are constant, then they must be leaking into the circuit past the front-end, and somehow localized so some parts are not affected. The one thing that is commonest to all sections and operations is the grounding. Check that all screws are tightened up snug (and that none are missing), and jiggle things around to see if the symptoms can be aggravated.

To see if you've got some kind of ground loops at the front, jump the apparently unaffected CH3 and CH4 inputs to the CH1 and CH2 - it's easy to just use BNC cables for this.

Ed

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