Re: A 2465 teaser...

Chuck Harris

The 2465 is not a digital scope. It is analog, but has
a digital microprocessor controlling all of the circuitry.

On the 2465, hybrids handle much of the circuitry. In the
case of the readout, the channel selecting switch is a
hybrid that has 5 identical input channels. 1-4 are CH1
through CH4, CH5 is uniquely for the display input.

The CH5 display is always selected, but CH1 through CH4 can
be individually selected by VS1-VS4.

The Channel Switch hybrid is just a multiplexor. The blanking
signals don't go to the Channel Switch hybrid at all.

So, if it is blanking timing, it should affect all channels
equally, but it doesn't. I can see the ugly stuff in the
CH1 and CH2 slots, directly at the output of the Channel Switch.

The truth is out there...

-Chuck Harris

Harvey White madyn@... [TekScopes] wrote:

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

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

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


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