Re: A 2465 teaser...

Chuck Harris
 

I should have said: "pulses are "related" to the transitions
when the display takes over the screen... The actual transitions
of the beam are invisible... as they should be.

-Chuck Harris

Chuck Harris cfharris@... [TekScopes] wrote:

Hi Tom,

It looks just like what you would see if you had a fast
marker pulse, and you sped up the timebase. At slow
timebase settings, it is just a spike, at faster settings,
it is a fast rise, with a much, much slower decay.

The "hooks" are about 5us in duration. The risetime is
very fast, but the decay takes most of the 5us.

I believe that I am looking at two things. Probably issues
with the channel switch:

1) a glitch that is leaking through whenever the sweep starts
drawing CH1/CH2 on the screen.
2) a stream of display glitches that leak through whenever the
channel switch switches between CH1/CH2 and the CH5, the
display.

I have zero doubt that the random looking grassy pulses are
the transitions when the display takes over the beam from CH1/CH2.
They disappear when the display is turned off.

Everything is complicated by the display timing logic. The 2465
tries to avoid the "holes" in the traces that happen when the
display has to happen, so it has 4 or 5 different modes that
range from alternating display and trace, to random display
writing, to writing display full time. The display timing logic
makes these decisions based on how long it has been since it has
refreshed the display.

-Chuck Harris

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