Re: TDS544A with strange display #photo-notice


Siggi
 

On Sun, Mar 7, 2021 at 4:02 PM durechenew via groups.io <durechenew=
yahoo.com@groups.io> wrote:

No, the blue trace is not compromised, but your observation is correct;
the scope is set to display vectors, not dots, therefore, from time to time
a vector might be missing because there was not enough time to capture the
needed points of start and end (that's a guess) - remember that at slow
scan speed the number of samples are fairly low and increase with scan
speed.
I beg to differ. Try to switch that particular signal to one of the other
channels, my $0.02 says the trace dropouts will follow the trace color.


Idea of oscillation came to my mind too but I had to abandon it. The blue
layer of shutter is ON for a certain amount of time while everything that
needs to be blue is displayed by CRT. So those vertical stripes on blue
must be on screen; no connection to shutter functionality, otherwise
everything that is on screen (including the trace) would be chopped. Plus
is doesn't explain why those stripes are waving - like a flag (each
horizontal line in that area has those oscillations occurring for a longer
or shorter period of time during the frame).
The length of the blue stripes clearly follows the amount of white content
on the previous line and/or the line with the stripe.


And it's not oscillation because those would not be synchronized with
vertical raster lines (if you take a closer look, the second vertical line
is perfectly aligned with one of those vertical stripes and so is every
second vertical line; that tells me that those blue lines are synchronized
with a clock, not random frequency.
Good point, I can't explain that.
I don't think there should be anything on the CRT board that follows the
dot clock... I also don't think there's anything on the CRT board that's
per color, other than on the LCD driver board.
I don't know exactly how the raster scan occurs on these screens, but I'd
suspect the full raster is scanned for each color, changing the LCD shutter
between a full frame scan. ... time passes ... It's rather interesting that
there are 12 lines from the LCD driver board to the LCD shutter. It would
be unnecessarily complex and awkward to have an LCD that matches the CRT's
dot pitch - what the hell is going on there? IDK - what is LCS_CLK - it's
brought out to the LCD shutter logic.

My scope has also that possibility to check the colors, but I didn't
discover any possibility to change anything (maybe different scopes with
the same basic design have that feature enabled).

Per the manual: https://download.tek.com/manual/070871001.pdf:
To bring up the Color menu:
1. Press DISPLAY to show the Display menu.
2. Press Settings in the main menu until you select Color from the pop-up
menu (see Figure 3-4)

Good luck,
Siggi

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