On Thu, 22 Aug 2019 10:31:05 -0700,
et...@whidbey.com wrote:
>>>>>So I built a kit that uses an electrostatic deflection CRT for the
>>>>>display. It all turned out very well except the display is much more
>>>>>in focus on one side of the screen.
(...)
>I'll need to see if I can get thing to make just a straight line.
>If not I can lock the display to just showing digits. Then I can
>adjust the astigmatism and see if the digits on the right hand side of
>the display get sharper.
Is the scope really a kit? How old? I've had a bit too much
entertainment value from old carbon composition resistors that absorb
moisture and change value. It might be worth checking the resistance
of some of the resistors in the focus/astigmatism circuit. For
example, here's something similar caused by an open 332K resistor:
<
https://cromwell-intl.com/radio/tek2445a.html>
This is going to be difficult without a schematic. If you run out of
options, perhaps tracing the focus/astigmatism circuit, measuring
voltages, and scribbling a schematic might be useful.
>I can also swap the X axis wires, which mirror images the display.
>I know because I already did this accidently. If the focus problem
>mirrors too then I wonder what that would mean.
I don't know for sure, but your logic seems sound. If the astigmatism
problem remains the same, then the problem might be in the tube. If
it changes when the X deflection leads are reversed, it's in the
circuitry.
>I'll try the astig. adjustment first later today.
I've been trying to find a reasonable explanation of how the focus and
astigmatism adjustments function. As near as I guess from what little
I've found, the astigmatism adjustment compensates for axial symmetry
errors in the electron gun. That brings up the possibility that the
CRT might be sufficiently unsymmetrical to not allow astigmatism
correction, or that the circuit or parts are so screwed up so as to
not provide sufficient adjustment range.
From the TEK 5440 manual:
To check for proper setting of the Astig control, slowly turn
the FOCUS control through the optimum setting with a signal
displayed on the CRT screen. If the Astig control is correctly
set, the vertical and horizontal portions of the trace will
come into sharpest focus at the same position of the FOCUS
control.
...front-panel FOCUS and internal astigmatism controls have
been incorporated for arriving at an optimum CRT display.
FOCUS control R440 provides the correct voltage for the second
anode in the CRT. Proper voltage for the third anode is
obtained by adjusting Astig control R370. In order to
obtain optimum spot size and shape, both the FOCUS and Astig
controls are adjusted to provide the proper electrostatic
lens configuration in the CRT.
So, how does the vertical astigmatism look? As bad as the horizontal
or different?
Not much help, but maybe it will offer some clues.
--
Jeff Liebermann
je...@cruzio.com
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS
831-336-2558