On Jan 28, 11:43*am, Jim Yanik wrote:
sck0006 wrote in news:5df1d999-e9fe-43cb-84ba-
:

On Jan 28, 8:59*am, sck0006 wrote:
We have a 2205 with geometry problems on the crt. *It has fairly
severe trapezoiding ,the spacing at the top is narrower than that at
the bottom, appx .4div narrow at top, .2 div wide at bottom. *Any idea
what caused this? *

Probably got dropped;portables often suffer that.
Field Techs would sit the scope on it's rear end,and then accidentally yank
on the probe cable,and the scope would fall forward,WHACK,and sometimes the
CRT would be damaged,sometimes break completely.(I've seen CRT necks
snapped off)

We tried degaussing the screen, absolutely no
effect. *I inspected the tube for visible damage inside, nothing
sticks out as obvious. *The horizontal deflection is fine, the trace
is inline with the graticules across the screen within less than .
1div. *Any ideas how to fix this?

Thanks,

Steve

I forgot to add, adjusting geometry doesn't help.

Thanks,
Steve

it sounds like a misaligned deflection plate,as the horizonal gain varies
significantly from top to bottom.
Nothing you can do except get a new CRT.

BTW,I have pulled CRTs,and I could tilt the tube and hear bits of glass
from cracked electron gun rods tinkling as they slid around inside.
Just looking at the gun,the breaks were not always visible.Sometimes,the
particles would stick to the phosphor and create a dark or bright spot,or
damage the mesh lens and create linear distortions in small areas.

Also,TEK only spec'd the center part of the graticule,the outermost
division both H and V were looser specs,considered to not be part of the
measurement area.

Was that 2205 a TEK ceramic bell CRT? Or some foreign tube?
IIRC,the 2205 was from an Asian manufacturer.

--
Jim Yanik
jyanik
at
kua.net

Looks like it's ceramic.
Also, how does this tube work? There isn't an anode lead on it. Does
it get the HV from the rear of the tube, or is it a different type?

Fortunately, it is in tolerance at the center of the screen, and
approximately equally out of tolerance at top and bottom, so really,
it's just at ±2 div tolerance overall.

Thanks,
Steve