sck0006 wrote in
:

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 ide
a
what caused this? *

Probably got dropped;portables often suffer that.
Field Techs would sit the scope on it's rear end,and then
accidentally yan
k
on the probe cable,and the scope would fall forward,WHACK,and
sometimes th
e
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?

some CRTs didn't have anode voltages,just large cathode voltages,and maybe
+100 volts on the mesh lens or final gun element.
A Sign of a low budget scope....

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.

How do time marks look on the display?
or any fast-rise leading edge,displayed at 1 edge/major div.
Set the vertical to display the signal on the entire graticule,top to
bottom. Is everything straight?


Thanks,
Steve


I hope you mean 2 MINOR div. ;-)

It's a shame you can't buy a decent analog scope from TEK anymore.
They really have trashed what used to be a great company.

--
Jim Yanik
jyanik
at
kua.net