"N_Cook" wrote in
:

wrote in message
.
..
Hi,

I'm currently having trouble with my good-ol' HM1005. It has some
problems focusing correctly.
When it's cold, you first see nothing on the screen. Increasing
intensity results in an almost completely glowing screen, looking
like an EL-backlight. Leaving it on for some minutes shrinks the glow
more and more to a spot (in X/Y mode) or to a horizontal line (in
normal operating mode). Now it's possible to use that thing, but it's
not completely working correct.
On the left side of the line the beam is more intense. I've made a
photo of that, please have a look at
http://www.preamp.org/dinge/hm1005.jpg.
Using a time base of 50ns shows some kind of overshoot next to that
bright spot. The trace is moveable to X and Y as it should (I did
that on the photo, so the bright spot is not on the grid).

I'd appreciate any kind of help that can lead me to the source of
this strange behaviour.


Thanks in advance and with best regards from Germany,

Lasse


Did it gradually or suddenly go wrong?
If you feed in a known accurate ,say, 1V pk-pk 1KHz signal in, does it
give the correct screen indication of 1V, 1KHz with relevant settings
?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/





First,check all the power supplies.Voltage and ripple.

then determine if the sweep circuit is working,then check the unblanking
waveform and Z-axis amp.
you should be able to vary the amplitude of the unblanking pulse at the
output of the Z-axis amp,with the brightness control.(not the CRT bias pot)


--
Jim Yanik
jyanik
at
kua.net