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From: Michael A. Terrell on 7 Sep 2009 13:32

IZ8DWF wrote:
>
> Hello all,
>
> I hope this newsgroup is still alive, I see too much spam lately :(


That's because you're posting through Google, where the spam comes
from. Get a real NNTP news serve and you will see very little.


--
You can't have a sense of humor, if you have no sense!
From: frank on 7 Sep 2009 15:47
nesesu <neil_sutcliffe(a)telus.net> wrote:

>> with vertical inputs grounded I can move the horizontal sweep from the
>> bottom to the top of the CRT, however the track is perfectly
>> horizontal only on the half part of the CRT, when moving up it
>> develops an arc of circle near the right end of the sweep, the circle
>> become larger the more it goes up until it reach about the anode
>> connection where the track shows a couple of sinusoidal periods; going
>> further up the circular arc changes direction (track goes down instead
>> of up vertically) and behaves in a specular manner.
>> Now I don't know if there's something that needs tuning in the X or �Y
>> drivers,
>> unfortunately this scope requires specialized calibration plugins to
>> go through all calibration steps, so I won't be able to follow the
>> exact calibration procedure.
>> However it seems to me that this kind of fault could be due to a bad
>> CRT, I'm not sure the Y voltage on the plaques should be variable
>> during a bare horizontal sweep, but also I'm not a great expert of
>> scopes.
>> Any hint is welcome.

> On the 'no signal' trace distortion, check the position of the trace
> vertical position pot for centre of rotation and see if the trace is
> in approximately the centre of the screen [vertically]. It is possible
> that the DC balance of the vertical amplifier is way off centre due to
> misadjustment or a component failure in the vertical amplifier or
> failure of one of the V+ or V- supply lines into the amp. I have seen
> what I think you are describing if the trace is shifted off screen
> due to a large DC component on the measured signal and trying to bring
> it on screen with the vertical position control.

the vertical position control works as expected. The track is only
distorted in the vicinity of the right side and when it is positioned in
the upper half of the screen.

> The Telequipment 'scopes of that period [I have a D83] have very poor
> resistors. I eventually changed out all resistors in the power supply
> and several in the trigger circuits. The high value ones [10meg] in
> the feedback divider mostly went open circuit causing the EHT to
> skyrocket, and the metal film ones in the trigger circuits became very
> temperature sensitive and would drift like crazy. Otherwise a nice
> 60MHz 'scope. Still going strong.

Yes, this had 4 open resistors in the EHT board, one 10M, two 4M7 and
one 3M9. So this scope probably suffered for a long time from too high
EHT, I don't know wether this can damage the CRT and result in the very
localized track distortion I'm observing.
After replacing the EHT resistors and reconnecting everything it
developed a short in the 105V supply caused by two transistors in the Z
grid controller going short circuit. This fact still puzzles me, but I
measured the voltages on the two dead transistor's sockets and they look
very normal.
I checked already all resistors in the power supply board, in the EHT
board and in the Z driver board.
I'm in travel until the end of the week, so I won't be able to replace
the two blown transistors before next saturday and see what happens.
Thanks for all suggestions.

Frank IZ8DWF
From: Michael A. Terrell on 7 Sep 2009 18:48

frank wrote:
>
> Michael A. Terrell <mike.terrell(a)earthlink.net> wrote:
> >
> > That's because you're posting through Google, where the spam comes
> > from. Get a real NNTP news serve and you will see very little.
>
> ok, I did it and you're right (fortunately the old "tin" newsreader
> still exists).
> However is a bit a p.i.t.a. to remember (or find out) what news server
> to use whenever I change ISP (I travel lot).
>
> Best regards and sorry for the OT.


No problem. The more people we can get off of Google Groups the
better. Then you can use Nfilter to drop anything posted from Google,
and not see enough spam to worry about. :)


--
You can't have a sense of humor, if you have no sense!
From: Jorgen Lund-Nielsen on 10 Sep 2009 06:06

IZ8DWF wrote:

> Hello all,
>

-snip-

> Now I have a full scan track on the CRT, time base seems to work
> correctly and also track vertical position works, but I see a very
> strange effect on the track:
> with vertical inputs grounded I can move the horizontal sweep from the
> bottom to the top of the CRT, however the track is perfectly
> horizontal only on the half part of the CRT, when moving up it
> develops an arc of circle near the right end of the sweep, the circle
> become larger the more it goes up until it reach about the anode
> connection where the track shows a couple of sinusoidal periods;


> However it seems to me that this kind of fault could be due to a bad
> CRT,

The effect is independent of the sweep rate?
I would expect a hard mechanical hit has loosen or bended a deflection
plate,
that often shows such effects and they are then sweeptime independent.
If it depends on sweep speed there is a very little chance for ripple
on the supply to show some weird screens but that's normaly not position
sensitive.

Jorgen
dj0ud
From: frank on 10 Sep 2009 10:29
Jorgen Lund-Nielsen <jorgen.lund-nielsen(a)xyz123desy.de> wrote:
>
>
>> However it seems to me that this kind of fault could be due to a bad
>> CRT,
>
> The effect is independent of the sweep rate?

yes, totally independent of sweep rate. Track bending is always at the
same position and of the same entity.

> I would expect a hard mechanical hit has loosen or bended a deflection
> plate,
> that often shows such effects and they are then sweeptime independent.

That's also my guess, but as I said, I'm not at
all an expert of scopes and CRT.
Maybe not a deflection plate as for more than half screen the track
looks absolutely perfect? Could it be a problem caused by too high
EHT for a long time?

Thanks
Frank IZ8DWF
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