Do they all do this?


steve@...
 

Hello All,

I'm not sure if my scope is construed as a classic and, therefore, if
I've posted this to the wrong group I apologize.

Anyway, I recently purchase a 7623A mainframe along with 7L12, 7A26
and 7B53A plugins. These all work fine and I'm jolly impressed with
the scope given that standard of kit I've used in the past.

I do have 3 questions, though:-

1. I was getting "dot crawl" on the trace, which was especially
apparent on the 2m/s horizontal setting (even with no vertical
plugins fitted). Switching OSD update function from interrupt drive
to end-of-trace removed this problem. I presume this is a "feature"
and, hence, the reason for the switch?

2. Sometimes the mainframe cuts out with a crack - only to return
again. I only noticed this happening since fitting the 7A26+7B53
plugins (left socket isn't used with just 7L12). I'm guessing it's a
problem in the HT circuit? Is there a favourite candidate for this
problem?

3. Using the storage facility in variable persistence works
fine using both normal/fast modes. However, when using bistable
storage the background is very bright and ,hence, there is very
little contrast between the background and the sample. I've adjusted
both the controls detailed in the service manual to no effect.

Thanks for any answers you may have,

Steve.


dhuster@...
 

1. I was getting "dot crawl" on the trace
I'm not sure what you mean by "dot crawl". Are you referring to the
mesh ghosting?

2. Sometimes the mainframe cuts out with a crack - only to return
again.
THAT doesn't sound good!

3. Using the storage facility in variable persistence works
fine using both normal/fast modes. However, when using bistable
storage the background is very bright and ,hence, there is very
little contrast between the background and the sample. I've
adjusted
both the controls detailed in the service manual to no effect.

Steve, the bistable mode on the variable-persistance scopes (7623,
7633, 7834, 464 and 466) aren't at all like the bi-stable storage you
may be used to with the 564B, T912, 314, 214 and 434 or the 4000-
series graphics terminals and 4051/52 desktop computers. You will
have a bright background and lousy -- REALLY lousy -- contrast. I've
never found a reason to use the bistable mode vs. the variable
persistance or high-speed modes on those scopes.

Dean


steve@...
 

--- In TekScopes@y..., dhuster@p... wrote:

1. I was getting "dot crawl" on the trace
I'm not sure what you mean by "dot crawl". Are you referring to
the mesh ghosting?
No, given it goes away when I switch end of scan updates for the OSD
on I imagine it's just the gun moving to update the OSD and, thus,
causing a brief break in the waveform trace.

2. Sometimes the mainframe cuts out with a crack - only to return
again.
THAT doesn't sound good!
No - I know have a service manual and will stripdown the HT section.
I'm guessing it's a dry joint on the line transformer.

3. Using the storage facility in variable persistence works
fine using both normal/fast modes. However, when using bistable
storage the background is very bright and ,hence, there is very
little contrast between the background and the sample. I've
adjusted
both the controls detailed in the service manual to no effect.

Steve, the bistable mode on the variable-persistance scopes (7623,
7633, 7834, 464 and 466) aren't at all like the bi-stable storage
you
may be used to with the 564B, T912, 314, 214 and 434 or the 4000-
series graphics terminals and 4051/52 desktop computers. You will
have a bright background and lousy -- REALLY lousy -- contrast.
I've
never found a reason to use the bistable mode vs. the variable
persistance or high-speed modes on those scopes.
Ahhh - thanks. Does sound more like a feature. It's almost perfect in
variable persistance mode - I just expected the same in bistable. The
service manual doesn't really outline the differences between the two
modes and how they physically function.

Overall it's a great piece of kit - I originally bought it with the
7L12 purely for spectrum analysis use - but the range of plugins (at
reasonable prices) just make it such a flexible piece of gear.

Thanks for your help,

Steve.


donlcramer@...
 

1. I was getting "dot crawl" on the trace
I'm not sure what you mean by "dot crawl". Are you referring to
the mesh ghosting?
No, given it goes away when I switch end of scan updates for the OSD
on I imagine it's just the gun moving to update the OSD and, thus,
causing a brief break in the waveform trace.

If you are seeing an intensitiy modulation of the trace and I think you're
correct in that the OSD update and the waveform you're viewing interact
resulting in a slow beat frequency which is visible to the eye. I've seen
this effect before many times in the last 12 years with my 2465A I use at
work. I just confirm it is the scope by turning off the readout, at which
point the effect goes away. My recollection is that it usually occurs while
in delayed sweep mode. Perhaps the resultant low duty factor sweep rate
reduces the number of available sweeps for the readout to be written and thus
there is more of a chance to see the readout update artifacts.

Rgds,

Don


Miroslav Pokorni <mpokorni@...>
 

Dean,

Isn't bistable mode supposed to give you longer storage time than variable
at longest time setting and I believe that what you store in bistable stays
there (on the half of screen ?) while you can get new sweep.


Regards

Miroslav Pokorni

-----Original Message-----
From: dhuster@pb.k12.mo.us [mailto:dhuster@pb.k12.mo.us]
Sent: Friday, August 31, 2001 6:11 PM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Do they all do this?


> 1. I was getting "dot crawl" on the trace

I'm not sure what you mean by "dot crawl". Are you
referring to the
mesh ghosting?

> 2. Sometimes the mainframe cuts out with a crack - only to
return
> again.

THAT doesn't sound good!

> 3. Using the storage facility in variable persistence
works
> fine using both normal/fast modes. However, when using
bistable
> storage the background is very bright and ,hence, there is
very
> little contrast between the background and the sample.
I've
adjusted
> both the controls detailed in the service manual to no
effect.


Steve, the bistable mode on the variable-persistance scopes
(7623,
7633, 7834, 464 and 466) aren't at all like the bi-stable
storage you
may be used to with the 564B, T912, 314, 214 and 434 or the
4000-
series graphics terminals and 4051/52 desktop computers.
You will
have a bright background and lousy -- REALLY lousy --
contrast. I've
never found a reason to use the bistable mode vs. the
variable
persistance or high-speed modes on those scopes.

Dean



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dhuster@...
 

Miroslav, I suppose that bistable vs. variable-persistance storage
times are arguable. But as I recall, there were techniques that
could be used to keep a v-p waveform stored for a very long time. On
the bistable storage scopes, the background would usually start to
slowly come up and kill contrast until the waveform was gone. And a
lot of that has to do with how you have the storage circuit
calibrated. There was always a stored writing speed vs. storage time
compromise.

I think that bistable storage was provided on many of the v-p
mainframes just because it could be. Afterall, you don't want the
company who invented bistable storage to not provide it if they can!

Dean


Miroslav Pokorni <mpokorni@...>
 

Dean,

At first I was to say that I am not aware of techniques to extend variable
storage to long term, but your mentioning of writing speed trade off made me
think again. To the best of my recollection, writing intensity has to be
adequate, i.e. not to low or you loose your image too soon, but more
important part is flood gun, i.e. viewing intensity, to be sparing; even
better, if you use flood gun only when you want to see image, storage time
can be considerably extended. If my memory serves me right, several times I
managed to keep images for few hours by turning off flood gun.

I think that bistable storage was provided on many of the
v-p mainframes just because it could be.
Boy, you are really coming down with both feet on that poor bistable
storage. You were with Tektronix and you would know that better, but I am
not so sure that Tektronix did first storage CRT. Back in 1969 I worked with
a Hughes storage scope. At the time, that scope was getting long in the
tooth, screen had burn marks and would easily bloom; I think that scope was
made in the first part of 60s. The place where I worked at the time had a
predilection for Tektronix and before my time had a large purse with loose
strings, so I doubt that they would have bought anything from anyone else
but Tektronix, only if it was available. There were times when I thought
that place would buy desks from Tektronix, if Tek would only sell desks. As
you might have guessed, I have been infected at the place; all these talk by
me about bad practices at Tektronix seem to be just to reassure myself that
my judgement is independent.


Regards

Miroslav Pokorni

-----Original Message-----
From: dhuster@pb.k12.mo.us [mailto:dhuster@pb.k12.mo.us]
Sent: Wednesday, September 05, 2001 9:44 AM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Do they all do this?

Miroslav, I suppose that bistable vs. variable-persistance
storage
times are arguable. But as I recall, there were techniques
that
could be used to keep a v-p waveform stored for a very long
time. On
the bistable storage scopes, the background would usually
start to
slowly come up and kill contrast until the waveform was
gone. And a
lot of that has to do with how you have the storage circuit
calibrated. There was always a stored writing speed vs.
storage time
compromise.

I think that bistable storage was provided on many of the
v-p
mainframes just because it could be. Afterall, you don't
want the
company who invented bistable storage to not provide it if
they can!

Dean



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dhuster@...
 

Miroslav,

No, no! I don't stomp on bistable storage with both feet. I just
don't like "bistable" storage on v-p scopes. I loved the bistable
storage of the 564B, 214, 314, 434, 577D2, etc. And the bistable
storage graphics terminals and computers were fine also.

I seem to remember that hp (they really developed v-p since Tek had a
lock on bistable) had a method of shutting down their scopes so that
the stored image was retained for a really long time and would be
there when you turned the scope back on. Is my memory slipping on
that issue?

Dean


Arnoud van der Wel <A.P.vanderWel@...>
 

I seem to remember that hp (they really developed v-p since Tek had a
lock on bistable) had a method of shutting down their scopes so that
the stored image was retained for a really long time and would be
there when you turned the scope back on. Is my memory slipping on
that issue?
You are right, I had a HP 18x (I think it was a 183..) with v-p storage and
in the manual it had a procedure for shutting down and turning on the scope
while retaining the stored waveform. The manual claimed storage for up to a
week. I only tried once for a day or so and that worked fine.

The tube was in really good shape, too. Maybe thanks to the HUGE warning
label stating that it was best for the tube if the scope wasn't used at all,
and if you *really* had to, please turn the intensity down as far as
possible and turn it off again as soon as possible... :)

Now if only I would have been able to find a power cord for that one......:)

Regards,

Arnoud van der Wel.


Miroslav Pokorni <mpokorni@...>
 

Dean,

I do not know about stored image surviving power cycling. If 1700 series hp
that I used had that feature I must have been too technical to read manual
and find out about that.

Now that I think of it, I realize that I really do not know how variable
persistence scope work. I will have to look that up because it seems to me
that I have been thinking of all storage scopes through perspective of a
bistable one.

Regards

Miroslav Pokorni

-----Original Message-----
From: dhuster@pb.k12.mo.us [mailto:dhuster@pb.k12.mo.us]
Sent: Thursday, September 06, 2001 5:53 AM
To: TekScopes@yahoogroups.com
Subject: [TekScopes] Re: Do they all do this?

Miroslav,

No, no! I don't stomp on bistable storage with both feet.
I just
don't like "bistable" storage on v-p scopes. I loved the
bistable
storage of the 564B, 214, 314, 434, 577D2, etc. And the
bistable
storage graphics terminals and computers were fine also.

I seem to remember that hp (they really developed v-p since
Tek had a
lock on bistable) had a method of shutting down their scopes
so that
the stored image was retained for a really long time and
would be
there when you turned the scope back on. Is my memory
slipping on
that issue?

Dean




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