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7934 - failing storage tube?

 

P { margin-bottom: 0.21cm; }I recently was given a 7934 minusplugins as 'spares or repair' and was surprised to find that innon-storage mode everything that I have tried so far works perfectlyand the bandwidth and triggering seems fine. The trace is sharp, but a bitfaint on the fastest speeds (about 10kHz rep rate from an avalanchepulse generator) but fine with the room lights dimmed.
I have to admit to never having used astorage oscilloscope! We had the Tektronix 611 storage display unitattached to a mini-computer before raster graphics displays wereaffordable (colleagues at NASA Goddard had a colour graphics displaythat cost $250k) and later I used the Tektronix 4010 computergraphics terminals quite often so I am used to some of the artifactsthat you get with storage displays.
My question is whether my 7934 just hasan aging CRT or may need some adjustment on the voltage settingsaround the storage control. Currently the 'level' control on thetop right of the panel has its spindle broken and I cannot adjust it,a replacement is on order but will probably not arrive for a week ortwo. I don't claim to have made any exhaustive checks of the storageoptions (largely since I don't know what to expect!) but in generalterms I have a rather bright uniform background in storage mode. Some combinations of settings will darken the background but notuniformly (darker centre, bright edge) and the trace and readout arereasonably sharp against the brighter background but become blurredon the settings with better contrast. Save and erase do what youwould expect given the bright background.
So basically, if the tube is on the wayout then I will give the 7934 a wash and brush up and concentrate ongetting my 7904 100% right instead of the 99% at present. On theother hand if there is the prospect of improving the storageperformance with a bit of work then I can start reading and learningabout storage tubes and do a check on voltage levels while waitingfor the replacement pot to arrive.
Also a Merry Christmas to everyone,
Roger
 

On 12/19/2014 5:38 AM, Roger Evans very_fuzzy_logic@...
[TekScopes] wrote:

P { margin-bottom: 0.21cm; }I recently was given a 7934 minusplugins
as 'spares or repair' and was surprised to find that innon-storage
mode everything that I have tried so far works perfectlyand the
bandwidth and triggering seems fine. The trace is sharp, but a
bitfaint on the fastest speeds (about 10kHz rep rate from an
avalanchepulse generator) but fine with the room lights dimmed.
I have to admit to never having used astorage oscilloscope! We had the
Tektronix 611 storage display unitattached to a mini-computer before
raster graphics displays wereaffordable (colleagues at NASA Goddard
had a colour graphics displaythat cost $250k) and later I used the
Tektronix 4010 computergraphics terminals quite often so I am used to
some of the artifactsthat you get with storage displays.
My question is whether my 7934 just hasan aging CRT or may need some
adjustment on the voltage settingsaround the storage control.
Currently the 'level' control on thetop right of the panel has its
spindle broken and I cannot adjust it,a replacement is on order but
will probably not arrive for a week ortwo. I don't claim to have made
any exhaustive checks of the storageoptions (largely since I don't
know what to expect!) but in generalterms I have a rather bright
uniform background in storage mode. Some combinations of settings will
darken the background but notuniformly (darker centre, bright edge)
and the trace and readout arereasonably sharp against the brighter
background but become blurredon the settings with better contrast.
Save and erase do what youwould expect given the bright background.
So basically, if the tube is on the wayout then I will give the 7934 a
wash and brush up and concentrate ongetting my 7904 100% right instead
of the 99% at present. On theother hand if there is the prospect of
improving the storageperformance with a bit of work then I can start
reading and learningabout storage tubes and do a check on voltage
levels while waitingfor the replacement pot to arrive.
Also a Merry Christmas to everyone,
Roger

[Non-text portions of this message have been removed]
Practice, study, rinse & repeat, and ( only ) then maybe tweak some
internal adjustments.
I have two 7623A scopes and at one time used the storage extensively,
mainly for the setup and design of servo systems on large machine tools.
That was then and now I hardly ever use the storage on these scopes.
My 2232s/2432 scopes are just much better at it and the "playback" can
be adjusted for
the best capture on my phone camera.

The exception to the above is a few cases where the "variable
persistence" mode can be just the ticket.
You might just check the archives for more information.




[Non-text portions of this message have been removed]
 

Here's what I reported about my experience with a 7613 a while back, from message #95110:

"I also managed to get the controls loosened up enough to function. Unfortunately though, it looks like this unit has a lot of rough miles on it - the mesh or phosphor has permanent burns of old waveforms and readouts, leaving gaps everywhere that won't overwrite without intensity high enough to defocus and start blooming. It works OK in non-storage mode, but it's not a very good display for a regular scope. Since it would still need a lot of work just to get it all working, it will likely be relegated to the parts carcass department."

Mine was a pretty extreme case where the screen was so bad it didn't work well in any mode.

If your 7934 presents a decent picture in non-storage mode, then you can still at least use it as a regular scope, equivalent to the 7904, and it can serve as a parts donor to your 7904 (a lot of parts in common) if it ever becomes necessary. The display will never be as clear as that on a regular scope CRT, but may be good enough. I wouldn't worry about it seeming fairly dim with the low rep-rate fast pulse test - that's to be expected. Try it with a high frequency CW signal from a generator - it should be plenty bright then.

If tweaking up the storage system gets it working, then so much the better.

Ed
 

The 7934 is only closely related to the 7904A. They use mostly the same major
integrated circuits including the channel switches and vertical CRT amplifiers.

The 7904 is closely related to the 7834, 7844, and 7854.

On 19 Dec 2014 07:14:39 -0800, you wrote:

If your 7934 presents a decent picture in non-storage mode, then you can still at least use it as a regular scope, equivalent to the 7904, and it can serve as a parts donor to your 7904 (a lot of parts in common) if it ever becomes necessary. The display will never be as clear as that on a regular scope CRT, but may be good enough. I wouldn't worry about it seeming fairly dim with the low rep-rate fast pulse test - that's to be expected. Try it with a high frequency CW signal from a generator - it should be plenty bright then.
 

On my 7834s I thought the CRT image was pretty good until I got my 7904 and 7854
but I was used to 100 MHz oscilloscopes like the 22xx series.

On 19 Dec 2014 07:14:39 -0800, you wrote:

If your 7934 presents a decent picture in non-storage mode, then you can still at least use it as a regular scope, equivalent to the 7904, and it can serve as a parts donor to your 7904 (a lot of parts in common) if it ever becomes necessary. The display will never be as clear as that on a regular scope CRT, but may be good enough. I wouldn't worry about it seeming fairly dim with the low rep-rate fast pulse test - that's to be expected. Try it with a high frequency CW signal from a generator - it should be plenty bright then.
 

On my 7834s, I found that doing the z-axis and storage calibrations made a
significant improvement in the storage CRT performance. While burn in is
visible in storage mode, it does not seem to have much effect.

On Fri, 19 Dec 2014 10:38:34 +0000 (UTC), you wrote:

My question is whether my 7934 just hasan aging CRT or may need some adjustment on the voltage settingsaround the storage control. Currently the 'level' control on thetop right of the panel has its spindle broken and I cannot adjust it,a replacement is on order but will probably not arrive for a week ortwo. I don't claim to have made any exhaustive checks of the storageoptions (largely since I don't know what to expect!) but in generalterms I have a rather bright uniform background in storage mode. Some combinations of settings will darken the background but notuniformly (darker centre, bright edge) and the trace and readout arereasonably sharp against the brighter background but become blurredon the settings with better contrast. Save and erase do what youwould expect given the bright background.
So basically, if the tube is on the wayout then I will give the 7934 a wash and brush up and concentrate ongetting my 7904 100% right instead of the 99% at present. On theother hand if there is the prospect of improving the storageperformance with a bit of work then I can start reading and learningabout storage tubes and do a check on voltage levels while waitingfor the replacement pot to arrive.
 

1. The 7934 CRT in non-storage mode is definitely not as bright as a 7904 CRT.

2. *Which* storage mode? They operate very differently.

3. Do you have the operator's manual? If so, read it carefully (even
though it's not as clear and detailed as it could be).

4. Nothing you say makes me think there's anything wrong with the 7934 CRT.
 

Roger,
If you decide to not to go forward with your 7934 and wish to put it aside,
please contact me, as I am looking for a parts donor.
Regards,
Karin Anne Johnson
karinann at tampabay dot rr dot com
 

Thanks for the helpful replies, I was very pleased that the replacement for the broken 'Level' control arrived today. Three working days, from Greece to the UK, and during the Christmas rush period is very impressive.


Everything is now a lot clearer, the 'variable persistence' and 'fast variable persistence' modes work fine, adjustment of the 'Level' control gives a good contrast display on a dark uniform background. The only caveat being that if you change persistence then you have to readjust the 'level' and the beam brightness for best results, I suspect this is normal behaviour. 'Save' works fine and the save intensity also works.


Bistable mode works after a fashion but I always get a bright background whatever settings I use. The trace is quite visible but I suspect something may be out of spec. 'Fast Bistable' mode is not usable, with the eye of faith you might convince yourself there is a trace on the screen but not useful.


So this now looks like a very nice scope, Karin Anne, I fear it is too good to be a parts donor and it is also the wrong side of the Atlantic! I think the variable persistence mode will be the most useful to me anyway, I want to play with the sampling plugins, I should get a 7S14 from an eBay seller as soon as he can find some bubble wrap and I have already read the threads about mercury battery replacement.


Should be a fun holiday period!
Craig Sawyers
 

=============
Bistable mode works after a fashion but I always get a bright background
whatever settings I use. The trace is quite visible but I suspect something
may be out of spec. 'Fast Bistable' mode is not usable, with the eye of
faith you might convince yourself there is a trace on the screen but not
useful.
=============

Your scope is just fine. Forget about bistable entirely - the contrast is
lousy, and the background always bright. Since the "first use" in the
manual is based on bistable mode, most scopes have got a trace burn on the
storage mesh as first time users desperately tried to get some trace
contrast by cranking up the brightness. Check the archives for this.

Just use the variable persistence and fast variable persistence modes and
you will be a happy bunny.

Craig
 

Roger:
Best of Luck to you. You've acquired a very nice scope.
I've got two of them here but one has HV problems.
Possibly soon to be fixed. If I get ambitious enough.
Best of Holidays greetings to you.

Karin

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