2430A Repair - a first in many ways


Joerg
 

Hi everyone, thanks for letting me join this group.

This is my first Tektronix Scope - and this is how I go it: after my trusted Hameg died, I obviously needed a replacement. I found a Tektronix 2340A one Ebay classifieds in the local neighbourhood of Regensburg in Bavaria/Germany that was "fully functional" at a reasonable price. Being somewhat of a dinosaur myself with my fully analog Hameg, I thought I treat myself to an archaeopteryx of sorts with this storage scope. Shortly before I set off to pick it up, the seller called and broke the news that even though it had definitely been fully functional when he had last used it a couple of years ago, it turned out it wasn't quite so when he turned it on this morning and if I was still interested..... Being a candid romantic and the guy being a young father I still bought the scope (no, not at the original price...) and now I have two broken scopes on my desk... Still, I think a made the right choice as you will certainly all agree ;-)

So I thought I share my progress trying to getting it back to working with you and since I'm new to Tektronix scopes, I'm happy to hear any advice you can give on how (not) to progress. I've documented my current progress in https://groups.io/g/TekScopes/album?id=263696

After initial turn on, the fan turns on, trigger LEDs blink, GPIB LEDs light up but don't cycle through a counting pattern. There is no trace on the screen and no menu items, but the screen is illuminated with a red glow
https://groups.io/g/TekScopes/photo/263696/3218886?p=Created,,,20,2,0,0

Taking it a apart, I was quite impressed with the build quality and the nice setup of hinged boards. I checked the DC voltages on the side panel to find the negative ones being off
https://groups.io/g/TekScopes/photo/263696/3218887?p=Created,,,20,2,0,0

Removing the top two boards, I checked the voltages on the power supply board and they were ok. Booting it up in this state did display a trace, i.e. a bright dot in the center of the screen, so the HV and the CRT Heaters are working, but no control over intensity.

So I suspect a short somewhere and put things back together again piece by piece. Finally, I can identify that removing jumper J100 from the top board brings back the trace. I find two shorted tantalum caps:
https://groups.io/g/TekScopes/photo/263696/3218888?p=Created,,,20,2,0,0
I have control over focus, astigmatism and trace rotation, but not intensity.

According to the schematic, these are 2.7uF Caps, but measuring the ones next to the broken ones, I measure 26uF, though... So I've ordered replacements for all four of these.

I've opted to replace them with 2.7uF 10% as in the original, but it seems that one could just as well replace 3.3uF 20% at 1/10th of the price here. They just stabilise +/-15V for a push pull. What are your thoughts on this?

Also, from you experience, what are other typical points of failure/fatigue in this particular model that I should check? There are more tantalum caps after all...

Thanks a lot for your help!


 

Welcome Jeorg! Yes, rescuing an old and in distress Tek scope is always the right choice!

One comment, and maybe the least helpful that you will receive, is that the "red glow" you saw when powering up the 2430A for the first time scale (or "graticule") illumination.

Another comment, possibly of more help: It looks like there is only a single "INTENSITY" control and that is multiplexed for the A and B traces, readout, and scale illumination functions (with the "SELECT" button just to the left of the INTENSITY knob). You may in fact have full control of all the screen intensities, but maybe you just had not selected the correct one, or maybe the SELECT button is dirty and not registering when you push it.

-- Jeff Dutky


Szabolcs Szigeti
 

Hi,

Congrats for the promising repair.
In my experience, you can expect the PSU caps to fail, actually I suggest
you check all the caps on the secondary side of the switching supply. They
can be leaking and still work. I don't like recapping without a good
reason, but I had to replace them on all of my three 2430A/2440 scopes.
Also in the PSU are the infamous RIFA caps and the power line filter.
Especially in the 230V world they can have a very stinky end.
For the intensity, this is not a real pot like focus or astigmatism, but
intensity is controlled indirectly by the CPU and you can select the
intensity of what you want to set, like trace, or readout.
An easy way to test all the pots and buttons that are CPU controlled is to
bring up the help screen and move the controls. Help should be displayed
for all the pot and switch you move.
I assume you have familiarized yourself with the service manual, but the
compulsory warning: use an external fan to cool the CCD module if you run
the scope out of its case for anything longer than a few seconds.
Once everything works, bsides doing the simple self cal and ext cal, I
suggest you go and do the adjustments to bring the scope in spec. It can
have a surprising amount of improvement as it is very much possible that
the screen geometry is not in its optimal state anymore. It may even be
possible that intensity problems are caused by drifted screen bias setting.
Also setting like the CCD clocks can have a great effect. Fortunately for
the 2430A it is not that mind and eye boggling task than for the 2440.

I know that not everyone is all that satisfied with these early Tek DSOs,
but I actually like this family of scopes, the 2440 is my go to scope
usually.

Szabolcs



Joerg <joerg.reichardt@gmail.com> ezt írta (időpont: 2021. máj. 4., K,
6:26):

Hi everyone, thanks for letting me join this group.

This is my first Tektronix Scope - and this is how I go it: after my
trusted Hameg died, I obviously needed a replacement. I found a Tektronix
2340A one Ebay classifieds in the local neighbourhood of Regensburg in
Bavaria/Germany that was "fully functional" at a reasonable price. Being
somewhat of a dinosaur myself with my fully analog Hameg, I thought I treat
myself to an archaeopteryx of sorts with this storage scope. Shortly
before I set off to pick it up, the seller called and broke the news that
even though it had definitely been fully functional when he had last used
it a couple of years ago, it turned out it wasn't quite so when he turned
it on this morning and if I was still interested..... Being a candid
romantic and the guy being a young father I still bought the scope (no, not
at the original price...) and now I have two broken scopes on my desk...
Still, I think a made the right choice as you will certainly all agree ;-)

So I thought I share my progress trying to getting it back to working with
you and since I'm new to Tektronix scopes, I'm happy to hear any advice you
can give on how (not) to progress. I've documented my current progress in
https://groups.io/g/TekScopes/album?id=263696

After initial turn on, the fan turns on, trigger LEDs blink, GPIB LEDs
light up but don't cycle through a counting pattern. There is no trace on
the screen and no menu items, but the screen is illuminated with a red glow
https://groups.io/g/TekScopes/photo/263696/3218886?p=Created,,,20,2,0,0

Taking it a apart, I was quite impressed with the build quality and the
nice setup of hinged boards. I checked the DC voltages on the side panel to
find the negative ones being off
https://groups.io/g/TekScopes/photo/263696/3218887?p=Created,,,20,2,0,0

Removing the top two boards, I checked the voltages on the power supply
board and they were ok. Booting it up in this state did display a trace,
i.e. a bright dot in the center of the screen, so the HV and the CRT
Heaters are working, but no control over intensity.

So I suspect a short somewhere and put things back together again piece by
piece. Finally, I can identify that removing jumper J100 from the top board
brings back the trace. I find two shorted tantalum caps:
https://groups.io/g/TekScopes/photo/263696/3218888?p=Created,,,20,2,0,0
I have control over focus, astigmatism and trace rotation, but not
intensity.

According to the schematic, these are 2.7uF Caps, but measuring the ones
next to the broken ones, I measure 26uF, though... So I've ordered
replacements for all four of these.

I've opted to replace them with 2.7uF 10% as in the original, but it seems
that one could just as well replace 3.3uF 20% at 1/10th of the price here.
They just stabilise +/-15V for a push pull. What are your thoughts on this?

Also, from you experience, what are other typical points of
failure/fatigue in this particular model that I should check? There are
more tantalum caps after all...

Thanks a lot for your help!










Joerg
 

Hi all,
thanks for all the feedback and ecouragement. I'm happy to report success: https://groups.io/g/TekScopes/album?id=263696&p=Created,,,20,2,0,0

It's almost been too easy.... I'll keep your input on recapping in mind but want to familiarize myself with the scope a bit more first. Also, I need to fix my Hameg so I can use it in further checks.

As you all will agree, two skopes are better than one!

One thing I did notice already: I can't seem to move the cursors and waveforms across the whole vertical range. Is this by design?


Cheers
Jörg


Michael W. Lynch
 

On Tue, May 4, 2021 at 02:59 PM, Joerg wrote:


One thing I did notice already: I can't seem to move the cursors and waveforms
across the whole vertical range. Is this by design?
Jorg,

Progress is a good thing. As far as this question above: The cursors will move all the way to the visible limits of the vertical and horizontal edges of the screen. The trace should be able to be positioned vertically, including off the visible screen. At least this is how my 2440 reacts.

--
Michael Lynch
Dardanelle, AR


Bert Haskins
 

On 5/4/2021 3:59 PM, Joerg wrote:
Hi all,
thanks for all the feedback and ecouragement. I'm happy to report success: https://groups.io/g/TekScopes/album?id=263696&p=Created,,,20,2,0,0

It's almost been too easy.... I'll keep your input on recapping in mind but want to familiarize myself with the scope a bit more first. Also, I need to fix my Hameg so I can use it in further checks.

As you all will agree, two skopes are better than one!

One thing I did notice already: I can't seem to move the cursors and waveforms across the whole vertical range. Is this by design?


Cheers
Jörg
I have a pristine 2430 and several other digital scopes.

When the 2430 has not been used for a while I often see diagnostic errors that will go away just by doing two or three power up shutdown cycles.

- Bert





Joerg
 

silly me, it is by design. I had just been too careful and had not previously experienced the spring loaded mechanism on the turning knobs.... I quite like it!


Pwrelectronics
 

The first digital scope I ever used was a 2430A. New in Dec '89. It had the Tekmate 2402 add-on PC module for I/O. I used this a lot working on my BSEE thesis in '91. I much preferred the way the cursors moved with the knob adjustments over a later TDS420 and many later an current scopes I have had to use in the past 30yrs.


Joerg
 

So I had some time to familiarize myself with my new toy. Going through the Operators Manual, I verified vertical and horizontal gains are all spot on. Also got a P6133 probe, albeit without the original BNC with readout pin - anyone with a spare?

Next I checked probe calibration. Up to 500kHz all is perfect
https://groups.io/g/TekScopes/photo/263696/3222975?p=Created,,,20,2,0,0

but at 5MHz, things go off the rails
https://groups.io/g/TekScopes/photo/263696/3222975?p=Created,,,20,2,0,0

Is this expected or something I should fix? Frequency is stable to within 1%. Also at 500kHz, duty cycle is only 46%. I currently don't have another function generator for further tests.

Cheers
Joerg


 

Considering the range indicated for the calibration/compensation signal tops out at 5 MHz I think that this is what should be expected. I have seen similar rounding off of the compensation square wave near the top of the range with other scopes of similar vintage. The main use for the calibration/compensation signal is to compensate the probes, and that can be done perfectly well at much lower frequencies.

Also, the calibration/compensation signal is essentially separate from the rest of the scope, so even if it were not working correctly that would not necessarily indicate problems with the rest of the scope (CAVEAT: I have a 7000-series scope that I am trying to repair where one of the symptoms of its malfunction was a wonky calibration signal. Of course the other symptom was that the CRT displayed something more like a Jackson Pollack painting than a proper oscilloscope trace, so YMMV. The bad calibration signal may have been the result of power supply issues, but I won't be able to verify that till I've completed repairs).

Older scopes will have a section in the service manual that takes you through a full validation of the scope's function. Newer scopes usually have some kind of self-test feature. I'm guessing that yours has self tests that can be run manually somehow. If you run those they should tell you if there's anything obviously wrong with your scope. Scopes with such self tests usually run them when you start the instrument, so if you are not seeing error messages when you power the unit up then I expect it is working within specs.

-- Jeff Dutky


Joerg
 

Hi Jeff,

thanks for your input. I have run all the self tests and the extended tests and they all pass, i.e. everything that I can test from outside the scope appears to be just fine. I guess In have to get my other scope up and running so I can make some independent tests - and finally get a function generator ;-)

Good luck with exorcising that action painting poltergeist from your unit!

Cheers
Joerg


Szabolcs Szigeti
 

Hi,

That is completely normal. The calibrator's waveform is expected to be
"bad" in the high range.
It is basically there just to give a quick check that you see a signal. The
calibrator changes its frequency with the sweep, so that you can always see
a couple of periods on the screen.
It is not specified to be anything exact shape in the high sweep ranges. It
works the same on all 24xx DSOs, so there is nothing wrong with your unit.
Probe calibration is to be done on lower sweep ranges anyway.

Szabolcs

Joerg <joerg.reichardt@gmail.com> ezt írta (időpont: 2021. máj. 8., Szo
0:47):

So I had some time to familiarize myself with my new toy. Going through
the Operators Manual, I verified vertical and horizontal gains are all spot
on. Also got a P6133 probe, albeit without the original BNC with readout
pin - anyone with a spare?

Next I checked probe calibration. Up to 500kHz all is perfect
https://groups.io/g/TekScopes/photo/263696/3222975?p=Created,,,20,2,0,0

but at 5MHz, things go off the rails
https://groups.io/g/TekScopes/photo/263696/3222975?p=Created,,,20,2,0,0

Is this expected or something I should fix? Frequency is stable to within
1%. Also at 500kHz, duty cycle is only 46%. I currently don't have another
function generator for further tests.

Cheers
Joerg






Joerg
 

Thanks Szabolcs, that's reassuring.
Cheers
Joerg


Joerg
 

So I finally got my old Hameg repaired - another capacitor short, this time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all spot on with about 5mV p-p ripple. The only one that that is not within a view mV of specs is the 8V which measures as 7.85V, that that is still just 2% shy. So I'm very pleased. I also measured the 10MHz on the top board and that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had laying around was the bandgap in an LT1365 which is 200mV. On both channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms / div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133). That is pretty spectacular I thought, but it also worries me a bit, because my Fluke 8840A tells me its somewhere near 202 mV although that meter has not seen a calibration in a long, long time I think 1% of accuracy should always be there (my Fluke also checks out against my other multimeter ...). I measured on two specimen of the chip, same result. The initial accuracy of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What further makes me skeptical that the readings change with Volts/div in the single percent range (I can kinda see that, you're getting toward the low / high end of the range) and time / div (I can also see that - on shorter time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter measuring DC voltages?


-
 

In my experience, a scope isn't a good instrument to use for measuring
voltages with a high degree of accuarcy. it's too easy to have parallax
errors on a scope and the lines themselves are too large for high
resolution readings. Scopes, IMO, are more for looking at wave FORMS
instead of voltages.

YMMV.

On Tue, May 11, 2021 at 5:41 PM Joerg <joerg.reichardt@gmail.com> wrote:

So I finally got my old Hameg repaired - another capacitor short, this
time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all
spot on with about 5mV p-p ripple. The only one that that is not within a
view mV of specs is the 8V which measures as 7.85V, that that is still just
2% shy. So I'm very pleased. I also measured the 10MHz on the top board and
that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had
laying around was the bandgap in an LT1365 which is 200mV. On both
channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms
/ div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133).
That is pretty spectacular I thought, but it also worries me a bit, because
my Fluke 8840A tells me its somewhere near 202 mV although that meter has
not seen a calibration in a long, long time I think 1% of accuracy should
always be there (my Fluke also checks out against my other multimeter ...).
I measured on two specimen of the chip, same result. The initial accuracy
of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What
further makes me skeptical that the readings change with Volts/div in the
single percent range (I can kinda see that, you're getting toward the low /
high end of the range) and time / div (I can also see that - on shorter
time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter
measuring DC voltages?






Szabolcs Szigeti
 

Hi Jorg,

Just look at the specifications of most of the scopes. They are usually not
specified for anything better than a couple of percent and that may even
change with the input level or the amplitude of the signal. Also, there can
be much linearity error allowed. So in summary, I don't use any scope for
accurate voltage measurement. I just use it to get a general idea of what
is where or do comparison measurements with a known accurate value.
But, you can do tricks, like triggering your 8840A at the moment when you
want to measure and use the scope to time the trigger signal, etc. So in
combination with other instruments there is a place for the scope in
accurate voltage (or basically anything) measurement.

Szabolcs



Joerg <joerg.reichardt@gmail.com> ezt írta (időpont: 2021. máj. 11., K,
23:41):

So I finally got my old Hameg repaired - another capacitor short, this
time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all
spot on with about 5mV p-p ripple. The only one that that is not within a
view mV of specs is the 8V which measures as 7.85V, that that is still just
2% shy. So I'm very pleased. I also measured the 10MHz on the top board and
that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had
laying around was the bandgap in an LT1365 which is 200mV. On both
channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms
/ div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133).
That is pretty spectacular I thought, but it also worries me a bit, because
my Fluke 8840A tells me its somewhere near 202 mV although that meter has
not seen a calibration in a long, long time I think 1% of accuracy should
always be there (my Fluke also checks out against my other multimeter ...).
I measured on two specimen of the chip, same result. The initial accuracy
of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What
further makes me skeptical that the readings change with Volts/div in the
single percent range (I can kinda see that, you're getting toward the low /
high end of the range) and time / div (I can also see that - on shorter
time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter
measuring DC voltages?