Datron 1071 repair

[feedback.loop]

A vintage metrology grade meter was repaired, calibrated and tested for stability. Not much was wrong with it: a couple of faulty caps, a stuck switch, and corrupt calibration data. The display is bad as well, but usable, so it can be tolerated for now. The loss of calibration is, of course, a big deal since I don't have appropriate equipment to calibrate a 7.5-digit meter, but I have done what I could given the circumstances. Then I run the meter together with HP 34401A for about 28 hours taking measurements of 10V from Fluke 341A calibrator over GPIB and plotting the data using Octave 4 with instrument-control package. The results look good: just a few ppm of drift over a wide temperature range, and the meters stayed within about 2.5 ppm from each other.

Datron 1071 Service Manual: http://www.ko4bb.com/manuals/66.228.162.56/Datron_1071_Multimeter_Cal_and_Service_Handbook.pdf

https://youtu.be/jcCC867gKXE

[bitseeker]

Thanks for making another repair vid. I look forward to watching this tonight.

[The Soulman]

  Thanks for sharing!

Are you sure the display itself is broken and not some of the driving circuitry?
There is to much of a pattern for my taste, I don't know, just a guess..

[Vgkid]

Thanks, will watch tonight.

[feedback.loop]

Thanks for sharing!

Are you sure the display itself is broken and not some of the driving circuitry?
There is to much of a pattern for my taste, I don't know, just a guess..

I am not entirely sure, but I couldn't find anything wrong with driving circuitry. And I vaguely remember seeing some posts about replacing such displays with ones from broken donor units.

[Dr. Frank]

Nice story telling. Good pace.

I also would think, that there are some bad solder junctions, or so, as the display shows too many correlated faulty segments.
Good luck for the repair.

You sound similar to TiN (which both is quite pleasant),
Do you also have an origin from Russia, or from neighboring states? (no degradation intended!)

Frank

[feedback.loop]

Nice story telling. Good pace.

I also would think, that there are some bad solder junctions, or so, as the display shows too many correlated faulty segments.
Good luck for the repair.

You sound similar to TiN (which both is quite pleasant),
Do you also have an origin from Russia, or from neighboring states? (no degradation intended!)

Frank

Well, I will try to look again into the display circuitry, but it looked fine on the first glance.

Yes, I am from Russia originally. Same accent. It is hard to get rid of the accent if one learns a second language as adult. And I am sure I make mistakes from time to time with grammar and pronunciation.

[bitseeker]

Some accents are very heavy. I find yours easy to understand. Keep up the good work!

[lowimpedance]

I thought the voice sounded familiar ! , I had seen your fluke repair on youtube before  .
As for the display I thought I had seen another couple of threads relating to cathode poisoning on these panaplex/nixie displays in the past, so see here:
https://www.eevblog.com/forum/beginners/gas-discharge-display-of-datron-4000-problems/?nowap
Note Gilbenl s reply with some links that may be useful.
And given you have replaced the HV cap I suspect it is indeed a worn out display  .

[Vgkid]

Nice job on the repair so far. I think I have heard of someone replacing the panaplex display with a LCD display, though that might be for arcade purposes.

[macfly]

> It is hard to get rid of the accent if one learns a second language as adult. And I am sure I make mistakes from time to time with grammar ...

Thank you very much for this report - and don't worry about your accent. Your English is very good understandable.
Some of the native-english speaking fellows talk so fast and with dialect, which is sometimes absolut incomprehensibil for those, who learned
only Oxford English at school (sorry fellows  ).

Regards,

macfly
 

[guenthert]

Thanks for sharing and sorry for not being able to help with the repair of the display.  I was wondering instead about those diodes you identified as voltage reference in the DMM.  Is this the Williams' 'ring of two' configuration (there should be a NPN/PNP transistor pair nearby)?  I got away with the impressions that surface Zener diodes generally are noisy and age poorly, so I'm surprised to see them used as reference in a long-scale DMM.  Do subsurface, discrete Zener diodes exist (in a two-terminal package)?

[TiN]

Nice work, hope to see more on this box in future. Overall concept of design seem to be very similar to higher end 1271/1281.

[dacman]

I believe that those orange plasma displays have a voltage rating of 220 V peak max.

[Johnny10]

Thanks for another interesting video.
I believe I have watched all of them!

It would seem you are collecting a good assortment for your lab.
Would be great to see your whole setup.

[zlymex]

I once own a Datron 1071 and the reference is dual zener based(D59, D60). They didn't say anything about the maker and type, but I can see from the teardown photo that they were 1N829A.

My questions are:
Is 1N829A a subsurface Zener by any chance?
Do subsurface, discrete Zener diodes  in a two-terminal package exist? (repeat)

I don't have any 1N829 for test, but one of my friends has tested a 1N829 by his 3458A when power up. I don't recall any parameters(such as the current, NPLCs for 3458A) but here is the chart

I calculated the stdev in excel for 100 consecutive data to be 0.038ppm, which is good.

[Andreas]

Hello Lymex,

the 1N82x series is a temperature compensated zener
(standard surface zener combined with a normal diode to compensate for T.C.)

There is a "zero TC" current (between 4 and 11 mA) where the T.C. is nearly zero over a 10 deg C temperature span.
So you will have to adjust the current individually after having sorted out the unstable zeners.

At least I dont know any discrete subsurface zeners.
I know them only as part of a integrated cirquit (LM329, LM399, LTZ1000, AD586, LT1021 ...)

With best regards

Andreas

[zlymex]

I had several batches of 2DW23x that are also temperature compensated Zeners. The datasheet doesn't tell anything about the type neither, but the LF noise is much smaller than the best commercial Zeners (such as LTZ1000). That's why I suspect that there is any relationship between Zener type(such as whether buried or not) and the noise.

[feedback.loop]

Thanks for sharing and sorry for not being able to help with the repair of the display.  I was wondering instead about those diodes you identified as voltage reference in the DMM.  Is this the Williams' 'ring of two' configuration (there should be a NPN/PNP transistor pair nearby)?  I got away with the impressions that surface Zener diodes generally are noisy and age poorly, so I'm surprised to see them used as reference in a long-scale DMM.  Do subsurface, discrete Zener diodes exist (in a two-terminal package)?

Regarding the configuration: there is a dual reference supply +-6.37 V. See the attached schemaitc

[feedback.loop]

I believe that those orange plasma displays have a voltage rating of 220 V peak max.

You probably mean to say why the capacitor was rated for 450V. I later found in the service manual that it must be 350V. Someone replaced it with 450V one.
The display segments are driven from +5V to -175V.

[Gyro]

Replacement selected 1N82x reference diodes from Datron were supplied as a matched zener and resistor pair. I don't know if the resistor was simply selected to set to optimum zero TC zener current, or whether there was any resistor TC matching involved too.

[dacman]

I believe that those orange plasma displays have a voltage rating of 220 V peak max.

You probably mean to say why the capacitor was rated for 450V. I later found in the service manual that it must be 350V. Someone replaced it with 450V one.
The display segments are driven from +5V to -175V.

I happen to know that there is (usually) about 280 Vdc across that capacitor.  The voltage gets dropped down to -175 Vdc with a series transistor regulator.  It's referenced to the +5 Vdc digital power supply.

What I was getting at, is if the display is suffering from cathode poisoning and it was desired to fix it by using double current or more for a time, then it seems to me that this would need to be accomplished by doubling the voltage, which I would not want to do with the display in the unit.  I'd also want to monitor the current draw in case the current increase was not linear.

[gilbenl]

Haven't had a moment to watch the video, but the 1071 is a great meter. Mine lacks the GPIB interface, which I plan to add at some point. A ROM dump from the GPIB board would be appreciated!

Regarding the display--I have a 1062 with the same fault. Unfortunately, I could never undo the cathode poisoning. There's very good info in the service manual regarding the display workings and a retrofit with a modern alternative should be doable, however, I haven't attempted. Alternatively, there are NOS and salvage Panaplex displays on ebay. They're not the purpose made datron units, but should be a serviceable replacement.

Theres a very slight chance that the issue is not with the display itself, but with the PS or driver board. Check the caps if you haven't.

[feedback.loop]

Teaser 

[ManateeMafia]

Looking forward to it.

I have some Datron gear with broken displays but I have no time to fix them.