Author Topic: Repairing a 5440B/AF DC Calibrator  (Read 9108 times)

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Offline singapol

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #25 on: July 16, 2016, 01:51:58 pm »
Take note if you have replaced Q1-4 with 2n3904/2n3905 it will fail soon as the max. continuous collector current is only 200mA vs 600mA of 2n4401/2n4403.  :o 6 SN75518 driving VFD is no joke.
« Last Edit: July 16, 2016, 01:53:38 pm by singapol »
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #26 on: July 16, 2016, 03:24:56 pm »
Thanks Singapol - I was looking to use those jelly bean 390x's in case the transistors in the unit had failed. When I took them out and tested them they were fine.

I reinstalled all the components and put a 10uF electrolytic in place of the 6.8uF tantalum (will need to get a proper replacement) for testing and...drum roll...

IT LIVES!



Came up with no errors I think - some characters on the right display were it now says 'voltage mode' but then straight to this display.

They look nice and bright so I'm going to see if I can find a replacement tantalum locally and make that swap otherwise I'll order one and then reassemble the front to see if it really lives or if it's just mostly alive.

Thanks everyone for the help so far.

TonyG
 
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Offline Kleinstein

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #27 on: July 16, 2016, 03:31:30 pm »
Those drop like yellow tantalum caps are known to fail quite often. So even if a few of them are still Ok, it might be a good idea to replace them - they sometimes do fireworks, not just a short.

For the filtering cap C1 and in many other positions low ESR electrolytic should be Ok too, unless you want to use the instrument at freezing temperatures.
 

Offline ManateeMafia

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #28 on: July 16, 2016, 03:35:12 pm »
Congratulations  :-+

I hope all goes well once you get it back together. Do you have the gear to calibrate it or do you plan to send it out?
 

Offline SeanB

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #29 on: July 16, 2016, 03:41:29 pm »
Looking at the ceramic that came out it looks a lot like drywall gypsum crumbs, and as well the inlet by the fan shows dust, which might be that it was in an area where a remodel occurred and the dust got inside, along with a few larger clumps of drywall interior. Then it was packed with this still inside.

Leave the electrolytics you put in as C3,4 and up the voltage to 63V, they are being used as DC isolation to prevent the core saturating as duty cycle changes, and this is a very bad place to use a tantalum, so an electrolytic capacitor ( or even better a ceramic capacitor, though there the voltage drop of capacitance might need 200uF of capacitance to get an effective 10uF capacitor at 30VAC) is a lot better, and a higher voltage as well as the cathode foils are formed to a higher voltage so will last longer. slightly bigger, but there is plaent of room to lay them down sideways and stake to the board with a drop of superglue.
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #30 on: July 16, 2016, 04:13:39 pm »
Thanks everyone for the support and suggestions - Appreciate it - I checked my local store's web page and they don't have the same spec tantalums (or electrolytic) so I put the unit back together to give it a try out.

Kleinstein - Thanks for the comments - There are only a few caps on the board so I'll follow your suggestion and replace them all - I assume that Fluke went with the tantalum cap for the filter because of the low ESR and the temperature stability - Maybe they just had a bunch of them already.

ManateeMafia - This, along with a 5200A are my first forays into owning an actual calibrator. I got this 5440 for $210 or so from a DoD auction (cost me $263 to ship it too me) and bought the 5200A based on what I've read here on the board and some hints/guidance from Dr. Frank. I live just down the road from the Fluke Cal home base so I was going to get them up and running to the point of my gear here and then drop them off for an official Fluke cal - As I can drop off and pick up, I can save a lot in shipping these monsters around.

SeanB - I never did find where that stuff came from - It really reminded of the ceramic core of an old wire wound resistor or an old ceramic isolator but I can't find anything like that anywhere in the system so your theory is better than anything I had. I'll up the voltage on C3 & C4 when I order the tantalums from DigiKey and replace them on the board.

So far I have the unit warming up - The Service manual says that it needs an hour to do the analog self test so that the ovens are warm - Will check back in with the results when that is done.

I did plug it into my DMM to see if it generated output and it does - No faults so far - Here is a photo of the front panel:



The VFD is OK - The right one seems flawless, the left one doesn't have that gap as the photo shows (shutter speed etc) but it is a little dimmer than the right - The 3rd last 0 is actually quite bright - It's more than good enough to work with though.

TonyG

Online Dr. Frank

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #31 on: July 16, 2016, 05:00:50 pm »
Great. You got one of the best DC calibrators for a real bargain.

Use the left/right arrow to move the selected digit.. i.e. the highlighted one.
That's no fault, either. Use up/down to change value.

Unit needs 4h to fully stabilize. Then do an internal cal... autocal.. and check 11, 22, 250 and 1000V range with DMM.

In fact, you will instead check the range calibration of your DMM.

Frank
« Last Edit: July 16, 2016, 05:28:53 pm by Dr. Frank »
 

Offline RobK_NL

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #32 on: July 16, 2016, 05:32:49 pm »
In fact, you will instead check the range calibration of your DMM.
Unless that DMM is a freshly calibrated 3458, of course  :)

There's two 5440B's coming up for sale in the very near future ...
Tell us what problem you want to solve, not what solution you're having problems with
 
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Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #33 on: July 16, 2016, 05:42:03 pm »
Thanks Dr. Frank - Just tried using the arrows and it's exactly as you say.

The service manual said give it two hours warm up so it was in the middle of the internal cal when I saw your post - I'm going to put the covers back on and then let it warm up for 4 hours and redo the internal cal.

Where it sits right now, with my Keithley 2015 - 6 1/2 digits but no idea on complete accuracy yet:

Set          DMM
0V           -000.0009mV
11V         11.00037V
22V         21.9998V
250V       249.993V
1000V     999.962V

Seems reasonable to me - Will have to see what it shows when everything has warmed up.

A problem did leap up, the 2 button just fell off:



If you look closely you can see some epoxy on the connector so it has broken some time in the past and was glued on - I'll have to redo that.

TonyG

Online Dr. Frank

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #34 on: July 16, 2016, 06:00:49 pm »
Well., your DMM is probably out of cal, as its ranges do not fit, and your DMM is of the 20..30 ppm class.
Use 1.9 V, 10V / 19V, 100V / 190V and 1000V as Cardinal Points, instead. 1000V needs 30sec settling time, at least.
Downranging from 1000V the same

Frank
« Last Edit: July 16, 2016, 06:55:11 pm by Dr. Frank »
 

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #35 on: July 17, 2016, 01:30:44 am »
So close but yet so far, while I was waiting for the 5440 to warm up for 4 hours the switch I had repaired has now become stuck down:



Even though I was very careful and only applied a small amount of glue, the only thing I can think of is that some of it still made it's way into the side of the switch.

According to the parts list the switch is:

    Switch, Pushbutton, SPST, Keyboard FLUKE STOCK NO 513473 MFRS SPLY CODE 89536 MANUFACTURERS PART NUMBER 513473

This is a Fluke part - Probably unobtanium - I tried spraying a bit of IPA into it to clean it out and I can move the switch but it just doesn't spring back when pressed in.


Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #36 on: July 17, 2016, 01:58:41 am »
The switch is heat staked together at the corners - Using an exacto knife I cut through the heat stake and here is what is inside:



You can see the cruft on the left side of the upper switch casing - I'm going to see if I can clean that out and then super glue the assembly back together.

That said, if anyone has any of these they'd be willing to part with please let me know.

TonyG

Offline Vgkid

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #37 on: July 17, 2016, 02:01:22 am »
Nice job so far. Good luck fixing the switch.
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Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #38 on: July 17, 2016, 03:19:16 am »
Thanks - I have the switch fitted back together for testing:



It works like the others do - Not quite a smooth but almost. Took a nail file, Exacto knife and small screwdriver to it and cleaned it out I think.

Plan to take a little relax before gluing it back together as this has been somewhat stressful (my own fault but still stressful).

TonyG

Offline nidlaX

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #39 on: July 17, 2016, 04:16:05 am »
So close but yet so far, while I was waiting for the 5440 to warm up for 4 hours the switch I had repaired has now become stuck down:



Even though I was very careful and only applied a small amount of glue, the only thing I can think of is that some of it still made it's way into the side of the switch.

According to the parts list the switch is:

    Switch, Pushbutton, SPST, Keyboard FLUKE STOCK NO 513473 MFRS SPLY CODE 89536 MANUFACTURERS PART NUMBER 513473

This is a Fluke part - Probably unobtanium - I tried spraying a bit of IPA into it to clean it out and I can move the switch but it just doesn't spring back when pressed in.
Here's your keyswitch: https://deskthority.net/wiki/Datanetics_DC-60_series. If you are in need of replacements, you might go hunting for some Fluke Y1700 keyboards: http://sandy55.fc2web.com/keyboard/y1700.html. I see that they've been sold for cheap on eBay recently. On the Deskthority wiki page, there's a link to an AliExpress auction for some switches standalone, so those may pop up every once in a while.

Sadly, keyboard / keyswitch knowledge is about all I can contribute to this thread. :-//
 
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Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #40 on: July 17, 2016, 04:52:39 am »
That is awesome - thanks nidlaX - I'll put a search into eBay to get some "backups".

TonyG

Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #41 on: July 17, 2016, 07:17:52 am »
And finally back to where I started this morning at:



Goals for tomorrow:

1. Warm up 5440 for 4 hours
2. Don't screw it up
3. Run Internal Cals

Thanks everyone for the support and information.

TonyG

Offline Kleinstein

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #42 on: July 17, 2016, 08:48:32 am »
If I see it right from the plan C3 and C4 are used back to back for DC isolation of the transformer. Not a really good solution to use tantalum caps here. The way better solution would be a single non-polarized cap, like those used for audio. Two 15 µF in series is only 7,5 µF - this is still possible with film caps (though larger size) and modern MLCC ceramics (e.g. 2 times 4.7 µF in parallel), as the voltage should not be that high and the size of the caps is not critical.

As the current is limited fireworks are not that likely. The one failure was a non smoker so far.
 

Online TiN

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #43 on: July 17, 2016, 12:37:16 pm »
Those key caps and binding posts just beg for some hydrogen peroxide action ;)

Nice work, now you only have 3458A missing... Oh, I said only? What a mistake..
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Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #44 on: July 17, 2016, 03:43:45 pm »
I turned the machine on 3 hours ago so I have another hour to wait till I'll run the internal cal routine again but I thought I'd try out the Error Display with my Keithley 2015:



Working out the values for error mode from the 1 year specs for the 2015THD:

Range (V)Input (ppm)Range (ppm)Input (%)Floor (uV)
0.150350.005350
13070.003700
103050.0035000
1004560.004560000
10004560.0045600000

The actual results I get are:

Range (V)ERR (ppm)Pass/Fail
0.1-37Pass
1-33Pass
1034Pass
100-6Pass
1000-34Pass

Looks like things are working and will only get better with the cals.

TonyG
 
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Offline Tony_G

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #45 on: July 17, 2016, 05:06:49 pm »
Just finished all the internal self tests (digital, analog & high voltage) and the ran the internal calibration.

It seemed to make a big difference w.r.t the divider (I turned it on in the previous measurement to get more resolution in 100mV & 1V range). As this applies only to those ranges here is the change:

Range (V)ERR (ppm)Pass/FailPrevious ERR (ppm)
0.1-62Pass-37
1-35Pass-33

so it seemed to make a big difference to the 100mV range.

Without using the divider I see this:

Range (V)ERR (ppm)Pass/FailPrevious ERR (ppm)
0.140Pass-37 (divider)
134Pass-33 (divider)
1034Pass34
100-69Pass-6
1000-21.7Pass-34

I'll need to go away and read the theory of operation in more detail to see what it says about the divider (you can't use the external sense with it. Also the 2015THD inputs in 100mV and 1V ranges are rated at >10Gohms) to understand why the difference but as you can see it passed my Keithley in either case - Now is the Keithley anywhere near spec? I don't know but once I have Fluke run the 5440 through an external cal I should be able to tell for DC at least.

Thanks everyone for the comments, suggestions and guidance (especially the guidance).

I'll be swapping the 5440B/AF from the workbench and moving onto the next item:



TonyG

« Last Edit: July 17, 2016, 05:23:48 pm by Tony_G »
 
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Online Dr. Frank

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Re: Repairing a 5440B/AF DC Calibrator
« Reply #46 on: July 17, 2016, 05:32:22 pm »
The divider is quite unstable, and needs to be calibrated externally, quite often.

If you generate 0.1 and 1V on the 11V, you will have the non-linearity problem. The DAC is linear to 0.2 (measured) .. 0.5 (spec.) ppm, so 1V may be precise to about 2..5ppm, 0.1 V to about 20..50ppm..
Make sure to do a good zero on the Keithley (i.e. output 0V from the 5440A, and zero the 2015, then output 0.1 and 1V).

I thought, the 2015 would have 1.9x "overrange", for each range.. compared to 1.2x of HP DMMs.

Then you could test with 1.9V for the 1V range, 10V for the 10V range, both are same range on the 5440A, so only the linearity uncertainty applies.


Anyhow, the Keithley may be inside its 1yr. specification, but the 5440A reveals, that it has been drifting a lot since the last calibration.

A sign of that is that the 10V range drifted + 34ppm, compared to the others, which drifted in the negative direction.. Even if the 5440 would be outside its spec (maybe a few ppm), then all of these 10:1 ratios of the 2015 can be checked precisely.
The 5440 makes very accurate 10:1 ratio calibrations for those 4 ranges, I assume, even better than the 57x0As.

Frank
 
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