Author Topic: Restoration : Fluke 720A KVD/Ratio standard  (Read 17212 times)

0 Members and 1 Guest are viewing this topic.

Online Vgkid

  • Super Contributor
  • ***
  • Posts: 2414
  • Country: us
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #75 on: September 11, 2017, 06:45:15 am »
I have unit with same symptoms. But I was unable to find the spare part switch. Is this switch still available on market?
Switch info here:
http://www.eevblog.com/forum/metrology/4-wire-switch-selectable-resistance-standard/msg1193999/#msg1193999
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline Echo88

  • Frequent Contributor
  • **
  • Posts: 457
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #76 on: September 11, 2017, 06:55:39 am »
Thanks for the info. I will try to repair the switch next week with epoxy and hoping for the best, while searching on ebay for a similar one.

Also: Got the KVD running again after carefully rotating the shaft with the brushes in the S8-function switch to the OPR-function with long nose pliers and soldering it back in for a sanity check. It performs beautifully, apart from the 7. decade which seems to be partly corroded on the switch and therefore gives false readings in some positions.
 

Offline Echo88

  • Frequent Contributor
  • **
  • Posts: 457
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #77 on: October 01, 2017, 08:10:28 pm »
I could successfully repair the S8-switch by cleaning and then glueing (epoxy, "Uhu Endfest 300") the metal-thread-shaft from the switch-front to the remains of the plastic-shaft, which rotate the bushings. The switch now performs really nice and hopefully lasts as long as i use the KVD (fingers crossed).

Since the plastic shaft was badly damaged and very short, i didnt see any possibilty to repair the switch by means of a shaft coupler, therefore i used the glue as a last resort. If the switch breaks again at some point, it might be not repairable anymore since one cant open it due to the glueing (if it doesnt break at the glued shaft-transition).

 

Offline TiN

  • Super Contributor
  • ***
  • Posts: 3667
  • Country: tw
  • xDevs.com
    • xDevs.com
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #78 on: July 06, 2018, 10:25:43 pm »
Time to come back to this poor abandoned project.

What is better than fixing Fluke 720A??  :popcorn:



Fixing two of them! Second one got delivered today.

Somebody vandalized poor KVD, and gutted kelvin-varley potentiometer for bridge balance (lucky for me, I have one spare!) and Fluke factory trim low ohm (4-6 ohm) wirewounds for decade A calibration.  :wtf:



Perhaps after some time, previous owner got hit by regrets and remorse, so they included a bag with removed wirewounds in the package. All but missing one  :popcorn:



Lucky for me again, i have 10+pcs of these too.

I guess idea is to play some tetris to find the proper ones to go proper spots...  :-/O



TBD...
xDevs.com YouTube | Have test gear documentation to share? Upload here! No size limits, firmware dumps and teardown photos welcome.
 

Offline Echo88

  • Frequent Contributor
  • **
  • Posts: 457
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #79 on: July 06, 2018, 11:37:05 pm »
And after that you can use both KVDs to rebuild the setup from the Jim Williams AN86 with 3x 3458A and "spend
many delightful hours “surfing the Kelvin”".  :)
 

Offline TiN

  • Super Contributor
  • ***
  • Posts: 3667
  • Country: tw
  • xDevs.com
    • xDevs.com
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #80 on: July 06, 2018, 11:41:57 pm »
I'm missing 3rd 3458....  :palm:
xDevs.com YouTube | Have test gear documentation to share? Upload here! No size limits, firmware dumps and teardown photos welcome.
 

Offline ManateeMafia

  • Frequent Contributor
  • **
  • Posts: 712
  • Country: us
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #81 on: July 07, 2018, 12:16:15 am »
Put a 2002 in 3458A emulation mode. No one will ever know.
 

Offline e61_phil

  • Frequent Contributor
  • **
  • Posts: 666
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #82 on: July 07, 2018, 03:27:21 am »
Put a 2002 in 3458A emulation mode. No one will ever know.

I doubt that ;)
The 2002 isn't nearly as linear as the 3458A. It is more in the league of a 34401A (talking about linearity only)
 

Offline TiN

  • Super Contributor
  • ***
  • Posts: 3667
  • Country: tw
  • xDevs.com
    • xDevs.com
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #83 on: July 18, 2018, 08:03:40 pm »
The 2002 isn't nearly as linear as the 3458A. It is more in the league of a 34401A (talking about linearity only)

Maybe 2002 isn't as linear as HP, but saying K2002 is in league of 34401a is understatement at least :)
Here's what I got from today's test on one of the meters.



If we stay over 15% of the FS, then total system (MFC+DMM) linearity is <0.2ppm.
xDevs.com YouTube | Have test gear documentation to share? Upload here! No size limits, firmware dumps and teardown photos welcome.
 
The following users thanked this post: e61_phil, Le_Bassiste

Offline e61_phil

  • Frequent Contributor
  • **
  • Posts: 666
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #84 on: July 18, 2018, 09:53:33 pm »
Hi Tin,

to what value are your ppm's referenced to? 20V?

I attached the meaurement of my HP 34401A after ADC adjustment. Deviation is referenced to 10V. The measurement attached is measured against my Fluke 5440B. A measurement against a 3458A looks quite similar.

This kind of linearity is what I measured over and over again on many 34401A's. Dr. Frank showed similar results here in the forum.
It seems to me that the Multislope III is much better in linearity than the (faster) Multislope IV (beginning with 34410A to the actual units).


Edit: Here I measured the Keithley 2002 against two 3458As. For me it looks like the K2002 is in the league of a 34401A (we are talking about linearity only!)
http://www.eevblog.com/forum/metrology/dmm-linearity-comparison/msg1354870/#msg1354870
« Last Edit: July 18, 2018, 10:04:44 pm by e61_phil »
 
The following users thanked this post: TiN

Offline TiN

  • Super Contributor
  • ***
  • Posts: 3667
  • Country: tw
  • xDevs.com
    • xDevs.com
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #85 on: July 18, 2018, 10:29:52 pm »
Reference is to calibrator output value, not range. I can try your script once I have meters free (this test was part of my calibration check report procedure, its not targeted to pure INL tests anyway).
« Last Edit: July 18, 2018, 10:31:38 pm by TiN »
xDevs.com YouTube | Have test gear documentation to share? Upload here! No size limits, firmware dumps and teardown photos welcome.
 

Offline meandeev

  • Contributor
  • Posts: 24
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #86 on: October 08, 2018, 05:57:58 am »
I bought a 720a from a legacy in unknown condition and the shafts are broken, too. Also ALL plastic standoffs are broken, as lowimpedance wrote.

...
One interesting mechanical failure which I suspect most of these oldies suffer from is the acrylic standoffs craze then crack and fall apart. see pic.
...


What material are these plastic standoffs? Can I use PMMA/Acryl tubes for this?

@TiN:
Which material and technology did you use for the black shaft? (It seems not the "normal" FDM-3D printing. It looks like ABS with injection molding technique...)
I can see, that your standoffs of the faulty wired switch are also made of a different white material. Do you know, what it is?


Taking of shafts.

I'm replacing acrylic bad ones with plastic from my 720A parts box. Took few quick measurements to make 3D CAD in case some poor voltnut want to 3D-print some, as I don't have access to this advanced technology.

....


 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1159
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #87 on: October 08, 2018, 06:08:37 am »
Looks like some thermoset material. FDM printed thermoplastic material would probably be to soft and could break pretty easy. Maybe you can use extruded PMMA, if you plan to machine them. If you plan to print them, you can use SLS parts that have been infiltrated  or use DLP printed resin parts.

-branadic-
Prema 5000 | 2x Prema 5017 SC | GenRad 1434-G | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline TiN

  • Super Contributor
  • ***
  • Posts: 3667
  • Country: tw
  • xDevs.com
    • xDevs.com
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #88 on: October 08, 2018, 07:44:09 am »
Replacement black shaft is not 3D printed , it is spare part from other 720A.
xDevs.com YouTube | Have test gear documentation to share? Upload here! No size limits, firmware dumps and teardown photos welcome.
 

Offline meandeev

  • Contributor
  • Posts: 24
  • Country: de
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #89 on: October 12, 2018, 07:46:51 am »
Now I used 4/10mm PMMA (acrylic plasic) tube for the standoffs (see the picture). The original screw sockets fit very well  :-+
For the broken shafts: a few drops of dichlormethane make them strong again (so it seems it´s really PMMA!)

But then I measured the input resistance: 80k-ohm. I´m afraid of a broken decade A switch  :palm:

to be continued...

 

Offline LKM

  • Contributor
  • Posts: 5
  • Country: us
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #90 on: October 18, 2018, 06:12:19 am »
Hello all - I've been watching this thread with interest as I have a sick 720A here with a broken shaft coupler. I bought some replacement couplers from Fluke recently - I will post a picture and P/N in a follow-up later.

I was wondering - can anyone recommend a procedure for removing/replacing the couplers for example in decade B or C? Is everyone taking the dials off? I'd like to minimize how far I have to disassemble the unit.
 

Offline LKM

  • Contributor
  • Posts: 5
  • Country: us
Re: Restoration : Fluke 720A KVD/Ratio standard
« Reply #91 on: November 27, 2018, 04:57:36 pm »
OK, much delayed but as promised current Fluke P/N for these shafts is 701979. I've attached a photo of the order envelope.

Also attached is a photo showing the 720A mid-replacement on one of the decade switches. I marked the dial position with some nail polish but a sharpie would work as well. I then loosened the two dial set-screws and unscrewed the metal coupler thing mounted to the bulkhead. This let me slide the metal shaft out the front just enough to play Operation and get the old broken acrylic shaft out and get the new black plastic (Nylon?!) one in. Buttoned it all up and the switch works great.

One caution is that some of the new black shafts have molding artifacts and may not slide freely into the multideck switches. I'll probably have to trim the worst ones before installation.

Hope it helps someone. 
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf