Author Topic: Restoration glory of Keithley 2001 DMM  (Read 203486 times)

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Online TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #625 on: October 15, 2016, 01:10:21 am »
Good point from Le_Bassiste! Could be very possible, as that cable is the only interface between digital brains and analog world. Optocouplers near cable are another component worth checking.
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Offline lukier

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Re: Restoration glory of Keithley 2001 DMM
« Reply #626 on: October 22, 2016, 05:22:12 pm »
Finally, I managed to repair my 2001, I think.

My meter had most of 200.x and 200.1 errors. Leaky old caps on the digital board (replaced) and somebody replaced the caps on the analog board around 2004-2007 (replaced those as well and the fan too). All the supplies seemed ok, but the errors were still there.

I found that resistors through which +-15V is supplied to the NE5534 on the ADC board are broken. One burned badly, leaving tar on the PCB, second one failed on high resistance/open. Replaced these resistors as well.

I've tried running comprehensive calibration, but it failed during open inputs step with error 354 = "200 mV offset out of spec". Then I've started chasing red herrings, replaced diodes in the power section, replaced the shift registers, some of the DG switches, NE5534 on the ADC board, desoldered the optoisolators and tested them on a protoboard - nothing helped. After all this messing around things got even worse and a dozens of new errors appeared.

But with TiNs help and some legal tender I got a new ADC board. With that I was able to run the calibration procedure with some poor artifacts (linear psu, 20k and 1M from a DIY decade). Things improved massively and I was only left with the errors that kada and SKE had: 200.1, 200.6, 200.7, 201.2 and turns out these can be fixed with upgrade to A08 (from A06). So once I got an UVC lamp (only had UVB) and a special PLCC44 adapter (the one I got with TL866 didn't work with 27C4096) I've upgraded the firmware and self tests passed.

I've started measuring some resistors that TiN kindly gave me, along with measurements from his 3458A, and I've noticed completely bonkers measurements on the megaohm ranges.

Now I wanted to improve things a bit, peroxide treatment (but the 25 year old paint on the display lens didn't survive kapton tape :/) worked nicely and while I was going to order DS1245 for MEM2 option I've ordered slightly better calibration artifacts, because I don't have anything top notch yet (multi-LM399 or LTZ1000) from Farnell: Y006220K0000T9L (20K 0.01 1 vishay-ppm/C), PTF651M0000BZEK (1M 5ppm/C), two ADR01BRZ to put in series and LT5400BCMS8E-8 9K/1K divider to divide ~20V to 2V.

And with these the calibration failed! Error 385, 20 MOhm 2W gain out of spec. High ohm resistors are a nuisance so I figured out that my soldering spree panic on the analog board left a mess affecting ohms current sources. After cleaning everything under a microscope, every guard trace, resistor cases, with dozens of cotton swabs and isopropanol the calibration worked!  :-+ I could even measure 1GOhm resistor.



Important lesson here is that self-test depends heavily on the calibration constants (which may be wrong or corrupted) and even these elaborate self-tests don't test everything that comprehensive calibration procedure tests. I still wonder what killed the resistors on the ADC board and worry that there might be something more wrong (a lot of the stuff is connected to +-15V rails).

I calibrated K2001 against my 3457A, as it seems most stable and extremely well aged (this one was closest to the resistance measurements done by TiN). Also, I really like this meter as it has most functions quickly available from the front panel, has offset compensation, 3 GOhm range, some autocalibration, no VFD but then I don't have to worry and it often runs 24/7 (also no fan) and does 7 digits in math mode - averaging. Unfortunately, it is not otherwise volt-nut friendly due to 3V front end arrangement. Transfer accuracy from a multimeter to a multimeter using some random voltage references wasn't that great, but none of my meters are calibrated anyway, it was more of a sanity check. Funny thing, when the GPIB cable is connected I get 104.1 error (GPIB handshake) but GPIB seems to work otherwise (well just *IDN? from ibtest, need to test more, luckily I have some NAT9914 chips at hand).

Now the meter occupied the last available space on my workbench and I want to build a more stable reference (multi-LM399 or maybe LTZ1000) and check how stable the meter is, drift, tempco maybe, etc. I also need to test some other functions (AC, current) more in depth to double check if there are no surprises that self-tests don't catch. Performance verification, even basic one, of such meter is definitely not an easy task.



Then if it turns out it is roughly OK I'll have to probably calibrate (low level calibration) this meter. I don't feel like spending more on the calibration than on the meter, also Tektronix has been annoying me for a long time, either once I wanted to buy 2000 benchkit parts and they gave me silly lead times, or other times I had to create an account there, as I was downloading TLA stuff or I wanted to download a datasheet for an SMD oscilloscope probe that I got off ebay. It was enough to trigger their marketing department and I started getting annoying phone calls. Now they stopped calling, but I still get emails telling me to buy TBS2000 or other crap - they seem really desperate. Anyway I couldn't even find UKAS Schedule of Accreditation for Tektronix (not that I need certificates, I was just curious on the DC 10V specs, Keysight UK has 0.8ppm). I'll ask RS Calibration for a quote. On their price list it says 62 GBP for a bench meter. They might not do 7.5 digit, but at least they could transfer whatever they have currently in their Fluke calibrator - better than nothing. I hope they have GPIB scripts for K2001.

Overall, I quite like this meter. Maybe not as much as 3457A, as I have to go through multiple menus and the average display from readings stored in a buffer are using engineering notation with only 4 digits after the decimal point, but on the positive side it has big VFD, sensible ranges with GOhm impedance up to 20V, thermocouples and similarly to 3457A offset compensation as well as scanner card option.

I would like to thank the forum members for helpful posts here and TiN in particular for providing me the ADC board, as well as putting a lot of effort on writing articles about his repair adventures - it probably takes as much time to write and take pictures as it takes to repair some things.
 
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Online TheSteve

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Re: Restoration glory of Keithley 2001 DMM
« Reply #627 on: November 03, 2016, 04:38:34 am »
How about credit where credit is due? I mentioned this technique in TiN's K2000 thread here. I came up with this crazy idea one day, decided to try it on a Keithley 199, and it worked like a charm. I am certain that I am not the first to do this but I hadn't heard of anyone doing it.

Received an Agilent device today with an extreme dent in the front face - very extreme! I've used heat before to form plastic and it has worked so/so. Thought I'd give it a go tonight when I remembered this thread.
I think it turned out very good. The heat was probably a little bit high from my heatgun but there was never a chance to make it look 100% original. The main goal was to get it back into shape so that when a rubber boot was put on it was completely hidden. With the original dent it was very obvious and looked terrible even with a rubber boot in place.
VE7FM
 
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Online zucca

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Re: Restoration glory of Keithley 2001 DMM
« Reply #628 on: November 03, 2016, 08:58:55 am »
Thanks lukier! Congrats!

One day I will write a post like you, my K2001 is still under my bench  |O .

A couple of little questions...

the one I got with TL866 didn't work with 27C4096

Why? Not fitting well... made in China crap?

but the 25 year old paint on the display lens didn't survive kapton tape :/

So the kapton tape peeled the paint off?
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Offline lukier

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Re: Restoration glory of Keithley 2001 DMM
« Reply #629 on: November 03, 2016, 09:22:32 am »
Why? Not fitting well... made in China crap?

No, different routing of pins and AFAIR TL866 software doesn't support 27C4096 in PLCC44 packages, just DIP40. So to mimick DIP40 one needs adapter like this:

http://www.ebay.co.uk/itm/111553438268

So the kapton tape peeled the paint off?

Yup. Maybe I should've ignored that and just apply peroxide without worrying about the paint. I think the display lens can be removed entirely as well.
 
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Online zucca

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Re: Restoration glory of Keithley 2001 DMM
« Reply #630 on: November 03, 2016, 09:57:05 am »
Ok, getting ready for my sick puppy.

Tamiya Extra Thin Cement - Ordered
12% Peroxide - Ordered

It will be a long journey... my K2001 was used in Canada to monitor the liquid temperature in a wine production process. It passed all the self checks... but there will be some surprise inside... if only my day would have 48 hours...

I think the display lens can be removed entirely as well.


I´ll try that... like macboy did

https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg937701/#msg937701

« Last Edit: November 03, 2016, 10:32:22 am by zucca »
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Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #631 on: November 03, 2016, 01:18:45 pm »
So yesterday I was testing my new DB62 decade resistor and after many hours of switching and tests I found it maybe still in spec.
It was a maybe because I wasn't able to test the 100K Ohm and 1M Ohm with my K2001.

After two years of using it I found repair job I made two years ago wasn't complete because it still has a problem with high range resistance measurements. The problem seems affecting all Ohm ranges, but it became significant at 200K Ohm range, getting worse at 2M ohm, culminating with almost not working at 20M, 200M and G Ohm.

I noticed multimeter was out of specs in some Ohm ranges one year ago when I was testing my 100K Ohm 0.005% Vishay "standard resistor", but because I really never used this high Ohm ranges I never had a chance to realise it was so bad.

Initial diagnosis:

  - seems not a leakage problem, in G Ohm I can read OL
  - self test always passes with no error

First things to do is check current source circuit and all relevant analogue switching stuff. Most probably is one switch gone bad.
Actually digging in schematics and self test description ... to get a clue how Ohm measurement circuits works.
Seems I win a new repair for free.
« Last Edit: November 03, 2016, 01:20:31 pm by mimmus78 »
 

Online zucca

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Re: Restoration glory of Keithley 2001 DMM
« Reply #632 on: November 03, 2016, 01:24:21 pm »
mimmus78, self tests no problems right?

And with these the calibration failed! Error 385, 20 MOhm 2W gain out of spec. High ohm resistors are a nuisance so I figured out that my soldering spree panic on the analog board left a mess affecting ohms current sources. After cleaning everything under a microscope, every guard trace, resistor cases, with dozens of cotton swabs and isopropanol the calibration worked!  :-+ I could even measure 1GOhm resistor.

is your board clean?
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Offline Alex Nikitin

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Re: Restoration glory of Keithley 2001 DMM
« Reply #633 on: November 03, 2016, 01:42:13 pm »
Initial diagnosis:

  - seems not a leakage problem, in G Ohm I can read OL
  - self test always passes with no error

First things to do is check current source circuit and all relevant analogue switching stuff. Most probably is one switch gone bad.


I would first check the input current on DC Volts (10V and below) - leaky JFETs (protection and switching) would create a problem on DCV and OHM inputs.

Cheers

Alex
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #634 on: November 03, 2016, 03:16:11 pm »
>> is your board clean?
>> I would first check the input current on DC Volts (10V and below) - leaky JFETs (protection and switching) would create a problem on DCV and OHM inputs.

I did a small repair on this meter, one analogue switch involved in current measurement was half working. The culprit was found on 20 minutes investigation, the component easily replaced and all cleaned with IPA.
I'm sure I didn't contaminated it, but who knows what did previous owner!?

I remember there was also a bodged mod on some JFET (Q550) that probably was made by previous owner. I posted a photo here few years ago of this bodge, but at this time there wasn't public available schematics so I wasn't able to speculate for what it was done.
Maybe it is some goofy attempt to repair the meter made by by previous owner for the same failure I fixed.

I can see some noise starting at 10K and it really show up at 100K, don't think contamination can have this high effect at this "low" Ohm levels.
10V is 11PPM away from another K2000 since two years. Noise at 10V is as specs and comparable with noise of other K2001s owned by other members here.
I used 100mV some time but I do not remember problems there.

Think I have enough stuff to work out for now ... and as usual any suggestion is appreciated.
I'll keep you all "K2001 aficionados" updated.
« Last Edit: November 03, 2016, 06:54:14 pm by mimmus78 »
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #635 on: November 03, 2016, 08:29:52 pm »
So this the bodge ... I checked with microscope and I can see some glue on the wire. At least it's seems some "definite" modification and not a temporary attempt.

Also 100mV range is clean.



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« Last Edit: November 03, 2016, 08:36:29 pm by mimmus78 »
 

Offline lukier

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Re: Restoration glory of Keithley 2001 DMM
« Reply #636 on: November 05, 2016, 02:23:14 pm »
I got my meter warmed up, so I've decided to measure the Ohms current sources. Maybe someone will find that useful or other users with more reliable K2001's than my still-uncertain-recently-repaired one can provide their own data.

I've used Keithley 485 Picoammeter for all ranges except 20 Ohm, where it is out of range of K485 so I've used 3457A in the current range.

Ohms RangesCurrent
20 Ohm~ 9mA
200 Ohm, 2 KOhm0.981 mA
20 kOhm89.3 uA
200 kOhm7.09 uA
2 MOhm772.7 nA
20 MOhm70.72 nA
200 MOhm, 1 GOhm4.394 nA

Keithley 2001-TCSCAN manual, in the calibration section (page 4-10) mentions that on the 200 kOhm range the sourcing current is 7 uA, so at least in this range my meter seems OK.

I've tried to measure the input bias current on the DC Volts low ranges, but it is well below my K485 sensitivity and measurement setup (BNC cable with a BNC to Banana adapter, no triax). Similary, I've tried connecting 1 GOhm resistor to K2001 on the DC range (200 mV) and the readings are just jumping around between -70 mV to +20 mV.  :-//
« Last Edit: November 05, 2016, 11:00:03 pm by lukier »
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #637 on: November 05, 2016, 10:22:24 pm »
So situation kinda getting worse.

Now self test always give me errors 304.6 and 306.7.

Sometimes also lower tests up to 304.3 give me some errors, but this depends on humour of the multimeter (maybe some part gets hot).

I figured out I have some leakage somewhere, here is what I found when running test 304.3.



This error give me just time to take a note because now 304.3, 304.4, 304.5 are working again.

So I made some analysing the circuit and I was almost sure my leakage was caused by one of this Q320, Q312 or Q324.

I removed all three fets, replaced Q324 with a 30ohm resistor between source and drain and by running test 304.6 I demonstrated I was wrong and leakage is still there.

Will continue investigation tomorrow ... if anyone have any idea how to solve this puzzle, I will appreciate.

Domenico

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Offline plesa

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Re: Restoration glory of Keithley 2001 DMM
« Reply #638 on: November 05, 2016, 10:29:11 pm »
I propose replace shift registers 14094 and all analog switches (DG411/DG404/DG211). It is much faster than troubleshooting these failures.
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #639 on: November 05, 2016, 11:40:23 pm »
Yes plesa: I'm starting thinking to brute force attack too ...

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Offline plesa

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Re: Restoration glory of Keithley 2001 DMM
« Reply #640 on: November 05, 2016, 11:45:51 pm »
Yes plesa: I'm starting thinking to brute force attack too ...

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It is not brute attack, the components are cheap and it is more efficient to replace them all. It is difficult to find where leakage is.
Keithley also repair multimeters this way. They will replace few components and in case it does not help you will receive discount on new meter :)
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #641 on: November 06, 2016, 08:09:16 pm »
Gotcha! Test 304.6 was ok without U325 ... little bastard!

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Offline plesa

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Re: Restoration glory of Keithley 2001 DMM
« Reply #642 on: November 06, 2016, 08:48:29 pm »
Gotcha! Test 304.6 was ok without U325 ... little bastard!

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Replace them all, it is really worthwhile. It needs to be calibrate again anyway.
 

Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #643 on: November 06, 2016, 08:55:05 pm »
Seems nobody in Europe has stock!
Ebay or get from USA?
 

Offline plesa

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Re: Restoration glory of Keithley 2001 DMM
« Reply #644 on: November 06, 2016, 09:15:07 pm »
Seems nobody in Europe has stock!
Ebay or get from USA?
wait what you want to replace?
DG411 and shift register MC14052 Farnell has on stock.
If you needs something special drop me PM, I will check my local inventory for Keithley repairs :)
 

Offline lukier

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Offline mimmus78

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Re: Restoration glory of Keithley 2001 DMM
« Reply #646 on: November 06, 2016, 09:43:47 pm »
I need MC14052BCP in DIP 16 package.

It was not ROHS part, so nobody use here Europe anymore.

I asked some eBay guy if he is sure parts he sells is genuine ... let see tomorrow what will reply.

Anyway if you have this part, we can arrange something.

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Offline Kleinstein

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Re: Restoration glory of Keithley 2001 DMM
« Reply #647 on: November 06, 2016, 09:57:33 pm »
You could likely get away with an CD4052B part. It might be slightly different parameters but most of them overlap and speed should not really matter.  This one is available, e.g from tme.eu.

One might have to select for low leakage samples: typical values are good, but worst case performance is likely not good enough.
 

Offline plesa

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Re: Restoration glory of Keithley 2001 DMM
« Reply #648 on: November 06, 2016, 10:02:11 pm »
I need MC14052BCP in DIP 16 package.

It was not ROHS part, so nobody use here Europe anymore.

I asked some eBay guy if he is sure parts he sells is genuine ... let see tomorrow what will reply.

Anyway if you have this part, we can arrange something.

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http://se.farnell.com/texas-instruments/cd4052be/ic-mux-demux-4ch-4052/dp/9589538
 

Online 2N3055

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Re: Restoration glory of Keithley 2001 DMM
« Reply #649 on: November 06, 2016, 10:48:35 pm »
RS has CD4052BEE4 ... RS cat no : 121-9243

it might have a bit better leakage... they are cheap, maybe buy few and sort the best ones...
 


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