Author Topic: Restoration glory of Keithley 2001 DMM  (Read 212778 times)

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Online Kleinstein

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Re: Restoration glory of Keithley 2001 DMM
« Reply #725 on: March 03, 2019, 09:59:01 am »
I also see the "charge pump" used to move the 7 V reference to a different reference point - this about the only part I like about this implementation.  U331 is just a buffer for this shifted 7 V reference for less demanding use (e.g. bootstrapping the protection and gate drive).

The Ohms current source is in deed confusing. As far as I understood it they use the opto-coupler U537 in analog mode for the current regulation loop with the higher current ranges. U324 does the loop control.

U333 seems to be the regulating amplifier for the very low current source (Hi_ohm). There is a separate current source for the lowest current, that used R354 as it's reference resistor.
 

Offline ddcc

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Re: Restoration glory of Keithley 2001 DMM
« Reply #726 on: March 04, 2019, 07:35:59 am »
2.4 Hz pulses are probably from autozero.  Switch it off to check.

You're right, they do go away when I disable autozero.

The Ohms current source is in deed confusing. As far as I understood it they use the opto-coupler U537 in analog mode for the current regulation loop with the higher current ranges. U324 does the loop control.

U333 seems to be the regulating amplifier for the very low current source (Hi_ohm). There is a separate current source for the lowest current, that used R354 as it's reference resistor.

Thanks for all the information, it's starting to make more sense now. Yeah, the manual mentions that the current source for the mega/gigaohm ranges uses R354 through OHM ISOURCE, instead of the regular OHMS path through the K300 relay and protection circuit.

I've managed to repair the unit, but it wasn't very satisfying. I ended up connecting a logic analyzer to A/D IN, A/D_DATA, D_OUT, R1_STB, R2_STB, and DC_STB, in order to figure out what the unit was doing/measuring in the open circuit calibration phase that was failing, since the manual provides the full bit patterns for the shift registers. I happened to do a four-wire resistance calibration this time, instead of a two-wire resistance calibration, as I had previously gotten lazy trying to reproduce the problem, since it only happened on the last phase of comprehensive calibration. This time, the calibration succeeded with no errors, so I removed my logic analyzer/probes and re-attempted calibration, which again succeeded, so I fully re-assembled the unit and finally performed actual calibration. I can only surmise that perhaps the fault was indeed in one of the analog switches, which I fixed when I replaced them, but didn't notice because I got sloppy with the calibration.
« Last Edit: March 04, 2019, 07:37:50 am by ddcc »
 

Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #727 on: March 04, 2019, 10:30:13 am »
Also keep in mind that you need to perform "manufacturing" low level calibration to do actual adjustment for current and ACV/ACI functions. If current reading is not correct than comprehensive user calibration will still give you out of spec adjustments.
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Offline ddcc

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Re: Restoration glory of Keithley 2001 DMM
« Reply #728 on: March 04, 2019, 02:50:31 pm »
Thanks for mentioning it. I'd like to, but I don't have the capability or calibrated gear for that step. Luckily, it's fairly accurate when I check against a DMMCheck.
 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #729 on: March 20, 2019, 09:05:49 am »
Still busy cleaning  :( , take it slowly, half hour here and there. The nwe caps arrived.

Now my first thought was to also clean the via's through and through, place a thin wire and resolder.
I find it very hard to clean the smaller via's, they also stink awfull like cat-pee. I wonder are these via's closed ?

Anyone that did this cleaning have additional tips for the via's ?
 

Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #730 on: March 20, 2019, 12:16:13 pm »
Must clean very thorough to make smell go away.
Via's usually not closed but sometimes clogged with soldermask/solder. When I was fixing vias i used tinned strand from wire small enough to fit via, heat via from other side with iron and push strand thru.
Then solder both ends and repeat procedure for all vias under affected corroded area.
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Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #731 on: March 20, 2019, 12:17:24 pm »
Ok wow, so how many hours did you spent on your repair in total ?
 

Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #732 on: March 20, 2019, 12:27:26 pm »
Actual repair took not that long. It was more of a learning process. I sold/traded all 2001's long ago tho.
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Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #733 on: March 28, 2019, 07:07:17 pm »
Well it is alive  :-+
Not fully 100% though, get adc errors.
What is strange is that it seems to work, 10V on the inputs looks ok.

Read the manuals tomorrow to see what is going on.
 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #734 on: March 28, 2019, 10:49:30 pm »
Reading this topic the errors will probably be gone if I update the firmware from A05 to A08 correct ?

Looking at my digital board it does not match the schematics of the xdev site.
I seem to have two proms with a sticker A05, one in a socket (U611) and one (U618) soldered to the board, also only one 512kB ROM file on xdev so what is up with that ?
Is there a flash compatible chip just like with the 2000 I can get ?
 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #735 on: March 29, 2019, 12:04:52 am »
Ah stripped the sticker from the socketed eeprom and it is a HN27C4096CC-15 which is a 16 bit eprom, so that clears that up  :)
I do have a few ST M27C4002, they look like pin compatible.  :-+
 

Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #736 on: March 29, 2019, 05:00:38 am »
Quote
Reading this topic the errors will probably be gone if I update the firmware from A05 to A08 correct ?
No, those are rather horrid errors, firmware is not a problem.

If you have two PROM digital board, you got lucky and should install B-version firmware , like B15.
I mean for you probably does not matter, but B-firmware allow use of Keithley 1801 in scanner slot.

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Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #737 on: March 29, 2019, 12:20:22 pm »
Hi TiN first of all again many thanks for all your hard work on xdev and help here, really appreciate it  :-+
To get back to your answer:

No, those are rather horrid errors, firmware is not a problem.

I would also think so but if you look at the history in this topic it looks different:

- You had a long session with SKE from page 18 onwards he had exactly the same errors without a final solution
- Then Kada had the same errors from post https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg880823/#msg880823
forward. No solution.

Then this post came and SKE and kada say that firmware upgrade solved the 200.x and 201.2 errors.


SKE encountered with the same errors:
Self test reported these error codes:
200.1   A/D Zero
200.6   x0.02 Line Cycle Integration
200.7   x0.01 Line Cycle Integration
201.2   7V Reference
Did you find a solution?

I'm sorry for delayed report, the solution (TiN, you was right  :-+) was to update firmware to A08 and I don't have these errors anymore.

Now I have absolutely no clue why this would solve the issue, perhaps the new firmware overwrites or rewrites the calibration eeprom?
I will make backup of the eeprom first.
But I guess it can't hurt to try it ?

What's your opinion?



 

Offline TheSteve

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Re: Restoration glory of Keithley 2001 DMM
« Reply #738 on: March 29, 2019, 04:42:44 pm »
Backup the cal eeprom data and update the firmware.
VE7FM
 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #739 on: March 29, 2019, 06:13:17 pm »
Backup the cal eeprom data and update the firmware.
First done
Second have to do the little to big endian conversion of the rom.
 

Offline TheSteve

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Re: Restoration glory of Keithley 2001 DMM
« Reply #740 on: March 29, 2019, 06:29:48 pm »
If you had firmware A05 shouldn't you be installing A08, which I believe is a single file and should directly program into your eprom.
VE7FM
 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #741 on: March 29, 2019, 06:58:14 pm »
Correct but TiN put the rom files as little endian, it needs to be converted to big endian, he has a python script for it, so will need to do that first.
 

Offline openloop

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Re: Restoration glory of Keithley 2001 DMM
« Reply #742 on: March 30, 2019, 01:31:47 am »
Kjelt, I doubt that it has anything to do with firmware.

What are the symptoms? (apart from test errors I mean)
Does the unit make correct measurements in 20v and 2v ranges? Both with applied voltages and shorted?
Does the self test complain the same if you let the unit warm-up for an hour?
Do the proper voltages make it to ADC board when you step through diagnostic patterns? (e.g. 7v, 7v*1.5, 0v, signal, etc.)


 

Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #743 on: March 30, 2019, 09:11:41 am »
Yes DCV is ok and on par with my K2000.
7V is on ADC in after test and the other I believe 1,75V test passes so ADC is ok.

What I don't like is that some parts of the analogue board (beside the regulators) heat up to 40-45C within seconds, is that normal? Many small parts on the bottom of the pcb so can't see which ones exactly.
Does anyone have a thermal image of their analog board ?
 

Offline openloop

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Re: Restoration glory of Keithley 2001 DMM
« Reply #744 on: March 30, 2019, 01:11:57 pm »
Quote
7V is on ADC in after test and the other I believe 1,75V test passes so ADC is ok.

Actually it does not mean that. Even if ADC is wonky (but not crazy), autozero can calibrate the wonky out and show more or less correct values.

The difference between test 200.1 and regular measurement is that 200.1 is checking absolute charge-discharge count, but regular measurement is relative to references.

Easy to check.
Short inputs, connect your scope between signal zero ("S COM" on ADC header) and integrator' output (pin 6 of U809 DIP), set range to 20V (for orange-to-orange comparison), turn off autozero (to reduce clutter), and compare scope's traces of ADC's dual slope phase to attached screen shots.
And by compare I mean really compare - dc offset, charge slopes, discharge slopes - everything. Test 200.1 simply counts number of clock ticks (you checked the quartz to be 7.68 MHz right?)  corresponding to charge and discharge periods and compares it to a pre-programmed constant. Of course that constant might be corrupted - then new firmware might help.

 

Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #745 on: March 31, 2019, 03:14:17 am »
Does anyone have a thermal image of their analog board ?

My 2001 notes article have plenty of IR photos on 2001. They do like to get bit toasty  ^-^.
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Online Kjelt

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Re: Restoration glory of Keithley 2001 DMM
« Reply #746 on: March 31, 2019, 09:07:28 am »
Does anyone have a thermal image of their analog board ?
My 2001 notes article have plenty of IR photos on 2001. They do like to get bit toasty  ^-^.
No wonder the caps were toast.
Too bad the caps leak instead of dry up. :)
 

Offline eplpwr

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Line sync sketchy
« Reply #747 on: April 15, 2019, 07:10:01 am »
Hi!

Recently I got a 2001 in good condition. The meter works great, except for one thing: When I enable Line Syncronization (followed by TRIG button) the display updates become sketchy and for long times the display just shows "---------" [VDC/ADC/Ohms/whatever]. So, it seems there is at problem with the mains zero-crossing detection (or whatever method is used to sync to mains). The L-S problem was present when I received the meter, but I have no complaints as it was really cheap - sold as Parts.

This is what I've done to the meter, after receiving it:
- Replaced all electrolytic capacitors on both analog and digital board. The "old" ones had 2008 datecodes and did not show any signs of leaking.
- Upgraded firmware to B17/2001M. Unit was received with B16 firmware (now uploaded to xdevs.com).
- Upgraded from plain SRAM (no MEM option) to MEM2 (DS1245Y). Initialized NVRAM from Secret menu - working good.

I have the Repair manuals, complete with schematics, but I have trouble understanding which net is used for Line Sync.

Self-test passes all tests with no errors.

Is there some obvious solution to my problem that I've overlooked?
 
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Offline TiN

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Re: Restoration glory of Keithley 2001 DMM
« Reply #748 on: April 15, 2019, 11:57:49 am »
Thanks for firmware!

Does your unit pass all self-test in continuous loop  for few hours? Sometimes there is random error due to bad optocouplers between analog/digital, that cause "locks/freezes" like you describe.
What if you gently smack unit on the side, do the readings change (freeze up/reset/etc)? Line sync is FREQ signal that goes into A/D board, so you can trace from there.

Pics would be nice to see, sounds like your meter rather recent.
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Offline eplpwr

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Re: Restoration glory of Keithley 2001 DMM
« Reply #749 on: April 15, 2019, 08:34:37 pm »
Does your unit pass all self-test in continuous loop  for few hours? Sometimes there is random error due to bad optocouplers between analog/digital, that cause "locks/freezes" like you describe.
What if you gently smack unit on the side, do the readings change (freeze up/reset/etc)? Line sync is FREQ signal that goes into A/D board, so you can trace from there.

Pics would be nice to see, sounds like your meter rather recent.

Hi TiN!

It seems I can run self-test for several hours without any errors. I didn't think of "smacking" the unit, but after trying that there is definitely somethings going on: after enabling line sync, I get a reading every 10-15 seconds (conversion speed "normal" - default). Between the readings "---------" is shown in display. If I bump the meter (not too hard  :D ) I can unfreeze the meter to get a few readings before meter goes back to "--------" display. So my "average # of readings per minute" goes up when bumping the meter. Something electro-mechanical seems to be going on - just have to figure out exactly what's happening.

An observation: When changing to Line Sync, there is always a number of initial readings for 2-4s after pressing the TRIG button. It's almost like some capacitor was fully charged and then drained of energy, only to be recharged each 10-15s to get a few more readings, before being emptied of charge, again. This is a long shot, I know...

I have to disassemble to meter again to be able to probe the connectors to the A/D board - FREQ specifically.
 


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