This Keithley 2001 IS NOW saved!

[Zucca]

The previous owner did not care too much, he deserve a middle finger  ...





I want to save this sick device!

What I did:

1) Replaces all leaking and not caps. Yeah they did leak but not soo much... board cleaned and it was not corroded.
2) Fan replaced (just becaused it was cheap)
3) the poor tortured U629 was replaced with a new one and put back in the original location.
4) The missing R100 was installed with a similar model... the cement one was too expensive.
5) Zip tied the big blue capacitor C611 15000µF closed to U629

Now I got the following errors:

404.1 – Absolute value (x1 gain); -full-scale DAC output
404.2 – Absolute value (x1 gain); -half scale DAC output
404.3 – Absolute value (x1 gain); zero DAC output
404.4 – Absolute value (x1 gain); +half-scale DAC output
404.5 – Absolute value (x1 gain); +full-scale DAC output

405.2 – Absolute value x10 gain comparison; large +DAC output
405.4 – Absolute value x10 gain comparison; small +DAC output

406.6 – Voltage comparison

407.1 – Front end; 2V range
407.2 – Front end; 200V range
407.3 – Front end; 750V range

412.1 – AC amps switch

This is just the first post, now I will start the investigation.

[Zucca]

Power supply check ok. The only thing somehow strange was

U103, pin 3: 22,3V (~+18V in the manual)
U103, pin 2: 7,89V (+8V in the manual)

but I will not consider it as a defect.

Now with the unit warmed up I got these errors as well in addition to the others before:

405.6 – Absolute value x10 gain comparison; small –DAC output
405.8 – Absolute value x10 gain comparison; large –DAC output

410.1 – True RMS converter

411.1 – Filter; true RMS
411.2 – Filter; true RMS

 

[TiN]

Check booster power stage and stuff around dual JFETs U5** , if my memory still serve me well.

[Kjelt]

Did you recap all the electrolytics ?
Better do it before you really get a mess.

[Zucca]

Did you recap all the electrolytics ?
Better do it before you really get a mess.

oh yes read above point 1).

What I did:

1) Replaces all leaking and not caps. Yeah they did leak but not soo much... board cleaned and it was not corroded.

I opened up the unit and fond some elco pee, it just started leacking.
I did not power up the unit and replaced and cleaned everything like a good EE boy.

[Zucca]

https://xdevs.com/fix/kei2001/
https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/

Did some homework with the excellent TiN article and previous posts:

If you have many 4xx.x series errors check U520 and U525. These op-amps have floating power and can be damaged from bad capacitors in doubled voltage supply.

[...]

Many 4xx.x tests we failing in self-diagnostics.

After few days of troubleshooting culprit was found in Linear Systems U441 dual JFET pair in floating FE circuitry, causing current mirror to become unleveled and failing all related tests and operation. U520 had incorrect drive due to one of JFETs in Q512 gone bad.

will check it.

Desolder U507, U508, U509 and clean surface/pads in this area with clean acetone. After cleaning – solder U507,U509 back, and replace U508 to new 74LS00 as it’s just jellybean part and easier to put new in, than testing if original is ok.

Mine were in contamination for about 12-14 hours, I cleaned them well and they look good... I pospone this.

https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg727146/#msg727146

The failed component was Q547 - it wasn't totally open but but didn't turn on properly so relay K503 never closed.

https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg762210/#msg762210

Q518 was shot, IMHO because K503 was stuck closed before.

will check


PS: If you need the Service stuff, look here:
https://cal.equipment/doc/Keithley/2001M/CDROM/Model%202001%20Repair%20Manuals/
at https://xdevs.com/ the links do not work anymore.

 

[Zucca]

TO DO List after repair:

1) New Front Panel (Assembly or not?)
2) Missing Bolt at rear coax input, those are important to keep the analog board in place. where I can find them with washer?
3) MEM2 update with DS1245Y or for the future:

https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg956554/#msg956554

4) FW Upgrade

OPTIONAL

1) µV Meter option

[Kjelt]

I got stuck with an ADC selftest error while the meter itself works flawlessly.
The problem is probably somewhere a single corroded pcb trace perhaps inside layer that is high ohmish.
The ADC draws current during selftest and then the voltage drops.
Can not find the culprit, I like Keithley very much but the way they overcrowded this pcb with its tiny electrolytes stuffed against the very hot voltage regulators made me rethink if I like them really that much.
So lessons learned, really spent time to see if the traces are clean and you don't have any corrosion inside the pcb.

I do hope your patient on your table is in better condition than mine and you will get it to work 100% 

[Zucca]

I got stuck with an ADC selftest error while the meter itself works flawlessly.
The problem is probably somewhere a single corroded pcb trace perhaps inside layer that is high ohmish.
The ADC draws current during selftest and then the voltage drops.
Can not find the culprit, I like Keithley very much but the way they overcrowded this pcb with its tiny electrolytes stuffed against the very hot voltage regulators made me rethink if I like them really that much.
So lessons learned, really spent time to see if the traces are clean and you don't have any corrosion inside the pcb.

I do hope your patient on your table is in better condition than mine and you will get it to work 100% 

Put it on the bench again, we will fix it together.
Yes the Keithely EE did some sloppy job somewhere in the K2001. That's why the EEVblog EE are here to help.

[Kjelt]

Put it on the bench again, we will fix it together.
Yes the Keithely EE did some sloppy job somewhere in the K2001. That's why the EEVblog EE are here to help.

  I have my patient put in another EE hospital with a doctor that has about 20 years more repair and faultfinding experience than I do 
He has it as a pet project spending a few hours here and there.
The nice thing about the Keithleys is that the service manuals and schematics are often available, perhaps not 100% complete but still thanks to TiN for a larger part.

[Zucca]

Test 400.1 – DAC; -4.21V output

The TRIG bits for OUT B of the DAC (U531) are programmed to produce -4.21V at PRECOM+
(pin 1 of U528). This signal is routed through R560 and U532 (DAC line pulled
low). This line, now called ACF, is selected by multiplexer U511. The output (OUT) of
the multiplexer is routed through buffer U342 and resistor R223 (where the line is
called ACV/A). The signal on ACV/A is then routed through U320 (/AC pulled low)
and applied to Op Amp U322. Measure -4.21v at A/D IN.

this passes.

This 404.1 fails:

Test 404.1 – Absolute value (x1 gain); -full-scale DAC output

DAC U531 is programmed to generate -4.21 VDC at PRECOMP+. That signal is then
applied to ACF through R560 and U532 (DAC line pulled low). ACF is routed to AMP
IN via U526, Q516, and the AC input buffer.
AMP IN is tied to the inverting and non-inverting paths of the variable gain ampliÞer
(VGA). NETOUT (output of U519) is routed to the Zero-Crossing AmpliÞer which,
based on the polarity, generates the appropriate COMP- signal that is applied to comparator
U507. The comparator selects the path that the AMP IN signal will follow
through the VGA by closing the appropriate analog switches of U509.
The negative (inverting) AMP IN path is through R530, U515, U509, Q501, and U516 to
pin 12 of the multiplexer (U511). The output (OUT) of the multiplexer is routed
through buffer U342 to ACV/A. The signal on ACV/A is switched through U320 (/AC
pulled low) to the A/D buffer (U322) which is conÞgured for x1 gain. Measure +4.21V
at A/D IN.

the circle is getting smaller.

[Zucca]

U509 is mentioned in all the failing tests and only there.
We have a high suspect component.

Next move is to listen to TiN advise and

Desolder U507, U508, U509 and clean surface/pads in this area with clean acetone.

 

[Kjelt]

But do you use acetone or IPA, I am afraid that acetone could remove the silkscreen ?

[Zucca]

IPA should be enough... silkscreen ist partially already gone.. do not care too much.

[Zucca]

Under U507, U508, U509 there was some junk and I cleaned everything up.

Unfortunately nothing changed.

Time to dig more into the problem.

[Kleinstein]

IPA should be enough... silkscreen ist partially already gone.. do not care too much.

For cleaning things like leaking electrolyte water may be a better solvent than IPA. So it can be a good ideal to start with water or at least a water IPA mixture. Pure IPA or methanol would be than the last step.

[Zucca]

Thanks Kleinstein, I did wash the chips with IPA and water. On the boardI used IPA to remove the tacky flux and whatever was there. At the end it looked very clean.

Anyway tonight one step back.... maybe.

I powered off the unit to look for a good A ground with a 34461A so I could poke around for the signals...
Guess what... I powered the unit back and got these new errors:

400.1, 2, 4, 5

and they stayed there no matter what I did.

So back to the schematics and here what I found while running 400.1 (schematic 2001-902-06.pdf page 4)



R560 is connected correctly and I measure 10KOhm betweem PRECOMP+ and U532 pin2.
There is too much current flowing through R560 causing the big voltage drop.

Are those DG411 and DG211 started to leak right now?

Time to listed to plesa:

https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/msg1064632/#msg1064632

I propose replace shift registers 14094 and all analog switches (DG411/DG404/DG211). It is much faster than troubleshooting these failures.

[TiN]

OPTIONAL

1) µV Meter option

Only if your meter has B-type firmware (2 ROMs) and you don't mind spending $1K+ for amplifier setup.

[Zucca]

Only if your meter has B-type firmware (2 ROMs) and you don't mind spending $1K+ for amplifier setup.

B-type 2 (ROMs) is there. That said I am very happy it's just an option for me, I do not really need a µV.
Anyway much cheaper than many others µVmeters out there.
Thanks you again TiN for all your effort to document your fixings.

[Zucca]

Coming next...

IC, CMOS ANAL. SWITCH, DG411DY(SOIC)
VISHAY DG-411DY-E3

U317
U522

2 Qty

IC,CMOS ANALOG SWITCH DG211DY(SOIC)
VISHAY DG211BDY-E3
 
U510,U515,532
U318-320,323

7 Qty

and if they are in stock and cheap:

IC, CMOS ANAL SWITCH, DG444DY, (SOIC)
VISHAY DG444DY-T1-E3

U526

1 Qty

IC, 8 STAGE SHIFT/STORE,MC14094BD(SOIC)
ON SEMI MC14094BDR2G

U500,501,505,530
U800,801
U300,302,303,305,307

11 Qty

IC, MCHAN LAT DMOS QUAD FET, SD5400CY (SOIC)
Unknow in Manual

U509

1 Qty

IC, QUAD 2-INPUT NAND, 74HC00M (SOIC)
Unknow in Manual

U508,513,536

3 Qty

[Zucca]

DG411 can be upgraded to:

https://www.mouser.de/datasheet/2/256/maxim%20integrated%20products_dg411-dg413-1178575.pdf

same with DG444

https://datasheets.maximintegrated.com/en/ds/DG444-DG445.pdf

Bonus: same with DG408

https://datasheets.maximintegrated.com/en/ds/DG408-DG409.pdf

[Kleinstein]

Those old CMOS switches somehow seem to be prone to failure.

Not many of the switches are really critical and need very low leakage or resistance matching.
The new chips are usually DG2xxB and thus already an upgrade to the old version without the B.

[Zucca]

Those old CMOS switches somehow seem to be prone to failure.

Not many of the switches are really critical and need very low leakage or resistance matching.
The new chips are usually DG2xxB and thus already an upgrade to the old version without the B.

Correct but I could not find the B version of DG411, DG444, DG408 and I went to Maxim.

[Zucca]

if nobody has a better plan I will order tonight.

[Kleinstein]

For the switches in the AC part, I would be careful with an "upgrade", as for these switches the capacitance can be more important than leakage. So changing the switches would likely need a new low level Cal / adjustment for the AC part.
Also many of the other switches are not with high impedance parts and not that critical. So no need for the more expensive Maxim parts. It looks like the really critical signals are switched with JFETs anyway.

AFIAK most of the DG4xx are new chips and thus no separate old and B version.