Author Topic: Keithley 2001 DVM factory modifications to work with a K1801 nanovolt preamp  (Read 35453 times)

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Online chuckb

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I tried to get a factory manual after I got the voltmeter but none were available. I must have a power supply problem because my voltages are not symmetrical. I'll have to research that. Thanks

chuckb - I have a N1a Service Manual from Ernest J. Moorey, but can't find any information about batteries. The measured voltage is 9-10 V.
 

Online chuckb

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The N2a Nanovoltmeter looks very similar inside.
 

Online chuckb

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The continuing story of starting with just a K1801 preamp and assembling a complete system. Tonight - The interconnect cable, well one end of it.
TiN was correct it's an 8 pin RJ50 style connector. I used PN 520424-3 to work with the 24 ga wire in the unshielded CAT 5 cable that I had handy.

The correct tool and die to crimp this connector cost about $10,000 with a several week lead time. That price seems reasonable, ;) however the lead time was an issue for me. So I used a screwdriver that I had on the bench. The screwdriver blade is 0.215" wide and 0.030" thick. It could have been slightly less thick. I inserted the 8 wires, lined the screwdriver up with the first gold contact and thumped the handle a few times. Repeat 7 more times.

After I was finished I read the connector assembly documentation. It turns out I over thumped the contacts. When correctly positioned the contacts should be 0.270 +-0.003" above the back side of the connector. My contacts were 0.250", oops. The continuity is good even as I move the connector so just be careful if you try the screw driver assembly method. That what I get for not waiting a few weeks for the correct tool.

I finished assembling the connector with two metal shields and the rubber boot. It ended up looking very good. I could have used shielded wire but my A10 does not pick up noise on the output wires so I was not to worried about this cable.

Digikey has all the parts in stock.


 

Online chuckb

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Corrected the connector part number on this photo
 

Offline TiN

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Screw-crimping :) Was there, did that.

Since I don't think getting 600$-worth transformers is an option for many, here's proposed battery powered low-noise LDO supply, using pair Linear LT3042 (200mA, 0.8uV noise spec).



As chuckb mentioned, care should be taken to connect isolated supplies, since both LDOs are positive. Will see how it work.

LTSpice circuit

I took measurements of scan card and created keepout zone for out future preamp board :



Test board for power:

« Last Edit: October 15, 2015, 04:31:20 am by TiN »
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Online chuckb

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That regulator looks great! We might need provisions for an electrolytic on the input to dampen long lead wires to a battery. I see there is an MSOP package available, that might be easier to solder to.
 

Online chuckb

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Testing I2C EEPROM with PREAMP config on addon port with K2001 B17:

[
:)

I hacked an EEPROM onto a connector and got the preamp mode working also! Pin 13 needs to go to 5v as a CARD Detect signal for the processor.
I manually Calibrated the gain for the G=1k, G=10k ranges. They worked just fine. The meter would not accept the manual setting for the G=100k range. I could change the value but when I exited the mode it went back to a gain calibration of 1. It was very strange. Does it work on other meters?
 

Offline TiN

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I'll have to check. I tried yesterday pin13 trick, but prolly data in EEPROM did not play well, as on next power on meter detected card, but it showed it as usual scanner card, not a preamp, even tho I did "init" thru secret menu.
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Offline TiN

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Digital side of preamp supply card is routed  ;)
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Offline TiN

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PCB for K1801 preamp head in the works, not forgotten.

Digital section done, LDO section almost done. Hope to complete this week.  :-/O
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Online lukier

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I was going through various patents and came across this one:

https://data.epo.org/publication-server/pdf-document/EP14170592NWA1.pdf?PN=EP2809004%20EP%202809004&iDocId=7873105&iepatch=.pdf
(EP2809004)

I'm following this thread and I thought it might be of interest to the other forum members.

It seems that the HP 3458A ADC designer, now working for Keithley, is recently busy with nanovolt measurements :)
 

Online chuckb

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PCB for K1801 preamp head in the works, not forgotten.

Digital section done, LDO section almost done. Hope to complete this week.  :-/O

The board looks great!
 

Offline ManateeMafia

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Yes it does.

When you finish the layout and test the board, it would be great to discuss any layout strategies used in the design for newbies like myself.
 

Offline TiN

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You? Newbie? I smiled, that's good one. :-+

I plan to have article-worklog eventually, covering both layout, schematics and usage.
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Online zucca

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newbies like myself.

You? Newbie? I smiled, that's good one. :-+

Eh eh, and what I should be? Anyway I believe this project will be a kiss ass one. I am available to split the cost of prototyping of whatever, just PM me.
« Last Edit: October 27, 2015, 02:25:34 pm by zucca »
Can't know what you don't love. St. Augustine
Can't love what you don't know. Zucca
 

Offline TiN

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Attached animated GIF of finished boardie  8)
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Offline ltz2000

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The Keithley 1801 is an EM Electronics A10 made to order for Keithley.

The layout of the Keithley 1801 posted by chuckb is a direct copy of the EM A10 old version. His A10 in the same photo seems to be a later layout.

Please, please, do post inner photo and better external photos of preamp.

Many years ago I got a badly damaged A10 amplifier and did some reverse engineering. Including the potted mu metal box, which was a real pain in the ass to open. I hope I can still find the documents. I don't promise that they are complete or correct, but it shouldn't be that difficult to fill in the gaps.
 

Offline ltz2000

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Many years ago I got a badly damaged A10 amplifier and did some reverse engineering. Including the potted mu metal box, which was a real pain in the ass to open. I hope I can still find the documents. I don't promise that they are complete or correct, but it shouldn't be that difficult to fill in the gaps.

A10 circuit:

 

Online chuckb

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TR-286B ($393), core material 3E27.
Primary wire dia 0.004" over the insulation (difficult to measure), this may be 38 ga wire. The primary is center tapped. The DC resistance of each half of the primary is 1.55 ohms.
This would be 28.7 inches of 38 ga wire.


I noticed the primary center tap of the TR-286B transformer had a third wire attached to it. If you look closely at the center pin in the picture there are two red wires and one green. The extra wire is a larger ga wire. My guess is that it connects to an internal pri-sec electrostatic shield. Maybe that's why this transformer costs twice what the TR-285B costs!
 
 

Offline TiN

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Hm, what did he got here...

-

-

-

Few fails here and there, as usual for first rev...

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Online chuckb

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Looking Good!
 

Offline TiN

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Hmm, meter can't remember card, and I2C transfers seem to do nothing.

On power on I get two errors, 516 (Installed option id lost) and -241 (Hardware missing).



Perhaps it does not like 24C16 I put on? Original K1801 board using 24C01.
I don't have so small EEPROM, I thought they same for addressing? :)
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Offline ManateeMafia

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Is pin 7 pulled low (write protect pin)? I see on the 1801 schematics it is marked NC. Atmel states it should be pulled low for R/W.
 

Offline TiN

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Yea, it's low.
Pretty sure I got this gotcha. Old-ass Xicor X24C01 does not have device address (one like 0xA0 in today's 24Cxx ROMs), it just takes all data directly. And that's what Keithley feeding into bus as well, which I though as pooling device addresses is actually ROM address following DATA to write.  :phew: Good idea for sabotage young players - just solder this little ROM on PCB and it will corrupt whole multidevice-I2C, making sure you would not get any devices accessable  :-DD



Pesky little selfish bastard. Now I regret that did not put little 8bit AVR MCU on there.  :P
And ofc Digikey does not carry this ancient stuff, so good ol bay friend... Let's see.

chuckb

Which EEPROM chip you used?
« Last Edit: November 16, 2015, 06:04:05 pm by TiN »
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Offline TiN

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Good night photo for now..

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