EEVblog #478 - Keithley 2015 THD Multimeter Teardown

[Oracle]

really like this multimeter... Added to my future purchases list...

[lewis]

Nope. Bought it (2700 series http://www.ap.com/products/2700) from my previous company that was shutting down for $500! Hardly used, and just freshly cal'd.

Lucky effing Bastard!!!!!!!! AAARGH! Would have given my back teeth, both arms and all four legs for that!

[flodins]

Excellent, but what is this weirdo for? Some pick up antenna? Really strange. http://wstaw.org/m/2013/06/05/8955197658_87404b74c4_o.jpg

[bitwelder]

Dave, talking about Keithley, when do you plan to show/teardown the MegaohmPetaohm bridge (Keithley 515A) you got at a recent auction?
I'm really curious also to see some application for it.

[Dave]

"...you might be able to get one fairly cheap..."
Nope, not anymore.

I have seen a wobbly LM399 creamic case before. I'm quite sure they are mounting it like that on purpose. Does anyone know the reason why?

[Sine]

Hey guys, my first post here.

Carefull with those electrolythics next to the 15V regulators, I have bought three 2000's and on two of them these caps had gone leaky, destroying parts of the powersupply and analog circuitry.

One of them is beyond repair, an other I managed to fix. The accuracy of these meters is just ridiculous.


Inside shots :
http://www.gigawatts.nl/co/projects/Keithley_2000/overall_keith.JPG
http://www.gigawatts.nl/co/projects/Keithley_2000/leaky_keith.JPG

[free_electron]

Dag Sine :p

Yep. i've seen multiple 2000's with bad electrolytics. typically the MELF diodes ( ML4007)
die as well.

[plesa]

"...you might be able to get one fairly cheap..."
Nope, not anymore.

I have seen a wobbly LM399 creamic case before. I'm quite sure they are mounting it like that on purpose. Does anyone know the reason why?

It is not ceramic it it made from plastic. Keithley are using the same refference on K2015,K2000, and following K6485 and K6487.
I suppose that main reason for this capsule is the termal stability. In Keithley 2002 and Keithley 2002 where is used the LTZ1000A  is keithley custom made cap.
http://www.xdevs.com/attachments/download/208/2_3_ace27d41477113b.jpg

This can be useful to someone who score on 2015 or 2000 on ebay:
http://bardagjy.com/?p=1167

If anyone have access to schematic for 2002/2001 please let me know.  One 2002 still waiting under my bench for repair
The DC reading is OK and accurate, issue is in the ohm measurement and amps.

[Dave]

It is not ceramic it it made from plastic. Keithley are using the same refference on K2015,K2000, and following K6485 and K6487.
I suppose that main reason for this capsule is the termal stability. In Keithley 2002 and Keithley 2002 where is used the LTZ1000A  is keithley custom made cap.
http://www.xdevs.com/attachments/download/208/2_3_ace27d41477113b.jpg

You are right about that. I have checked the datasheet for the material of the outer capsule. It's made from a resin called Valox 420 (low thermal conductivity and extremely low electrical conductivity).
I understand why the references are inside a case, but what I'm trying to figure out is why are they mounting it with a large offset from the board? Why don't they just mount it flush with the board, so the case doesn't wobble around? Just by clarifying my original question, I answered myself. The leads of the reference certainly have a different thermal expansion coefficient than the resin case. If they mounted it flush with the board, the changes in temperature would cause mechanical stress on the reference, which kills the precision. Feel free to correct me, if I figured it wrong.

[fmaimon]

How worried should one be with this electromigration problem? I will probably buy another 6 1/2 meter in the next semester and it's hard to buy anything in here, including spares to fix any problems that may arrive.

https://www.eevblog.com/forum/projects/keithley-2000-gain-repair/
https://www.eevblog.com/forum/projects/keithley-2000-gain-repair/msg229818/#msg229818

[Galaxyrise]

How worried should one be with this electromigration problem? I will probably buy another 6 1/2 meter in the next semester and it's hard to buy anything in here, including spares to fix any problems that may arrive.

To fix mine, I ordered a Caddock 1k-9M resistor network.  I haven't done the repair yet, so I haven't updated that thread, but for the resistors that happened to die for me, that was a convenient fix.

But even better, it looks like the 2015 uses different resistors there!  Compare that part of the board from Dave's teardown. Edit: Of course, it could also be that newer rev 2000's work that way too; mine is from 99!

[TMM]

Looks like a nice unit but i'm not sure it's worth paying extra for a THD capability when you only get a -65dB floor. For the applications they list, the FFT capability on most cheapo scopes would probably do the job. I guess the attraction is ease of use and having the function gen built in. It would be interesting to see whether the performance is limited by the function gen or the ADC.

If you don't mind a PC solution, some cheap USB interfaces like the E-MU 0204 are capable of very impressive numbers (<-105dB THD, <-125dB noise floor) with some light modifications, which is about as good as you'll ever need for audio applications.




 

[don.r]

If you don't mind a PC solution, some cheap USB interfaces like the E-MU 0204 are capable of very impressive numbers (<-105dB THD, <-125dB noise floor) with some light modifications, which is about as good as you'll ever need for audio applications.

I'm interested in this approach. Could you provide a link for these mods? Is it something done on head-fi.org by any chance?

[TMM]

If you don't mind a PC solution, some cheap USB interfaces like the E-MU 0204 are capable of very impressive numbers (<-105dB THD, <-125dB noise floor) with some light modifications, which is about as good as you'll ever need for audio applications.

I'm interested in this approach. Could you provide a link for these mods? Is it something done on head-fi.org by any chance?

http://www.diyaudio.com/forums/equipment-tools/231426-emu0204-mods-fft-measurements.html

[don.r]

If you don't mind a PC solution, some cheap USB interfaces like the E-MU 0204 are capable of very impressive numbers (<-105dB THD, <-125dB noise floor) with some light modifications, which is about as good as you'll ever need for audio applications.

I'm interested in this approach. Could you provide a link for these mods? Is it something done on head-fi.org by any chance?

http://www.diyaudio.com/forums/equipment-tools/231426-emu0204-mods-fft-measurements.html

Excellent! Bookmarked.

[Watermelon]

What about W303? High voltage jumper link? Current shunt? Temperature measurement? Anyone?

[free_electron]

W303 : loop to connect ground crocodile clip of scope probe

TP310 standard SMD testpoints as made by keystone and others.

[don.r]

W303 : loop to connect ground crocodile clip of scope probe

TP310 standard SMD testpoints as made by keystone and others.

Always the sign of a quality instrument. You can see test point posts all the time in older HP equipment.