Author Topic: Keithley 2400 SourceMeter review and teardown  (Read 29384 times)

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Offline plesa

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #50 on: November 23, 2016, 06:16:07 pm »
I will take picture with infrared camera,  this was helpful during my repair.
If you cannot find bad transistor, desolder transistors and test them within operating conditions.
Firmware recommended is C32, C33 has delay to work properly at 90V in mains :) I needs to downgrade, the startup delay was annoying.

BTW is anyone interested in purchasing new VFD DD-51 for Keithley gear, send me PM.
 

Offline z01z

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #51 on: November 25, 2016, 02:59:30 pm »
Yes, that startup delay is very annoying, I also went back to C32 because of that. It should be made selectable somehow.
 

Offline plesa

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #52 on: December 01, 2016, 09:28:02 pm »
Christmass for Keithley gear  :-/O
 

Offline plesa

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #53 on: December 18, 2016, 08:50:12 pm »
Time to replace few VFD on various Keithley gear. New VFD are little bit smaller with contacts in one line.
VFD holds on PCB 3M VHB double side tape ( reel 33m/150 EUR).
Contacts are soft and easy to bend. By tweezers I select pins row and later align all in two rows by PCB.
After that started from one side and with tweezers I put each pin into hole by tweezers.
After two hours is repair of K2400 finished ( forgot to connect analog board  - Over temperature )
 

Offline ivonenand

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #54 on: January 02, 2017, 11:38:26 am »
Hi guys,
Does anyone know, how the output current sense is implemented in this SMU (or any other for that matter)? The thing is, you need extremely high CMRR, since the output is anywhere in the +-200V range. Second, the SMU offers better than 1uA resolution, so there must be little or no leakage on the amplifier connected to the output shunt. You cannot do that with a standard differential amplifier.

Any ideas on how the amplifier connected to the output shunt is implemented?

Regards,
Ivo
 

Offline VintageNut

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #55 on: January 02, 2017, 10:36:00 pm »
Hi guys,
Does anyone know, how the output current sense is implemented in this SMU (or any other for that matter)? The thing is, you need extremely high CMRR, since the output is anywhere in the +-200V range. Second, the SMU offers better than 1uA resolution, so there must be little or no leakage on the amplifier connected to the output shunt. You cannot do that with a standard differential amplifier.

Any ideas on how the amplifier connected to the output shunt is implemented?

Regards,
Ivo

I do not have a schematic for the 2400. My assumption is that the 2400 is not far from the 238 as far as architecture. The 238 schematic exists as a printed document.
working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline plesa

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #56 on: January 02, 2017, 10:53:53 pm »
Hi guys,
Does anyone know, how the output current sense is implemented in this SMU (or any other for that matter)? The thing is, you need extremely high CMRR, since the output is anywhere in the +-200V range. Second, the SMU offers better than 1uA resolution, so there must be little or no leakage on the amplifier connected to the output shunt. You cannot do that with a standard differential amplifier.

Any ideas on how the amplifier connected to the output shunt is implemented?

Regards,
Ivo

Check this thread, where is link for schematic of one of Keithley SMU.
https://www.eevblog.com/forum/testgear/keitley-236-teardown-and-review/
2400 is quite similar ( at least output stage, which use the same transistors.
 

Offline plesa

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #57 on: March 12, 2017, 04:30:08 pm »
Unbelievable repair  :)

 

Offline julian1

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #58 on: March 12, 2017, 09:39:38 pm »
I did a repair on a 2420 which had burnt power mosfets driving a secondary DC-DC SMPS. The interesting difference with the 2400, is that the power-board and digital board are combined. In contrast, the 2400 uses a third-party non-Keithley power board.

The same pcb is used for the 2430 as well (the silkscreen has a tickbox)- and possibly other high-current output models. Here's a pic of the board,


Offline z01z

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #59 on: March 13, 2017, 09:29:33 am »
Unbelievable repair  :)

It is :)
Then bumped into a video on youtube from , about a secret menu in K2400.
 

Offline TheSteve

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #60 on: August 05, 2017, 05:52:12 am »
Used TiN's script to calibrate a 2400 from a 3458A - worked fine but I did make one change so it didn't turn my screen background to yellow during the DCV calibration.
Changed sys.stdout.write ("\033[0;43m*") to sys.stdout.write ("\033[0;40m*") to maintain a black background.


Thank you TiN for the script!
VE7FM
 

Offline TiN

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #61 on: August 05, 2017, 07:26:48 am »
Proper would be \033[0;49m ANSI escape sequence, this means default background color.
YouTube | Chat room | Live-cam | Have documentation to share? Upload here! No size limit, firmware dumps, photos.
 

Offline eeviking

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #62 on: November 14, 2017, 05:17:57 pm »
Hi
I just scored a Keithley 2400 with a vague "powers off randomly" fault description. It was pulled from a test rack, so was probably running hot for years.
From the description I would suspect bad caps in the psu. Haven't seen the problem yet, but only did some quick tests.
Top board looks clean, haven't torn it down to look at the bottom psu boards yet. It's from around 2001 so a year younger than TiN's.
Question is: Should I just replace all caps?
Anything to look out for? What will be lost if the battery is removed?
 

Offline Jens01

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #63 on: May 15, 2019, 05:53:41 pm »
As an addition to the information already shared here on the forum, here my $0.20.

Bought an defect 2400, bought as broken/for parts. Unit came from a automated test set-up so visually in good condition. Symptoms:
- -240V on banana jacks when output was disabled
- When enabled, the current reading was always off by 9.8mA. When sourcing 9.8mA, the current measured with the output shorted with a DMM in current range was zero. The leaking current was independent of the selected current range.
- The voltage reading was always wrong. Also, when sourcing 50V, the output went up to +240V.

There are quitte some usable test pads on the board. My 2400 differs quite a bit from the photo's from TiN, but here are some hints based on the testpoint labels on TiNs 2400:
- TP201 'NVDAC' and TP203 'NIDAC' referenced against FCOM: respectively DAC voltage and current setpoint. Range dependent, but should linear change when giving a new setpoint.
- TP214 ' EAMP' referenced against FCOM: difference of voltage between pin 2 and 3 of U500. Zero volt means that the setpoint voltage matches the feedback voltage, indicating that the amplifier stage is probably working OK. When reading other than zero volt: output stage clips or is defect.
- TP221 '+si' referenced to TP222 '-si': feedback current. Range dependent, should linear rise with measured output current.
- TP227 '+sv' referenced to TP228 '-sv' feedback voltage. Rang dependent, should linear rise with measured output voltage.

I started with reverse-engineering the output stage, as they seem to fail very often and reverse engineering is easily done as the components are mostly on the top side. The list of designators in K2400 service manual did not match the numbers on the PCB, but it did match with the designator list in the K2410 service manual. Obviously the high-voltage part will differ, but the < 30V part seemed to match well.

Eventually i found out that my unit had a fully working output stage. if i knew about that EAMP testpad before i started.. :palm:
The setpoint dacs seemed to work so the feedback path was the next step to debug. The current feedback path is located near the blue resistor on the front side of the PCB and the voltage feedback path is located next to the black relay on the right side.

 


This component, Q233 on TiNs photo, became very hot when driving the output to a high voltage. As the voltage reading was always wrong, i eventually found out that op-amp U219 (OPA124) had a large voltage difference between the inverting and non-inverting input. As this op-amp is a simple high-impedance voltage follower, i tested it out of circuit to make sure the output was not externally clamped. With success, the output was stuck at -15V :)

Replaced the opamp and now she's fine again.

« Last Edit: May 15, 2019, 05:55:17 pm by Jens01 »
 

Offline Kjelt

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #64 on: May 15, 2019, 09:05:01 pm »
Bought an defect 2400, bought as broken/for parts. Unit came from a automated test set-up so visually in good condition.
Troostwijk solar factory auction ? Missed those, the prices skyrocketed  :(
 

Offline Jens01

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Re: Keithley 2400 SourceMeter review and teardown
« Reply #65 on: May 16, 2019, 05:40:36 pm »
Bought an defect 2400, bought as broken/for parts. Unit came from a automated test set-up so visually in good condition.
Troostwijk solar factory auction ? Missed those, the prices skyrocketed  :(

No, Ebay. The name 'Keithley' was misspelled, so i was just lucky to be at the right time at the right place. ;)
 


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