Author Topic: Electrometer output stage , keithley 6517  (Read 24976 times)

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Offline harrimansatTopic starter

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Electrometer output stage , keithley 6517
« on: March 13, 2015, 10:41:38 am »

 

Please is there anybody familiar with current electrometer output stage? Some schematic and photos will be really appreciated.
Any body knows how works outupus stage? 4 HV mosfets, 2SK1412, lm334 current source as a mosfets drivers.
Positive output works well, but negative output only reach about -700V


Thanks
Regards




« Last Edit: March 13, 2015, 12:06:41 pm by harrimansat »
 

Offline codeboy2k

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Re: Electrometer output stage , keithley 6517
« Reply #1 on: March 13, 2015, 03:15:10 pm »
Here's the service manual.  It has no schematic.

http://exodus.poly.edu/~kurt/manuals/manuals/Keithley/KEI%206517A%20Service.pdf

Go through section 5, there's tables of voltages to be checked.  Check them first.

Keithley might mail out a schematic if you ask them.


 

Offline macboy

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Re: Electrometer output stage , keithley 6517
« Reply #2 on: March 13, 2015, 03:37:37 pm »
Here's the service manual.  It has no schematic.
...
Keithley might mail out a schematic if you ask them.
:-DD
 

Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #3 on: March 13, 2015, 04:46:17 pm »
We want mooore photos , please!
Did you check -1100V rail?
Does it fail any selftest?

Also please try secret menu like this one, does 6517 have it?
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Offline codeboy2k

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Re: Electrometer output stage , keithley 6517
« Reply #4 on: March 13, 2015, 08:07:21 pm »
codeboy flings poutine @macboy...
 

Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #5 on: March 14, 2015, 10:47:04 am »
Might be farfetched, but have you tried calibrating the output? You can calibrate the output voltage via the calibration menu with just a decent multimeter.
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Offline harrimansatTopic starter

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Re: Electrometer output stage , keithley 6517
« Reply #6 on: March 14, 2015, 10:55:27 am »
codeboy flings poutine @macboy...

Yes, all supply voltages are ok, no error message. All works well, but not reach -1000V, only arrives to -721 volts. I will try to make a little schematic, is like a op with opto feedback. TLP590B.
Thanks to all for answers, more photos




























 

Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #7 on: March 14, 2015, 11:12:23 am »
Ha, ADC module is from Keithley 2001. Nice.

You may want to draw simplified signal diagram for high voltage path, to find suspected parts which can cause your issue. Its likely something on output stage.

So you check CR304,CR305,C311-313,C315-C317 and they have -1200V/+1200V on VR303,VR304?
Check if VR311 anode have -1200V too, when set voltage source to 100V and operate is ON. U308 pin 4 should have 4.81V. Measurements against V Source Lo.
« Last Edit: March 14, 2015, 02:13:11 pm by TiN »
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #8 on: March 14, 2015, 04:51:27 pm »
Is this thing any different from a 6517A? In the 6517A SM they mention DAC U308 and ranging circuit U209 controlling the output stage. Might be the same as yours.
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Offline harrimansatTopic starter

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Re: Electrometer output stage , keithley 6517
« Reply #9 on: March 14, 2015, 05:21:58 pm »
Is this thing any different from a 6517A? In the 6517A SM they mention DAC U308 and ranging circuit U209 controlling the output stage. Might be the same as yours.

It seems that is an error in the block diagram, ranging circuit is U307, AD548KN
 

Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #10 on: March 15, 2015, 07:45:08 am »
I am surprised it uses a 2001 ADC module. 2001 is 7,5digit, 6517x is 5,5 digit if i remember. Although as i remember correctly the settings menu has a 6,5 digit setting.

This ADC might be a good thing, as I am trying to repair a 6517A with lots of issues on the input circuits, and there isn't much info to be found on the 6517x themselfs.
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Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #11 on: March 15, 2015, 08:09:02 am »
Well, if there is no much info, then its time to start posting, and I am sure we will end up having other people with 6517's join as well. I would love to see some nice photos of more gear from Kei, since its usually not easy to find, likely due to pricing outside of most hobbyists even for very old gear.
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #12 on: March 15, 2015, 09:36:13 am »
We might be lucky as the Keithley 6517 and 6517A are only being repaired on a best effort repair, as some spare parts cannot be obtained no more. So people might as well put them on Ebay  :-+
One thing to mention is the display. You cannot obtain the FVD from Keithley like most other Keithleys. You  can only obtain the whole display module, wich sets you  back about 420 euro/500dollar ex vat if I remember correctly.
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Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #13 on: March 15, 2015, 09:49:09 am »
6517 are for sale from time to time on ebay, but usually rather expensive for repair-at-weekend project.
As of displays, there is always alternative way, to buy Keithley 7001 and salvage VFD from it. That's exactly how I repaired my 2400.
Sometimes 7001's go as low as 50$USD on bay... And you will get extra goodies, like nice chassis for DIY projects, SMPS, processor and VFD DC-AC module (same as used in 2001/2002).
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #14 on: March 15, 2015, 01:16:17 pm »
As far as i know there are 3 types: 6517, 6517A and 6518B. There was an official upgrade from Keithley to make a 6517A out of a 6517.  This 6517 looks a lot like the 6517A I had a look at. Unfortunately I couldn't take our 6517B apart :-//
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Offline free_electron

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Re: Electrometer output stage , keithley 6517
« Reply #15 on: March 15, 2015, 03:22:28 pm »
That driver stage with the four transistors looks identical to the older electrometers.

Find a service manual for an older electrometer and look how they do it there.
The principle will be the same. Keithley rewashed that circuit over and over.

Most likely you will find one of the fets is permanently 'on'. You can only get to -719 because one of thets in the positive section cannot come out of conduction.

This thing is a push pull amplifier you go full negative by turning the drivers to negative full on , and the drivers to positive full off.  (It is a two quadrant output and can both sink and source current at the same time. No matter if you sink or source current the system keeps the ouput voltage fixed

So if you cant go full negative, and the -1000 volt rail is ok, it means something is injecting too much 'positive' in the output node.

So that is where you need to start looking. My 2 cents says the fault is in the transistor ladder from +1000 volt to output.
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Offline harrimansatTopic starter

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Re: Electrometer output stage , keithley 6517
« Reply #16 on: March 15, 2015, 10:33:55 pm »
Fake mosfets from ebay, from UTSOURCE, seller UTSOURCE STORE, hkutsource, max.V DSS 900, this electrometer needs 1500V mosfets.
Now is working with good mosfets.

Those ones are fake transistors:

http://www.ebay.com/itm/5PCS-2SK1412-Encapsulation-TO-220-High-Voltage-High-Speed-Switching-/131213219499?pt=LH_DefaultDomain_0&hash=item1e8cead6ab


FAKE cheap transistors from ebay are not always good!!!  |O because normally I don't have problems with ebay semiconductors I don't check it before to install.  |O Two days working for nothing, but now is working.

I attach some photos with measurements made with my curve tracer. Thanks to all!!!

ORIGINAL 1500V

FAKE 900V

ORIGINAL HIGH RDS

FAKE LOW RDS

WORKING AGAIN!

ORIGINAL LEFT / FAKE RIGHT







That driver stage with the four transistors looks identical to the older electrometers.

Find a service manual for an older electrometer and look how they do it there.
The principle will be the same. Keithley rewashed that circuit over and over.

Most likely you will find one of the fets is permanently 'on'. You can only get to -719 because one of thets in the positive section cannot come out of conduction.

This thing is a push pull amplifier you go full negative by turning the drivers to negative full on , and the drivers to positive full off.  (It is a two quadrant output and can both sink and source current at the same time. No matter if you sink or source current the system keeps the ouput voltage fixed

So if you cant go full negative, and the -1000 volt rail is ok, it means something is injecting too much 'positive' in the output node.

So that is where you need to start looking. My 2 cents says the fault is in the transistor ladder from +1000 volt to output.
« Last Edit: March 15, 2015, 10:37:43 pm by harrimansat »
 

Offline harrimansatTopic starter

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Re: Electrometer output stage , keithley 6517
« Reply #17 on: March 15, 2015, 11:27:27 pm »

That driver stage with the four transistors looks identical to the older electrometers.

Find a service manual for an older electrometer and look how they do it there.
The principle will be the same. Keithley rewashed that circuit over and over.

Most likely you will find one of the fets is permanently 'on'. You can only get to -719 because one of thets in the positive section cannot come out of conduction.

This thing is a push pull amplifier you go full negative by turning the drivers to negative full on , and the drivers to positive full off.  (It is a two quadrant output and can both sink and source current at the same time. No matter if you sink or source current the system keeps the ouput voltage fixed

So if you cant go full negative, and the -1000 volt rail is ok, it means something is injecting too much 'positive' in the output node.

So that is where you need to start looking. My 2 cents says the fault is in the transistor ladder from +1000 volt to output.

Thanks, but this is not a usual push pull amplifier, 4 power HV mosfets N driven with lm234 z6, one opto and one 2N7000. It works in two ranges, with 3 electronic relays, 120v and 1200V.

[/quote]
 

Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #18 on: April 19, 2015, 11:59:33 am »
Was looking thru C05 firmware for 6517, and did found secret menu strings in it.
May you help to check if secret menu opens up in MENU/GENERAL if press combinations like OPER+TRIG during power on?
I would like to update secret menus article, if possible :)
Thanks!
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #19 on: April 19, 2015, 04:43:55 pm »
I will be looking around for some 4mbit EPROMs to flash the 6517A C05 firmware.  Maybe I'll flash the original EPROMs, but I'm not quite sure how the UV lamp performs (I've never used it before, just like the programmer ^-^).
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Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #20 on: April 19, 2015, 04:57:14 pm »
It takes about 20min to erase chip with DIY UV barbarian setup..
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #21 on: April 20, 2015, 10:56:58 am »
I used the original EPROM's to flash the C05 firmware, but it didn't work. It just hangs at Checking ROM. Maybe I did something wrong converting the .x to bin files. Guess I have to go back to the C03.
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Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #22 on: April 20, 2015, 11:30:46 am »
I think ending got you :)  ;D
Did you try big-endinan binary?
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Offline Smith

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Re: Electrometer output stage , keithley 6517
« Reply #23 on: April 20, 2015, 11:49:01 am »
No I didn't. It was ages ago when I last programmed an EPROM. Could you convert the .x to the ODD and EVEN binary for me?

UPDATE: The only difference between the normal and big endian type would be eliminated when both files are dissected aren't they?
« Last Edit: April 20, 2015, 01:54:30 pm by Smith »
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Offline TiN

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Re: Electrometer output stage , keithley 6517
« Reply #24 on: April 20, 2015, 03:12:55 pm »
Yes, endianess would be matter which file would be called even, which one odd.

Bodged a quick tool to do splits, opposite to merger one I did long ago for 2001's.

Here's result:

6517 Firmware C05, EVEN Binary
6517 Firmware C05, ODD Binary

I just realized, that I can give it a try on my 2001 board :D
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