Keithley 614 Electrometer - Repair [Success] - Page 1
Forum section: electronics / repair

author: HighVoltage
author_rank: Super Contributor
timestamp: June 04, 2016, 10:45:20 am
content: This was a great deal, as long as I get it repaired and restored, my first Keithley Electrometer.Keithley 614 ElectrometerMade in the USARev. FProblem:- Does only turn on intermittently- Shows random numbers on the display- Has a part of the front bezel broken outThis meter is also battery powered, but the batteries are deadI will first have a look at all the switches, which feel a little sticky.The front panel has a old style Triax Input connector with two pins like a typical BNC connector and not the new 3 pic triax connector.Hmm, I wonder if I should exchange the input connector to a more modern type.But first, lets get it back to work.Anyone here have experience with this 614 Electrometer?

author: HighVoltage
author_rank: Super Contributor
timestamp: June 04, 2016, 12:16:25 pm
content: OK, I was so much bothered by the damage on the front bezel plastic part, I fixed it firstStep 1: Clamp two aluminum pieces with double sided tape against the bezel.Step 2: Fill the slot very slowly with some epoxy resin.Step 3: Use fine sandpaper to grind it to perfectly matching shapeThe color is not completely matching but the shape is perfect.May be I will have a calibration sticker right there and then nobody will notice.I am happy with the plastic repair but just not with the color.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 04, 2016, 12:24:06 pm
content: Here are some specifications of this 4.5 digit Keithley 614 Electrometer- Detecting currents as low as 10^-14 A- Resistances up to 2 x 10^11 ohms.- It provides more than 5x10^13 ohms input impedance on the voltage ranges- Can detect charge over a range of 10^-14 to 2 x 10^-08C.- Voltage ranges are 0.2 V to 20 V in 3 ranges with accuracies to 0.08%.- Current ranges from 20 pA to 2000 µA in 9 ranges with accuracies from 1.5 to 0.3%.- Resistance ranges are from 2 kohms to 200 G-ohms in 9 ranges with accuracies from 0.5 to 2%.

author: TiN
author_rank: Super Contributor
timestamp: June 04, 2016, 04:10:45 pm
content: Beauty. HighVoltage is running ahead, getting first electrometer. I should do something about that asap.Interesting trick with panel repair. Perhaps paint it with matching color later to have it look genuine?For example, repair 41422A SMU module...

author: vindoline
author_rank: Unknown
timestamp: June 04, 2016, 06:44:25 pm
content: HighVoltage, nice job on the plastic repair! What kind of epoxy did you end up using??Also, you look lucky with the triaxial Jack. It looks easy to replace if you want. I have a Keithly 616 and it looks to be a bear to get to the Jack to change it. The mod I did (and it's a bit of a hack) is to file off one of the lugs on my input jack. I can now use either 2 or 3 lug cables.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 04, 2016, 07:45:11 pm
content: The 614 manual include schematics, which should make a repair relatively easy. The ADC is a standard ICL7135 - so easy to change if needed. IF the input FETs are broken it might get difficult to find some as good as the original, but at least reasonable performance should be easy to get.Intermittent turn on points toward the power supply part. Could be trouble with caps or the oscillator. This would be the first part to check anyway.

author: Smith
author_rank: Frequent Contributor
timestamp: June 05, 2016, 07:46:11 am
content: I know there is a trick for the 617 input. There are some good and cheap opamps (LMC662) wich offer a beter and more (temp) stable input. Just take a look athttps://www.eevblog.com/forum/testgear/fun-with-low-leakagebias-current-femtompere-electrometer-keithley-617/Btw before replacing the triax with a three lug triax you might want to check for some cables with two lug triax. I know the 3 lug are very expensive, the 2 lug might be a bit less expensive.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 05, 2016, 11:17:07 am
content: Some interesting suggestions, ThanksI might paint the bezel later.Here are some more pictures.Display PCBAnd the 50 T ohm input arrangement on Teflon standoffs

author: HighVoltage
author_rank: Super Contributor
timestamp: June 05, 2016, 11:41:00 am
content: Quote from: vindoline on June 04, 2016, 06:44:25 pmThis is the resin type epoxy I used.I added some black and little yellow color, to get a matching brown, but that failed.It is pretty strong attached to the original plastic.

author: Johnny10
author_rank: Frequent Contributor
timestamp: June 05, 2016, 03:24:08 pm
content: Didn't FeedbackLoop just go over one of these on You tube?I think problems with switches.Will have to look at that again.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 05, 2016, 04:43:14 pm
content: Today I cleaned all switches but it did not helpNext is the power supply testing+/- 5V is okBut it seems the 32V rail is sitting at 25 Volts hmm

author: feedback.loop
author_rank: Frequent Contributor
timestamp: June 05, 2016, 04:52:29 pm
content: Quote from: Johnny10 on June 05, 2016, 03:24:08 pmThat is right. The switches were the culprit in my case. I also fitted a 3-lug triax connector.Here is the video:https://youtu.be/txH6EpqN5V0

author: HighVoltage
author_rank: Super Contributor
timestamp: June 06, 2016, 07:19:57 am
content: Thanks Feedback.Loop for the link to your great video.After cleaning all the switches on my 614 it turns on perfectly but still shows strange and random numbersTime to get out the schematics and start at the power supply

author: HighVoltage
author_rank: Super Contributor
timestamp: June 06, 2016, 08:16:45 am
content: By total surprise, I found an old original Keithley 2-lug connector and cable in a local store here in town.I will just install some banana plugs on to the cable and see how good it performsIt will be a good start and I don't have to exchange the connector in the instrument.

author: HighVoltage
author_rank: Super Contributor
timestamp: June 11, 2016, 01:46:00 pm
content: The repair was a success !The power supply had a bad regulator, not sure why, no obvious reasons are visible and it works perfectly now.Calibration was easy as well.But my lowest current source is the Keithley 2450 SMU and it does "only" do 1nAAnd the Keithley 614 has a pA rangeHmm, no way to test it.I think I will hold off on the painting. The repair of the bezel does look ok as it is.Now I need to build a metal enclosure for high resistance measurements.I am amazed by this little and old Keithley 614 and its capabilities with 50 Tera Ohm input resistance.Verification:1 nA1 uA19.0 V

author: Smith
author_rank: Frequent Contributor
timestamp: June 11, 2016, 10:51:29 pm
content: One method i found out to be helpfull, in need of some Tohm resistors: use a standard LED as a current source, and take down the light until your range reaches about 10% full scale, then range down one scale. Not absolutely accurate, but good enough for testing. BTW, it does differ a lot depending on your light and the type and color LED. You could even use a second LED to shine on the first one to make it a bit more stable and controlable, but rember the setup is quite temperature dependant (due to the leds themself).