TSP #19 - Teardown, Repair and Calibration of a Keithley 220 Programmable Current Source

In this episode Shahriar investigates the cause of failure of a Keithley 220 Programmable Current Source. Despite being manufactured in the mid-1980's, the Keithley 220 is still a very popular programmable current source. Alongside the repair efforts, the schematic of various analog, digital and power supply boards are also presented. By interpreting the failure mechanism, the fault is traced and corrected. The Keithley 220 is then calibrated and the calibration procedure of the sub-100nA range is explained. Finally, the performance of the calibrated unit is verified using a Rigol DM3068 Multimeter.
The Signal Path
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[@OctavMandru]

7 years ago when I started watching Dave tutorials I was a complete noob. The true impulse to actually start fixing expensive stuff came from you. I still am a noob, but a knowledgeable one. Thank you, Shahriar

[@Kevin-cr9jt]

im 55 new to electronics you have a wonderful gift you are a very intelligent young man .I wish I knew what you know when I was younger about this electronics age we live in.i enjoy your videos very professional and ive learned a lot.thanks

[@PaulHigginbothamSr]

Sweet. Thanks for the work and video. College teaching for us older folk. Sweet.

[@ChrisAnder4281]

Great Video. Your troubleshooting prospective has helped me analyze circuits much better. Thank you for the time and energy you put into these videos.

[@Henky-180]

Bijzonder leuk om de video's hier te bekijken. Erg leerzaam.

[@CrucialSpeaks]

GREAT VIDEOS! from a 45+ year component level technician with 48 certifications and vice president of CESDA (sub of NESDA) in 1980- 1983!! it was not a POT it was A rheostat the difference between a good technician and a bad on is, the good one can fix his own F' Ups! - Roger Smith, Southern sound and TV.

[@RBDInstruments]

Very easy to watch video. I work on a lot of analog electronics from the 70s and 80s so I was right at home with the components that Keithley used here. Great job of explaining the troubleshooting thought process.

[@donmoore7785]

Excellent job at explaining theory, design and practical limits/consequences.

[@SuperRnine]

Where the theory and practical meet. I really enjoy the repair videos you make. Please keep the good work.

[@ElectronicsIsFun]

Great video. I really enjoyed the debug session and the knowing that the op amp inputs should be at the same potential under normal operation. The fact that they we different show that the op amp was defective.

[@jimmy_jamesjams_a_lot4171]

THANK YOU for all your great hard work and demonstrating a bit of great troubleshooting on this nice piece of test equipment! I’m now leaning towards not selling mine, since I dont know what I might need it for next.

[@gnalibagatnortkelegn7561]

Very nice video about tear down and repair. As always, intelligently done. While for some it may appear that the fix is (in the end) easy, how one get there in a very systematic fashion requires both experience and very good understanding of the theory behind. Based on experience, an intermittent problem causing long hours of trouble shooting sometimes end up to "only" cleaning up bridging of dirt between sensitive paths of the circuit:-). Fix is easy but sometimes, it is a pain to get there. Thanks a lot. We are learning a lot of things from you. I hope you always have the time creating more interesting videos. I am now a fan of your channel!

[@cmdstraker]

Great video. Even though it takes a bit to load I appriciate the depth of your repair walkthough

[@jweismiller]

Great Video! BTW, a quick tip about 2-lug triax connectors - if you have a piece of equipment that you don't mind modifying, you can make them compatible with 3 lug connectors by filing off one of the lugs. I've done this on my old Keithley 602 electrometer and it works great.

[@gammypoofle]

Thanks for letting us join in on the process; very educational and at times exciting!

[@carldaniel6510]

Back in the 80's and 90's I worked on an instrument where we dealt with femtoamp currents. The ultra low current circuits were built on a Teflon PCB that had to be washed and handled very carefully to not throw off the measurements. I don't recall the Keithley current source, but we definitely had its counterpart - the Keithley picoammeter, which we used regularly in R&D. Good times.

[@DoRC]

I love these old keithley boxes. my 196 is the meter I use the most. so simple and you can see the display from across the block:)

[@Thesignalpath]

Thanks. I have some tutorials lined up and I will consider your suggestion as well.

[@ronaldlijs]

Excellent review/test/walkthorugh. This is the way to learn, keep up the great work Shahriar!

[@Thesignalpath]

Thanks for asking! It is the lighting in the room. I need some better lighting that does not cast shadows all over my face. It makes it look like I have not slept for a week.

[@Thesignalpath]

When calibrating using the 1GOhm and 100MOhm resistors, the multimeter is connected to the 'guard' voltage port and not across the resistors themselves. This is done for precisely the reason you are bringing up. Furthermore, the resistors stays completely isolated from the multimeter to keep injected noise at a minimum.

[@Nazral]

Looking sharp with that cap! Keep up the good work, yours is definitely one of my favorite channels on here.

[@bend0matic]

Love your videos sir. I repair test equipment full time and always take away something new from your vids!

[@federico8742]

nice video. when you cuts the long pins of the cap, the piece of the wire cutted, can jumps to anywhere. that's why you opens your hand to protect your eyes. instead of that, if with your finger only touches the pin it will be keep in place at the same time you're cutting. just remember the murphy laws. this piece of wire for example can jumps between the pins of one chip. or wasting time looking for it.

[@graemelaubach3106]

Best videos to relax to at the end of the day. You're killin it homie!

[@Darryl603]

Hi, If the button had been pushed in at the time of board removal, it would have allowed the proper clearance to allow the board to be lifted out without breaking the button. Thanks for posting and looking forward to the next. All the best...

[@Th3Su8]

Another great video, thanks for sharing. I appreciate your insights into troubleshooting and repairing devices. It was a long video, but I enjoyed it all the same.

[@Thesignalpath]

Many years of buying, fixing, etc. You thought this fix was easy? ;) Changing the OpAmp is easy, finding out that it was the OpAmp that was broken, not so easy!

[@putera131gaming7]

Yes correct not easy to fix electronic system.

[@parallelpath5749]

Great videos. Thank you a lot. If the diodes (and also the cap) were ok, which was the problem with the 24v instead of 30v?

[@irgski]

Nice step by step troubleshooting techniques! It would have been interesting to see if the failing op amp had any thermal issues - i.e. was it hot? Also, you should probably replace those 160V power supply caps as a suggestion.

[@First2ner]

love this long videos you do, repair, teardown,... hope to see many more

[@Bancroft12194]

It is a good thing you replaced that cap. I bought two keithley DMMs once (195 and 195A), and both had bad 10mF caps at the 5V regulator.

[@urbandiscipline88]

Thanks Shahriar!! you're my hero!!! Keep it up!!

[@free_electron]

Anytime i replace a filter cap due to defect or age i make sure to date the top of the capacitor with the year it was replaced - something you may want to do if you can still reach the capacitor once it is installed Mr SignalPath =]

[@michaelhawthorne8696]

I was wondering about the voltage of that 30V supply and why you called it HALF wave rectified when it looks more like FULL wave rectified with both halves of the sinewave on top. At the same time, the waveform looked rather clipped, is that your scope because there shouldn't be any way the circuit should do that as it stands.

[@kf7tkj]

I really enjoy these fixup videos!

[@sbreheny]

Great Video! It seems strange to me that this op-amp failed. I would think that a semiconductor component which is not significantly stressed, should take a VERY long time to fail. It must have been either made incorrectly, there was ESD in handling, an external surge (as you suggest, but is that op-amp really not protected from the output terminals?), or it was run under stress (high temperature or high current drain) but that would be a design issue.

[@Keith_Ward]

Nice work as always. Bummer about breaking the switch and unnecessarily changing out the cap but that how it goes sometimes. Overall easy repair of just an 8 pin op-amp though. As for the soldered section near the relays on the Teflon pads, would it still be hand-worked like that on a pcb like that today or are there new provisions that make it easier now?

[@CoolMusicToMyEars]

In the ideal world, On the lowest current range I feel this should be performed as a null against a reference voltage, a Null detector Fluke 845A & a reference supply perhaps 10 V reference from Fluke 745A feeding a Fluke Kelvin Voltage Divider "ideally", as voltage output under multimeter loading would have a drastic effect on accuracy on the lowest current range, also noting that both Fluke reference 845A & Fluke Null detector 845AB can be used on batteries, thus elimination of potential earth loops at low very low signal levels, when dealing with very low signal levels static charges can give false readings, that's why calibration laboratories have anti static flooring, & antistatic coat etc, I did enjoy watching your upload, thank you.

[@JoseSilveira-newhandleforYT]

Although 8 years later, I would point that the 741 was the only analog IC in a socket, suggesting that it may have been replaced before and hint that an error in operation was probably the cause.

[@andypandyc]

i love these tear down/repair videos thank you

[@putera131gaming7]

Very good troubleshooting video. Thank you for sharing. Regard Awang Azman Senior electronics tech.

[@davidelsea9938]

I think your videos are excellent. I like the way you explain what your doing and why your doing it. Sometimes you speak a little fast but I just back up and play again. Just wondering if you ever take on a viewer project, like a signal generator that the amplitude is not constant with increasing frequency. Keep putting out these great videos and I'll keep watching.

[@4833504F]

There's plenty of tutorials on pwm on youtube. I like how his videos are a little bit more in the signal theory niche

[@hugoschmeisser481]

Really nice Video. Unbelievable that the cap was fully operable, would have exchanged it also.

[@miceuz]

how much time do you spend cleaning dust from surfaces in your lab? :))

[@ivanv754]

How can you get so much test equipment!? Are all fixes this easy, overall? Great video, thanks for sharing.

[@youpattube1]

I was disappointed to hear you say that you were only going to do one more repair. Following your reasoning is very instructive.

[@jabramow]

Excellent video.

[@Thesignalpath]

Oh great! Thanks! ;)

[@houdini0118]

I really like your videos. They are well thought out and informative. But what are those clip wires called and were do you get them? They look really useful but i cant find a source of them.

[@JelckedeBoer]

Could you please explain the practical applications for this device?

[@JamesEncliffe]

At values like 1Gohm and above, I would expect humidity to significantly affect the value. Does this not happen, perhaps because the component has a hydrophobic coating?

[@czorgormez]

but what about the input impedance of your multimeter, did you consider about it ? i think you have to add your mesurement resistor+multimeter input impedance when you calculate the output voltage.

[@davidgrey943]

Another very interesting video and repair I envy your set up wish i had the same question have you done that series on phase locked loops. Can you do a series on pulse conditioning interfaces using discrete transistors. Many thanks for your time and effort David Grey.

[@kieranj67]

Excellent, thank you

[@Thesignalpath]

Yes, I should have removed it first. But alas, a brand new shiny blue cap wouldn't hurt! ;)

[@t1d100]

Excellent

[@sazhen86]

Great video, thanks! Lucky that IC was in a socket.

[@ubuntututorials]

That cap is -probably- OK. Many capacitors with those plastic vent discs tend to show bulging -- but if you pull off the disc (used for insulation) you'll find the vent underneath is unbroken.

[@efox29]

Where do you buy all these "broken" stuff ? Is broken equipment relatively expensive as well ?

[@frankvde8964]

Apparently they knew they had to put the 741 on a socket :)

[@ohmedarick1]

I agree

[@ROBERTHOCKER]

Keithley, and Tektronix are the absolute BEST electronics...

[@maybles1]

So when yoy testing the opamp what did u refrence at ground since there are multiple references

[@Keep-Exploring128]

Great video... thanks

[@DerTabak]

Wow Teraohms, never heard that term in a practical application :D

[@erin19030]

What do you do with one nano amp?

[@DLTX1007]

It's possible the cap gassed a little without having the notch bump at all (Oh, it seems your new cap is quite old too :P my new chemicon 10000uF 50V cap is smaller in both X,Y axis)

[@reachingout9285]

I am confused how the output and input work on this machine

[@zullottrocker]

At the and of the vid did you just switched the multimeters cabels from current measurement to voltage measurement without switching the multimeter into volt measurement mode? It must be a really good equipment, if I did this to my cheap stuf I would have created a nice smoke cloud.

[@Thesignalpath]

Yes, the damn thing was perfect! I still have no idea where the bulge could have come from.

[@franciscoassisgomes1]

como se calcula a velocidade da bobina para produzir 50v

[@destenylol]

Nice , dude you always find where the problem is! good work! can you please make some videos about how to programm a microcontroller so it can regulate the dc motor speed using pulse widh modulation? Would be very helpfull. But if you cant , feel free to send me some e-books , documents about it :) Thanks

[@MrMac5150]

Good One, more repair videos, help me find some low cost equipment.

[@efrain2423]

Could You tell me Where you get the schematics?

[@EvanZalys]

If it makes ya feel better, I broke one of those exact same schadow switches while taking apart an old tek scope, except it was potted inside a power entry module 😂😂😂

[@NerdNordic]

Sweet! :D

[@Nermash]

Only true enginneers drink Becks:) Great video Shahriar!

[@gacherumburu9958]

👍👍

[@PlasmaHH]

I spot a becks there! good boy! ;)

[@Raldenaldrin]

Is this an ac voltage source?

[@AureliusR]

uh... no. It's a DC current source, as he said multiple times.

[@SolidStateWorkshop]

I don't think that cap is bad. It's just the natural bulge in the plastic cap.

[@Arek_R.]

Capacitors didnt dried. But the opamp dried... xD

[@bkupiec]

I'll trade you my ESR meter for your DSA1030A and you'll never have to worry about replacing a good cap again. ;)

[@Orcinus24x5]

Don't you just hate when that happens? I get so frustrated when I replace parts that aren't actually defective. It wastes time and money. :/

[@samsaga]

You sound a little bit drunk. That Beck's got you.

[@destenylol]

yes, i have seen lots of them , but i still need to undesrand it better, im not that good, i think electronics are cool!

[@gamccoy]

Please, do not wear your watch around open, energized equipment. We want to keep you healthy and making more videos.

[@ryebis]

It might be better to use "DAC" 🤣

[@federico8742]

nice video. when you cuts the long pins of the cap, the piece of the wire cutted, can jumps to anywhere. that's why you opens your hand to protect your eyes. instead of that, if with your finger only touches the pin it will be keep in place at the same time you're cutting. just remember the murphy laws. this piece of wire for example can jumps between the pins of one chip. or wasting time looking for it.