EEVblog #777 - Keithley 177 Microvolt DMM Repair

Come on a ride as Dave repairs an intermittent Keithley 177 Microvolt DMM, garden paths and all.
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[ConstantlyDamaged]

As a programmer, I am glad I am not the only one who spends hours looking for bugs only to find a bad input management.

[DougEStile-gjwy]

Before I retired I worked as a bench technician for a small electronics manufacturer, and we used several Keithleys similar to this one, mainly because the boss was too cheap to get us newer DMM's. They worked well, and I liked that the displays were so easy to read. Seeing this one and hearing the switches click brought back some memories. Cheers!

[greengrayradio]

Nice as always, Dave! I spray those switches from the rear, they are open there, and the cleaner can penetrate into the contacts. Sometimes it's easier to pull the knobs off and spray from the front. "Torture" all the switches afterwards with repeated pushes to do a good cleaning

[FranLab]

Yea - Fran's vintage gear troubleshooting step #1: Clean all contacts.  :-)

[SaturnV]

Important also to note - Yes, "wiggle" (wig for short) is a measurable quantity . . . the physical displacement of an electrical conductor (wires in particular).

Follows standard notation . . . 1000 milliwiggles (milliwigs) = 1 wiggle   
1000 wigs = 1 kilowig

[rbarkoch]

Even without a crazy interesting issue, these repair videos are great and give a great perspective into the design of the product, often times even more than a regular teardown. Keep them coming!

[TonyKDRTT]

Dave, just want to say I appreciate this type of video. I know it's a lot of work to do repair videos, but I really enjoy them!

[BillyNoMate]

It doesn't matter what the outcome of these repair videos, they are a great troubleshooting resource. (y)

[fagear]

Hi Dave.
From 1:35 and I could not think of anything except those switches...
They look very similar to USSR "П2К" series that are known to have issues with wear and oxidation. I didn't find any video about repairing them, so I've shot my own (/watch?v=lieYhz3ICo8)
Voice is Russian (of course, I am in Russia), but I've made English subtitles for the video.
Probably after you watch it you can refresh all those switches and be confident in that DMM.

BTW, in Russia we use those "funny plugs" also. We call them "european plugs". ;)

[MrOffizier]

If I have to fix something I go strictly through my list:

1) Check for mechanical issues
2) Check PSU (eg voltages)
3) Check for bad caps/burnt objects (you can take a quick look before step 1 and 2)
4) Check the rest

No. 1 fault -> mechanical
(Ok, if you repair monitors/tvs, it's like always the caps)

[littlebushfarm]

Dave, my son is just getting started into electronics (he's only 8 but we're making progress), at the moment he's got a $6 meter from Jaycar!!!! It would make his day to be the proud owner of this...I've got a sister in Melbourne that is heading back to NZ soon so it makes postage simpler.

Cheers


edit:Ah, too late...such is life!

[Tjita]

That's a European Schuko plug. We use 230 V in Europe. :)

[CrucialSpeaks]

clean switches.. Blue stuff if you have it, polishes too.
GREAT VIDEOS! from a 45+ year component level technician with 48 certifications and vice president of CESDA (sub of NESDA) in 1980- 1983!!

[managementrights]

Perfect at 36:20 David reveals the fault in the physical contactor, inspection and diagnostic technique plus experience is good

[KX]

I was shouting at the screen that it was the ganged switches from right at the beginning of the video when it was failing and then coming good almost only when you pushed a button. I think that's because I'm watching and not doing so I could pay more attention to things like that. It helps to troubleshoot with someone else.

I really didn't expect to be right though because of the counting up numbers I didn't know how a dodgy switch could do that until you explained at the end. I then thought it was going to be the integrator, especially when the zapped resistor was in the vicinity of the ADC testpoints. When you looked at the schematic showing the blown resistor in circuit and I saw the ohms switch above it I again suspected the switches.

I'm right about these things so rarely that I'll be walking around with a smug smile all day.

[DoItYourselfMusician]

Who else was screaming "Clean the switches Dave!" for like the first 40 minutes? Pro tip, you can drill a small hole in the top of those gang switches to get cleaner in them.

[reallyniceaudio]

I just fixed my 179A which had the same fault. If you turn the unit so the front is facing down you will notice your can squirt down a whole in the back of the switch! I then did a transfer cal from my 2015 and have managed to get it to match perfectly. I am so pleased with it it has replaced my silly isotech idm 203 as the screen on the 179A is amazing!!

[jerryfox]

I learn from every video you make. Old or new. Whether it jump at you or not. Because that is real life. Thanks for all you do. keep up the great work.

[wheelitzr]

That was a perfect example of how something small like the blown resistor can really narrow your way of thinking and make it difficult to diagnose something because your brain is hung up on that one part. Excellent video I'm glad you put all that footage in.

[direchannelstream]

ive exactly the same problem with the same model. sprayed the contacts now with contact cleaner and let em dry overnight.
(next day)

well and now after 8h drying its working perfecty.
thank you dave. you rescued at least one more unit with this video;-)