Author Topic: Bringing a dead-display Keithley 169 Back to Life  (Read 222 times)

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Offline fivesixzero

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Bringing a dead-display Keithley 169 Back to Life
« on: June 16, 2021, 10:49:53 pm »
A few months ago I came across a lonely, dejected, mute Keithley 169.



Its history was what hooked me at first, since it came with some data attached to it indicating that it was once owned by Northrup, an aerospace company. I like airplanes and spaceships and Northrup worked on both of those. So I was into it.



After giving it a good scrubdown and removing its long-corroded "C"-cell batteries I gave it some juice to see if it'd show any signs of life on its flooded display. Some flickers revealed signs of life under the surface! Its alive!



Some careful probing with a scope revealed that, indeed, this little guy is still trying to talk to the world, broken display be damned. Poor little 169. :(



Taking a closer look, I could see a familiar looking IC on the board, even if it was going by an unfamiliar name. While ITS80041 was unknown to the interwebs, another post on these very forums revealed its true name to me: ICL7106.



Although its pins may be reversed, as it looks to be the less common "R" variant of the ICL7106, it couldn't hide its secrets any longer. I set to work prototyping a replacement around an TN display from Digi-Key. (sadly no longer available only a month later)

After years of pained silence, the 169 can finally do what it was built to do! Display a number!

Behold!



Although the display is too large to fit, it was a fine start for a proper prototype. A board was drawn up in KiCad and ordered from the kind folks at PCBWay.



This board worked, but its dimensions were all jacked up. The display was too big to fit into the panel and the board's mounting points were way off, like 10mm off.

Even if it could speak now I could tell the poor fella just wasn't happy. Another round of prototpying would hopefully do the trick.

So, on to version two. A more appropriately-sized, althought still not perfect, LCD panel was selected. The board was redesigned to actually match measurements for mounting points. And, for good measure, some extra pins were made for test points for future experimentation.

And it worked!



And now our friend, Keithley 169, is mute no longer. Its free to roam on the bench, all tuned up and ready to play with its newfound friends. Here it will live, regularly calibrated and well fed, happily ever after.



...

This was a fun project that gave me a good low-stakes excuse to learn KiCad for a super-easy board layout. Currents on the order of 0.1A, 5V 50 kHz square waves, and no parts beyond the panel and the pins. I'll admit it was a bit of a thrill to get that first pile of PCBs, all made to my specs with my layout and my mistakes. Small moments of joy, but I'll take em. :)

Although the 169 is definitely not Keithley's finest product I developed an affinity for it while working on this. And it led me down some really fun rabbit holes like the crazy history of DMMs/DVMs and the wild stories about the origins of the absurdly long-lived ICL7106 family of chips.

I had never realized how important the late 70's were as an inflection point for consumer electronics tools. I still don't have the full picture, but reading dozens of issues of Electronics, Popular Electronics, and other old magazines was a delightful diversion in an otherwise very challenging time in my life.

Anyway, I've put together a GitHub repo containing the board files along with a brain-dump of the historical context I gathered and some of the clippings  of Keithley 169 ads from several publications.

https://github.com/fivesixzero/keithley-169-display-replacement

I'm hoping that other people are inspired to bring these lovable little rascals into their lives and keep them from filling up landfills.
« Last Edit: June 16, 2021, 10:57:20 pm by fivesixzero »
 

Offline fivesixzero

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Re: Bringing a dead-display Keithley 169 Back to Life
« Reply #1 on: June 16, 2021, 11:07:02 pm »
Some fun historical ads for people who might also be into that kind of thing.

Keithley 1979 DMM lineup ad (169, 172A, 173A, 177, 179, and 191), Electronics Magazine, July 1979: "Buying too much DMM makes some people feel secure"

Keithley 169 ad, Electronics Magazine, August 1979: "You've pinned your last needle"
 

Offline lowimpedance

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Re: Bringing a dead-display Keithley 169 Back to Life
« Reply #2 on: June 16, 2021, 11:49:18 pm »
Nice job and write up  :-+............and another old timer rescued.
I have a Keithley hand held model 131 which uses the same reversed ICL7106, which had died so I wired a standard one in dead bug style  :P

Interesting ad, which model was the most popular I wonder.
« Last Edit: June 16, 2021, 11:57:08 pm by lowimpedance »
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline fivesixzero

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Re: Bringing a dead-display Keithley 169 Back to Life
« Reply #3 on: June 17, 2021, 03:24:17 am »
>I have a Keithley hand held model 131 which uses the same reversed ICL7106, which had died so I wired a standard one in dead bug style  :P

Ha! That's awesome. Dead-bug definitely seems like the way to go with replacement of these "R" type ICs. I've been thinking about trying that out with a modern pin-compatible variant like the ICL7136 or even the fancier stability-enhanced MAX130A just for kicks.

I've been curious about the 130/131/128 family of 3.5-digit DMMs tho. The 169's odd place in the market and relatively short longevity didn't make much sense to me at first. But when I started thinking about it as a kind of marketplace gap filler and development exercise for the upcoming 130 family it made a bit more sense. In a lot of ways that matter, the 130 and 169 seem to be almost identical aside from the massive 1 year plus battery life of the 169.

Also, it seems like building the 169 first allowed them to bring a device to market very quickly to fill that low-cost niche by reusing the same chassis parts as their other DMMs. The 'industrial design' is pretty much identical to its more expensive LED-display siblings. By getting even a marginally competitive device on the market they could take more time to cost-optimize the very un-Keithley casing of the 130. The extra space in the 169's case also gave them a huge amount of room for batteries (6x "C" batteries instead of a 9V) too. This gave their marketing teams the weird selling point of a 'portable' meter that only needed its batteries replaced once a year at calibration time, which they actually mentioned in a few ads.

I'm guessing that alone wasn't worth it for most people or institutions Keithley tried selling it to though. I guess this was fine since the 130 came along not much later to fill those gaps. Ads for the 169 seem to have peaked in late 1979 and dried up completely by mid-1980, just as the 130 was picking up steam...

I am curious though whether there were any major differences in the analog front-end designs or component selections of the 169, 130, or 131, or if they were basically identical. I haven't seen a 130/131/128 on eBay or at my local surplus stores at a price in the "just to satisfy my curiosity" range just yet, but that curiosity keeps getting curiouser. :)
 


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