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-replacementI'm hoping that other people are inspired to bring these lovable little rascals into their lives and keep them from filling up landfills.