The Cutest Tektronix O'scope (Patreon)

Meet my new old Tektronix 222. It's a classic early digital scope from 1988. At 2 channels, 10 MHz, 8-bit sampling at a rather pokey rate, it's not a screamer even for the time (my monster Tek 7854 samples to 10 GHz!). But it's so small and portable and easy to use.  The CRT display clocks in at an adorable 2" wide, extremely sharp and constrasty. And, imagine that, it's a battery powered CRT scope! But foremost, it's just so puppy-cute you'll want to adopt it.

Even in this age of cheap LCD scopes, there really isn't anything that compares, particularly in terms of build quality and ease of use. Of course, this is because it was a very expensive instrument back then. The front panel layout, with real knob controls where it matters, is a delight to use. Tek's are always superb in this category, but this one is so simple, yet so intuitive and functional, it deserves an award. 

Unfortunately I'm not the only one to think that, so even non-functional or untested units are not cheap, likely costing more than the modern cheap Chinese LCD scope equivalent.

Mine was of the "unable to test" category from eBay. But it arrived in very good condition. Formerly from Delta Airlines I think. It was only missing a knob and the external power supply. However it had the all important special impedance probes, the carrying case, and even the RS-232 manual, which I have now scanned.

Look, it's afraid to come out, hiding in its padded case.

The lack of a power supply is no big deal, since it's extremely tolerant of any power input: 12 to 28V DC, or 16-20V AC, only 15W. An old 20V laptop supply did the trick.

And it turned on! It almost worked. The only fault I could see was that the horizontal position and speed would not work. The position knob somehow moved the speed instead of the position, and only haphazardly across a few ranges. The range knob did nothing. The x10 push-button action did nothing, it did not even click in. These are all part of a multi-function knob at the bottom right. I suspected mechanical foul play. 

So in we go. Ooh, aah, the mini CRT screen. The unit was super clean also.

The multi-function knob is actually a modular stack-up of a rotary encoder (for hor. speed), a pot (for hor. position) and a switch (for x10). They were very tricky to take apart.

I soon found a possible culprit. This circlip at the end was bent and out of position, and the whole middle shaft (for the pot) had been pulled forward. It rammed the rotary encoder and partially damaged it. 

I was able to fix it though, after some watchmaking-like work under the microscope. After reassembly, everything seemed to work properly. But when trying to run the channel self-calibration, I got this ominous FAIL message:

I could not make sense of the fault. From the error codes, the service manual was telling me to replace the acquisition board, but I could see it was working properly, both channels displayed the signal correctly. And also I got similar error codes when calibrating both channels, but could not locate on the schematic something common to both that would do that. While I was at it, I did the other adjustments, which included performing the very nifty screen alignment:

After that realignment, I was explaining on video how I was going to give up because it worked good enough, when it suddenly passed while I was blabbing into the camera. I didn't even realize it at first.

I'm not sure if my screen adjustment helped - I don't think it should have. Anyhow, I can use a miracle once in a while. 

The scope has now taken the little spot I had earmarked for it on my bench. I wanted an "always on hand" scope to do first line troubleshooting before bringing in my Agilent/Keysight scopes which always disappear somewhere else - and take much more bench space.

We'll keep it. It's been adopted.

Marc