New power button for old analog Tektronix scopes? - Page 1
Forum section: electronics / repair

author: Freesurfer
author_rank: Regular Contributor
timestamp: March 11, 2025, 12:05:17 am
content: The power button of my old, reliable and beloved Tektronix 2221 has broken so that I need to hold it in to power on the scope, but doesn't remain in when I release the button.Before I "take it apaaaaah't" to look for a solution, I am wondering if anyone knows if the power switch is an easilly obtainable off the shelf part, or if I will need to hack something together. In the worst case I will just bridge the power switch and put a switch on its power cord or something.Here's an online web page with a photo of the scope. I am sure many other Tektronix CRO from the era use the exact same power button:https://w140.com/tekwiki/wiki/2221

author: bdunham7
author_rank: Super Contributor
timestamp: March 11, 2025, 12:54:43 am
content: The switch is in back and is activated by a long plastic rod. The original Tek p/n is 260-2443-00, that was made by ITT Schadow, p/n 130-238. I think the modern replacement is from the C&K NE-18 series, perhaps this one:https://www.digikey.com/en/products/detail/c-k/NE18CTII-2A-EE-SN-P-4AMP/2043276Or just click on the datasheet and see if you can figure out which one matches up exactly with what you have. If you have limited choices, sometimes trimming off leads from a DPDT switch or one with unneeded top terminals will work.

author: benj38
author_rank: Frequent Contributor
timestamp: March 11, 2025, 03:32:05 pm
content: In this type of switches, the thing that holds the switch position after you release your finger pressure is that steel wire that looks like a piece of a paper clip partially underneath the spring in the images of the part that @bdunham7 has linked to.In my experience, with this symptom, this piece of metal simply jumped out of place more often than any more serious problem (like broken/chewed plastic grooves where this metal piece engages).I suggest you open the scope up to see if you can fix it before you start hunting for a replacement part.

author: Freesurfer
author_rank: Regular Contributor
timestamp: March 12, 2025, 10:44:42 am
content: Ok, thanks. I didn't know there was a rod from the front to the back, hopefully that makes the switch easier to access without taking the mainboard out.After pushing the button repeatedly I was able to make it latch in the on-position, so for now I'm just leaving it like that and not touching it.But I will look open it one day and look into that into that spring mechanism, and also those C&K switches if a replacement is needed.Thanks for the help and suggestions

author: ondraN
author_rank: Regular Contributor
timestamp: March 12, 2025, 12:20:37 pm
content: It's quite "fun" to get to the power switch on this oscilloscope. You have to first flip the top mainboard, which means disconnecting some wiring and removing the knobs from all the switches on that board. And then there's a steel cage covering the power supply, but I don't remember if that also has to be removed to access the power switch, but I think so.

author: Manolo Mos
author_rank: Contributor
timestamp: March 12, 2025, 06:11:07 pm
content: Maybe if you put a little lubricant oil in the switch the problem get off.

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 13, 2025, 02:10:13 am
content: Yeah, often the grease in the switch goes hard causing the parts to get stuck.A clean and relube often has them all fixed.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 13, 2025, 03:24:20 am
content: If I might piggyback on this topic a bit, my Tek 475 has a broken knob, the outer knob of a concentric pair (slope level).Where does one look for such replacement parts (besides eBay, where the going prices strike me as pretty ridiculous)?

author: bdunham7
author_rank: Super Contributor
timestamp: March 13, 2025, 04:42:06 am
content: Quote from: Analog Kid on March 13, 2025, 03:24:20 amIDK what prices you are seeing on eBay, but if someone goes to the time and trouble of breaking down an old scope, packaging one knob and sending it to you I'd think $20 or so wouldn't be ridiculous. You don't find them at the dollar store in the clearance bin...I presume you've looked it up and see that it is p/n 366-1280-00. Sphere is out of business and Q-Service doesn't have any right now. You can go beg on Tekscopes or Tekscopes2 @ groups.io, maybe someone has some laying around. Or you can print your own:https://www.thingiverse.com/thing:6777734Or maybe someone here will part with one.