Agilent 54622A intensity knob shaft - Page 1
Forum section: electronics / testgear

author: rdenney
author_rank: Regular Contributor
timestamp: October 08, 2025, 03:24:56 pm
content: The intensity control is a pot mounted on the PCB that controls the CRT section of the 5462x-series scopes. Mine has a typical problem--the knob is broken off. The knob is glued to a plastic shaft that fits over the shaft of the pot about three inches behind the front panel. That plastic shaft is shaped with opposing annular clips near the knob which snap into the front panel. In theory, pulling the knob unsnaps those clips, allowing the shaft to be wiggled around out of the front of the unit.This issue is also discussed in this thread, with pictures:https://www.eevblog.com/forum/repair/agilent-54622d-missing-intensity-knob/The shaft on the scope of one of the respondents to that thread broke in the narrow section right in the middle, and it fixed it by gluing the two ends into an aluminum tube. Mine didn't break in so convenient a spot.Or, maybe the knob isn't glued to the shaft, and mine just became glued somehow. Attempts to remove the broken-off part from the knob have failed--the shaft broke right at the base of the knob and even tapping a screw into it and pulling it didn't work. Further attempts will just ruin the exterior of the knob. In addition to the shaft on my scope being broken right at the base of the knob, it is also cracked where it goes around the shaft of the pot, and to my thinking trying to restore the plastic part will not result in a reliable repair.My plan is to machine a new extension shaft from aluminum, with a screw collar that clamps it to the shaft of the pot inside the unit. That way, it would not need to clip into the front panel at all. Then, I'll drill a hole in the knob that will fit over a turned-down and split section of the aluminum by friction. That should be a fairly easy few minutes in the lathe and mill.The question is:Should I be worried about using aluminum in this application?This is at the lower left corner of the scope case, about an inch from the corner of the CRT (see pic below). The intensity pot has a plastic shaft with a D section, so a screw through the side of an aluminum collar bored to fit the diameter would clamp onto the flat part and secure everything. The screw would be easily accessible to being loosened after removing the cover of the scope. I don't think the aluminum can contact anything that would energize it, and I can't imagine that it would have any other effect. But I'm open to comment.(image linked from:https://neuron.eng.wayne.edu/auth/ece3310_OLD/oscilloscope.htm)Rick "thinking plastic was not a good design solution for this vulnerable knob on a portable scope" Denney

author: yo0
author_rank: Regular Contributor
timestamp: October 08, 2025, 05:04:13 pm
content: https://www.thingiverse.com/thing:4609646Best regardsPio

author: rdenney
author_rank: Regular Contributor
timestamp: October 08, 2025, 05:41:57 pm
content: Quote from: yo0 on October 08, 2025, 05:04:13 pmCool! I wish I had a 3D printer.But I do have a lathe and a mill, and really I think aluminum would be more durable. But if I had a 3D printer, this would be the easy button for sure.Rick "thanks" Denney

author: rdenney
author_rank: Regular Contributor
timestamp: October 12, 2025, 08:24:57 pm
content: I need to get a 3D printer. But what I made has worked perfectly, even though it required tooling a lot more of a rabbit hole than a 3D printer. But I’m already way deep in that machinist rabbit hole. For this project, I used a South Bend 14-1/2” lathe and a Bridgeport milling machine, but a hobby large, a file, and a drill press would have worked well enough.Starting with 1/2” aluminum round bar, I made two parts—a coupling collar and an extension shaft. It’s facing down in the pic, but the collar has a milled flat with holes drilled and tapped for 4-40 lock screws.Here they are installed. Being serviceable was a requirement, and loosening the two lock screws holding the extension shaft allows that shaft and knob to be pulled out of the front panel. The salvaged knob is a very tight fit, and removing it with the shaft is the easy way.The pic above also shows the new PCB battery I installed. That allowed me to recalibrate the scope.Here’s the scope back together and working perfectly.Rick “looks more like a shaft in a cold-war-era Tektronix” Denney

author: yo0
author_rank: Regular Contributor
timestamp: October 13, 2025, 12:51:53 am
content: Congratulations!! Very good work, now just need to upgrade the software version to the latest one,Iirc to version 2.31You just need a good disketteBest regardsPio