I acquired my brother's radio collection when he passed away a few years ago.
Recently, (thanks to covid) I starting to become active in the hobby again.

That being said, one part of my brothers collection is a Jackson 648 tube tester.
I don't know if it works or not and it appears to need a little bit of cleaning, etc.
Before I went whole hog on cleaning/restoring this item, I wanted to ensure that everything is working as designed.
This is when I noticed that there were some mechanical problems.

What I mean is - For example, Tube 37 states that circuit D should have buttons A, B, C depressed.
The problem is that when I try to push the 3rd button down, the other 2 pop-up regardless of the order that I press the first (2) buttons.
Note: This happens for both circuit D and E push buttons.

Also, I am of the opinion that everyone knows more than me, so if anyone has any suggestions on how to troubleshoot/repair - I am all ears.

Thanks!

Im not sure about the ABC buttons all pushed at the same time on the original 648, but on the 648S these buttons can all be pushed at the same time, though I dont think Ive ever seen them called for on the D circuit. According to my roll charts the 37 tube calls for 123 pushed for D circuit.

You are correct about the 123 buttons.
Don't know what I was thinking when typing the question.
Basically a disconnect from brain to keyboard.

That being said, your suggestion on pushing all the buttons at once does work.
My concern is that 'sometimes' they pop-up when I push buttons for Circuit E.

Since I don't have any experience with these types of devices, I didn't realize how sensitive that they are (or maybe just mine).
Anyway, I'm going to assume that this is normal for these devices and not try to fix something that is already working (well enough).

Thanks for the timely response.

The pushbutton assembly, and others of similar design, are meticulously methodically made mechanical marvels making me mull more and more why they still work at all, after all this time. (ran out of "m" words, sorry, although I did try to work mediocracy into it).

Sometimes they need to have the mechanics cleaned and lubed, as well as the switch contacts. Obviously the method for restoring the two different parts of these switches is much different. Also, sometimes a part of the interlock system may bend, or even wear to the point that they don't work anymore. Since they are unobtanium as replacement parts, keeping them working properly (not sticking) is important to NOT having something wear out.

I started once looking into making a relay based replacement for the Hickok 539 type interlock switch assy, but quickly gave up in frustration. It's complicated. I may get back to this some day if there seems to be a need.

If you're not familiar with how to do clean and lube this type of interlock switch, it might be best to have someone go over the tester that has the necessary experience, or practice on some other device that isn't as important or may be otherwise beyond repair. It requires some fine mechanical skills and a knowledge as to what needs to be lubed, and what does not. In this case, possibly no lube needed.

Excellent use of the word 'unobtanium'.
Motivated me to go look it up

FYI, I am a member of a club (Mid-America Antique Radio Club) in the KC area and have approached a few people about this topic.
Hopefully, that will yield some results/ideas.
If not, I am still planning on using the unit with the understanding that it will be a little finicky.

Have a Great Day!