Some of the 80’s HP/Agilent Test equipment uses this pushbutton switches (HP P/N 5060-9436), which may get quite hard to push, with a nasty feeling of being stuck and then released with a loud sound, like those clickers used to train dogs. I happen to have a few instruments with the same hard-to-press buttons, such as (5370, 8904, 3586) and decided there should be a solution.
This is how this type of buttons look like:
On each button, there is a steel strip, used as detent spring that may be susceptible to crease and, in the worst case, pop out of the switch assembly. If you look carefully while you press one of this worn out buttons, you will see that the steel strip tries to flex agains the plastic surface on the zone “b” in the picture. Since there is no way to move in that direction, the strip is badly compressed until it pops out to the other side (up).
What we want is to slightly curve the strip up, so that it starts to move up smoothly right from the begining of the action, as shown at the end of the video.
The strip can be removed vertically or horizontally, depending on the clearance around the switch. I am showing the vertical procedure, which is the most tricky. The horizontal is very straightfoward, simply slide it out, correct the shape and slide it in again. Do not use the tweezers to curve the strip, use only your fingers. If you try to bend it in a too small radius, it will collapse and break. The strip may also have developed an undesired curve in zone “a”, which we should revert back to straight as possible to recover (what I believe it was) the original feeling of the button.
I’ve found various HP service manuals describing this issue and suggesting to replace the defective switches. That is, if you can get them!