Annoying click when touching a couple of keys on 42S

[Dave Britten]

I've got a 42S that I use daily, and it's developed a habit of making an annoying clicking sound when a couple of the keys are touched even lightly. If I firmly press the key and rock it back and forth a bit, this often silences it temporarily, but the sound usually comes back within the day. This is not like the issue with Indonesian 32SIIs where there's a loud popping sound when releasing certain keys, it happens when the key is lightly touched, and not even pressed. Is there a known fix for this? Should I inject a small drop of something around the key to clean it out? (Distilled water, plastic-safe oil, etc.)

[SammysHP]

I might have the same issue with my 42S after I had to disassemble it completely. While I assembled it again, I tried to compress the membranes and backplate as hard as possible while applying the epoxy to the plastic staking pins. But I think it was not enough and now you can hear these clicking noises when you touch the keys. I think it comes from the key making contact with the plastic sheet. If everything is compressed enough, the key makes permanent contact, so you can't hear it.

[GreyUser]

If something was spilled into/on the keys, pop/cola/soda/coffee/tea, basically anything with sugar can form a sticky layer between the actuator pin of the key top and the dome sheet, causing an annoying click. The test is a light touch, if this results in noise, it’s probably crap between the pin and the dome.

Remove the batteries and start with distilled water, a couple of drops on the key(s) in question, operate the keys, repeat. If it’s really bad, a full immersion in warm distilled water is a good way to clean, press all the keys while submerged, drain, press keys, repeat. This process flushes the domes and cleans things about as good as you can get.

Shake all water out, repeat until you can get no more water out/off. Allow it to dry over night in a warm place with an air flow over it before reinserting the batteries. If you see any wonky behavior, numbers or operations appearing you didn’t press, get the batteries out of it immediately and leave it to dry. Don’t be in a hurry, if you shove the batteries back into it while there is any moisture in the area of the ON traces, you can open the traces via electrolysis which is a royal pia to fix. There is no risk of damage so long as you don’t leave batteries in a wet or even damp unit. Dry is safe, wet is not.

[Raymond Del Tondo]

I think the hardly-press click sound comes from a partly torn or sticky membrane.
I heard that sound from all HP calcs using plastic membranes, from the HP-41 to the HP 48.
It sounds like a broken membrane, and so it may be in many cases;-)

[Dave Britten]

Thanks for all the tips. It doesn't sound like a broken membrane, but I certainly can't rule it out without opening the calculator.

For starters, I'm going to inject small amounts (0.05-0.10 mL) of distilled water around the offending keys and work it in through use to see if that cleans out whatever sticky residue might be in there. I know it's not going to be completely removed without a full immersion in distilled water, but I can live with at least washing it to someplace that doesn't interfere with the key action.

[GreyUser]

It’s not a broken membrane, the plastic domes in the pioneers and 48’s don’t break or crack. They can become flat, that is they can lose their spring tension/snap/tactical feedback but that is not a broken or cracked dome. And yes, they can audibly click as seen with the units that appeared later in the pioneer life cycle but these were due to changes in manufacturing, most likely when the volumes were significantly reduced. The dome sheets that are really bad click even when out of the calculator.

Some of the last batches of 42S service replacements made in Indonesia did have a few of the annoying clicking keys but that’s got to be a really small sample size, in comparison to number of units made in the US and Singapore.

On the other hand, the metal domes used in the redesigned spices, the 41’s and the the voyagers can indeed crack, although it’s pretty uncommon. The most common failures of those units is for the keytops to fracture where the projecting flat part of the hinge meets the body of the key.

As for your 42S, clean it and it should be fine.

[Massimo Gnerucci]

(05-11-2020 08:14 PM)GreyUser Wrote:  Some of the last batches of 42S service replacements made in Indonesia did have a few of the annoying clicking keys but that’s got to be a really small sample size,

Uhmmm, must check my ID027027** 42S