Vintage HP15C Key Clicks but Doesn't Register

[Bruce Zastera]

Sometimes if I press the "1" key too lightly on my vintage HP15C, it clicks but doesn't register the number, but it will register it if I press a little harder. The other keys all register when they click. Anyone know of a fix other than trying to replace the keypad?

[David Griffith]

Maybe there's crud underneath the key interfering with the contacts.

[Bruce Zastera]

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Maybe there's crud underneath the key interfering with the contacts.

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If that's possible, that's likely the problem since I dug out massive amounts of crud with a dental pick from around the keys. From pictures I thought that the contacts were sealed. My pc board appears to be held on with a lot of heat stakes, so I guess I can't make progress without a lot of effort which could cause more problems than it would solve.

[bill platt]

Search the articles forum and also this forum for stuff on cleaning keyboards. ook fr Randy Sloyer's posts. Also for Geoff Quickfall's. Sometimes you can actually soak the whole machine in water! (With batteries out).

[Bruce Zastera]

I may have fixed it. I found this post by David Smith:

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv010.cgi?read=26479

I put a drop of 91% isopropyl alcohol in the hole and scraped with a few strands of wire like he says. That didn't fix it, but then I used a dental pick. It took a couple of tries, but the "1" key seems to be working consistently now, at least for the time being. It still feels a bit softer with less of a click than the other keys. The "4" is a bit soft too, but not causing a problem. At one point while I was screwing around the ON key stopped working. Not sure what that was about, but it all seems OK now. Never in a million years would I have thought of this or thought that would ever work. Thanks David.

Speaking of keys, what is the status with the key problems on the LE? Will the next run have any fixes? I saw a youtube video where the f and g keys were very loose. It looked unacceptable to me, and I have one on back order.

[Geoff Quickfall]

i was just typing the explanation when you posted. The spongy feel may vanish as the alcohol evaporates.

A better then alcohol result will occur if you purchase some DeOxit gold and introduce a tiny amount of it to the hole. Use a soft wire next time and not a dental pick as it can puncture the dome used to create the click and positive contact.

Cheers, Geoff

try with the gold first then step up the cleaning with the wires.

[Kees Bouw]

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A better then alcohol result will occur if you purchase some DeOxit gold and introduce a tiny amount of it to the hole.

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There are many types of DeOxit Gold, for example on www.deoxit.com. Can you be more specific about the exact product to use?

[Geoff Quickfall]

Small tube, have to look for it. The small tube is excellent as you can trim the tip flat, place it over the hole and gently monitor the amount you introduce.

The key will feel soft depending on how much you insert but that will diassappear over time.

It is wonderful on hp 41 bouncy keys too.

Geoff

Edited: 28 Jan 2012, 2:33 p.m.

[Bruce Zastera]

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Small tube, have to look for it. The small tube is excellent as you can trim the tip flat, place it over the hole and gently monitor the amount you introduce.

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Here is a tube. They also have this can with a long applicator tube that I thought would be good. Which is better?

My "1" key has been working perfectly now for 2 days. I didn't even use the Deoxit yet. I stripped a solid copper wire that was the same diameter as the via hole, put 91% isopropyl in hole and on wire, inserted wire and turned it while holding key.

It makes sense to use a non-metalic brush though as that would have a better chance of sticking to and removing the debris. It might also be less likely to cause damage. Perhaps one can place lips over via and provide a suction.

I may have to repeat the process for my Enter key. It may be my imagination, but it feels harder to press now. It ocassionally doesn't register, whereas I never noticed that before. I don't know how I could have affected that key unless I used too much isopropyl and some debris floated over there.

[David Griffith]

The shift keys on my 15cLE are noticably looser than the other keys, but it's nowhere near being annoying... and I tend to get annoyed by stuff like this.

[Bruce Zastera]

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The shift keys on my 15cLE are noticably looser than the other keys, but it's nowhere near being annoying... and I tend to get annoyed by stuff like this.

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Is it as bad as this? Or this?

[Marcus von Cube, Germany]

Mine resembles pretty much the second video, but, as David already stated, it's just not annoying at all.

[Jeff O.]

My two units are wobbly, but not as bad as either of the videos. I don’t mind it and I am also pretty picky about such things. You originally asked "Speaking of keys, what is the status with the key problems on the LE? Will the next run have any fixes?" If you are hoping that the f- and g-key wobble will be fixed, I'm pretty sure you will be disappointed. The basic physical design of the calculator results in those two keys being more wobbly than the others. It is probably unlikely that HP will redo the basic design to eliminate this effect. As for the problems with keys not registering when pressed that were reported with the initial run of calculators received back in September, those problems seem to have been fixed in later shipments.

[uhmgawa]

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..the "1" key seems to be working consistently now, at least for the time being. It still feels a bit softer with less of a click than the other keys. The "4" is a bit soft too, but not causing a problem.

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IME there are two common problem scenarios with the legacy voyager
keypad. One being the ingress of contamination into the snap dome
vent holes. Solvent soaking and/or probe scraping will probably
move some of the contamination around, potentially away from the
vent hole contact area and improve the situation. But I'm
doubtful it actually flushes substantial contamination out of an
individual snap dome land. Still if I had one or two problem keys
I'd try to loosen up any contamination using a fine bristle
brush twist-inserted into the via vent and then mushroomed out,
add a mild solvent in the vent via, press down on the dome as
the brush is worked/extracted to increase scrubbing pressure
to loosen up the contamination. The vent holes are about 1.1mm
in diameter.

The less welcome problem is keycap actuator wear-through of the
elastomer membrane located over the snap dome array. Tactile
domes are designed to be inverted by a probe in their center,
sized relatively small compared to their diameter. This is
required to minimize the inversion stress and maximize service
life, minimize inflection force, and results in a sharper tactile
snap. When the ~1.2mm probe in each keycap eventually wears
through the membrane it creates a puckered bump which greatly
increases the pressure area applied via the key. This is the
reason addition force is required to inflect the dome and causes
the "mushy" feel. Repair of this is only possible via replacement
of the membrane. That's almost the good news as finding a
replacement realistically means cannibalizing another voyager
or attempting to create a replacement membrane. The original
is ~0.45mm thick so 0.5mm sheet may work given the heat stakes
are to be reset/glued under pressure. Accurate punching of
holes in the elastomer blank could be accomplished via a 1/16"
ID tube sharpened to a hollow cone using a drilled plate as an
alignment guide.

[Bruce Zastera]

Dammit. It was working perfectly right after I cleaned it last night, and today it is worse than ever. I'll try to find the DeOxit stuff.

Edited: 27 Jan 2012, 5:31 p.m.

[uhmgawa]

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Dammit. It was working perfectly right after I cleaned it last night, and today it is worse than ever. I'll try to find the DeOxit stuff.

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Until it flashed off the isopropyl may have softened the
contamination sufficiently allowing the dome to displace
it when depressed, permitting electrical contact.

FWIW I've actually never encountered a voyager snap dome
PCB land with worn gold plating. So it is difficult to
predict whether it may be copper oxidation or surface
contamination without further disassembly.

Whatever goes into that vent via which successfully
dislodges contamination (or dissolves oxidation) needs
to be removed as it is only going to hold it in
suspension until it evaporates.