After extensive use: The keyboard

Discussion about the new DM41X calculator
cdmackay
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Re: After extensive use: The keyboard

Post by cdmackay »

yup, this is my only annoyance with what are otherwise wonderful devices.

I've even fitted replacement keyboard "foils" to both my DM42 and DM41X, with a clean of the contacts (and the foil); the DM42 improved enormously, the DM41X not at all, which suggests there's more to it than just that…
Cambridge, UK
41CL/DM41X 12/15C/16C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 32SII 48GX 50g 35s 30b/WP34S Prime G2
& Casios, Rockwell 18R :)
jonmoore
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Re: After extensive use: The keyboard

Post by jonmoore »

cdmackay wrote:
Thu Jun 04, 2020 9:06 pm
yup, this is my only annoyance with what are otherwise wonderful devices.

I've even fitted replacement keyboard "foils" to both my DM42 and DM41X, with a clean of the contacts (and the foil); the DM42 improved enormously, the DM41X not at all, which suggests there's more to it than just that…
Strange. Since I had a thorough clean inside a week ago (and loosened all the keys), I haven't had a missed key-press since. Not sure how long things will stay this way but I added putty strips in concentric rectangles to stem the flow of nuisance making muck. I'm hoping this second line of defence will help keep the contacts clean.
cdmackay
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Re: After extensive use: The keyboard

Post by cdmackay »

thanks Jon.

I'm trying to work out what the problem could be.

In my case, I can most easily reproduce the issue by pressing gently on the key. By modulating the amount (of lack of) key pressure, I can reliably, repeatedly, get a firm "click" feel from the key, but with no keypress registered by the calc. Pressing a little harder makes no difference to the feel, but does reliably register.

That suggests to me that the foil dome is "clicking' down, but not coming into contact (or enough contact) with the board under it.


Oddly, after replacing the DM42 foil, cleaning foil and board, and bending the keys, the result was amazing: a quite audible click, and no missed presses. A massive difference, I was delighted.

But doing the same with the DM41X made no difference at all.

I'm at a loss how to explain that. I'm also not clear on how "bending" the keys helps, although I did it in both cases. I can see flexing the keys changing their default, no-press position, but not how it changes what happens when I press on them?
Cambridge, UK
41CL/DM41X 12/15C/16C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 32SII 48GX 50g 35s 30b/WP34S Prime G2
& Casios, Rockwell 18R :)
cdmackay
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Re: After extensive use: The keyboard

Post by cdmackay »

jonmoore wrote:
Thu Jun 04, 2020 9:18 pm
Strange. Since I had a thorough clean inside a week ago (and loosened all the keys), I haven't had a missed key-press since. Not sure how long things will stay this way but I added putty strips in concentric rectangles to stem the flow of nuisance making muck. I'm hoping this second line of defence will help keep the contacts clean.
Also…

the electrical contact is between the underside of the foil dome, and the board, surely? Since the foil is firmly stuck to the board, how are the contacts getting dirty?

I can see dirt attaching to the top of the foil, but that contact is purely physical, between the key and the top of the dome, and I don't see how a bit of dirt would make any difference there?
Cambridge, UK
41CL/DM41X 12/15C/16C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 32SII 48GX 50g 35s 30b/WP34S Prime G2
& Casios, Rockwell 18R :)
EM41
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Re: After extensive use: The keyboard

Post by EM41 »

cdmackay wrote:
Thu Jun 04, 2020 10:40 pm
the electrical contact is between the underside of the foil dome, and the board, surely? Since the foil is firmly stuck to the board, how are the contacts getting dirty?
Domed keyboards have ventholes under the dome otherwise you wouldn't be able to press them when they are under the tape.
They are visible on the PCB when you open the calculator. these are not the holes for the plastic pins but the much smaller holes that look like a via. Every click some air gets out but is also sucked in.
I wouldn't be surprised hat if some of the holes get clogged these keys don't register well. But the calculator needs to be awfully dirty inside to make that happen. You can clean them with compressed air from the other side if you are in doubt.
I have no problem with the keyboard, yes its not a HP41 keyboard but that would need a completely different very expensive design.
HP41C (2x), HP41CV, HP41CX, DM41X β, DM41X, DM42, HP11C, HP48G, HP97
cdmackay
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Re: After extensive use: The keyboard

Post by cdmackay »

EM41 wrote:
Thu Jun 04, 2020 11:44 pm
cdmackay wrote:
Thu Jun 04, 2020 10:40 pm
the electrical contact is between the underside of the foil dome, and the board, surely? Since the foil is firmly stuck to the board, how are the contacts getting dirty?
Domed keyboards have ventholes under the dome otherwise you wouldn't be able to press them when they are under the tape.
ah! of course, good point, thanks.

I doubt that's the issue in my case, given it's a new board, and I cleaned it, and the foil, thoroughly, but it does explain how dirt can get in over time, thanks.
Cambridge, UK
41CL/DM41X 12/15C/16C DM15/16 71B 17B/BII/bII+ 28S 42S/DM42 32SII 48GX 50g 35s 30b/WP34S Prime G2
& Casios, Rockwell 18R :)
EM41
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Re: After extensive use: The keyboard

Post by EM41 »

I had a cat once that produced a fine dust and I had to clean a lot. Even bought a special vacuum cleaner with filters for it.
These fine particles can be sucked in trough the ventholes when the key is released and not all come out when pressed again.
HP41C (2x), HP41CV, HP41CX, DM41X β, DM41X, DM42, HP11C, HP48G, HP97
Geoff Quickfall
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Re: After extensive use: The keyboard

Post by Geoff Quickfall »

Doing calculator HP restorations one sees the following:

All classics, Woodstock’s, Spices, Voyagers, Coconuts, Pioneers, stretch Pioneers and Titans all have a transparent plastic film under the keys but over the PCA and domes. Sort of a dust and spill protection.

I always renew these with a ziplock bag section as it is close to the original thickness.

Haven’t seen the inside of the DM between the keys and the domes, any one elucidate us?

Geoff
gduncan
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Re: After extensive use: The keyboard

Post by gduncan »

I have a DM42 (SN:867) and recently bought a new DM42 (SN:5549). I bought the new calculator because I heard there were improvements to the keyboard.

Upon receiving the new calculator, the first change I noticed was the larger font size for the lettering on the faceplate. I am really liking the larger font lettering, it's great! Unfortunately, I was disappointed that some keys were not responding well. I quickly fixed the problem by cleaning the contacts with isopropyl alcohol. I did a lot of experimentation on my older DM42 to improve the keys and I was quite happy with how the keyboard worked on that calculator. I bought the new calculator mostly because I was curious to see what they might do to improve things.

After a few weeks playing with both calculators I have decided to combine my old PCB (SN:867) with the new faceplate. The old domes have a more definite "click" to them. After flexing the keys on the faceplate, I find the key action to be best with the older PCB, rather than the newer "softer" but less "clicky" domes on the new PCB (SN:5549).
jonmoore
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Re: After extensive use: The keyboard

Post by jonmoore »

Geoff Quickfall wrote:
Fri Jun 05, 2020 4:49 am
Doing calculator HP restorations one sees the following:

All classics, Woodstock’s, Spices, Voyagers, Coconuts, Pioneers, stretch Pioneers and Titans all have a transparent plastic film under the keys but over the PCA and domes. Sort of a dust and spill protection.

I always renew these with a ziplock bag section as it is close to the original thickness.

Haven’t seen the inside of the DM between the keys and the domes, any one elucidate us?

Geoff
Very interesting Geoff. I've seen similar in the relatively few HP calculators I've home serviced (Spice, Voyager and 48 series) but wasn't aware that it was a universal HP standard.

Love the idea of using food-bag plastic as a replacement. I reckon you'd need to find a bag with the lowest thickness for DM... hardware, but the fact that DM calcs allow particulate to so easily enter through the keyboard apertures is my biggest bugbear. Any strategy that increases the times between maintence cleans will be most welcome.
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