buttons that don't register well

If you're having problems with the hardware of a DM42, post about them here.
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dove
Posts: 14
Joined: Sat Mar 24, 2018 11:35 pm

Re: buttons that don't register well

Post by dove » Tue Mar 27, 2018 11:07 pm

I have a recent run DM42, have handled another from the same timeframe in person, and can corroborate the reports about keyboard consistency.

The left side of my ENTER key does not click, though the right side does. By various incantations of adjusting the PCB screws, I can get the center of the ENTER key to be more tactile at the expense of the right side loosing its click. I have settled for leaving the right side clicky as it's the side I use. The ENTER key is notably stiffer than the other keys, enough that I prefer to use + to put the first number on an empty stack.

The keys are inconsistent in general, with some being much more clicky than others, and requiring various amounts of force. The feel of my SST key is my favorite. The bottom row is particularly soft and squishy with no audible click. Moreover, I am able to press the bottom row keys in such a way as to overcome the (soft) tactile bump but without the calculator registering the keystroke. It will occasional cause an input error during real calculations, but I tend to be heavy handed enough to avoid it (in part due to the habits enforced by the general stiffness of the DM42 keys across the board). This false activation seems much harder, maybe impossible, to do with the other keys, particularly the clicky ones.

In addition to toying with the PCB screws, I have taken out the PCB, studied all the parts for a while, and tried peeling back the plastic and realigning the dome for my + key. It did not have a noticeable effect, though I may not have adjusted it much, and the operation is not something I want to do too much of. From studying the components though, it seems to me that the tactile and audible nature of the metal domes is highly dependent on where exactly they are pressed, and moreover that said metal domes are not consistently lined up across the PCB. Many of them are a bit off in various directions. It's hard for me to imagine how this part of the design could be assembled quickly and cheaply while still being very consistent and accurate to the level likely needed for it to produce a consistent keyboard feel...but admittedly I don't know anything about manufacturing nor assembly.

Aside from this, it seems like there may be some slight alignment or tolerance stacking issues with the PCB alignment to the case (struts). This would be another factor that impacts the alignment of the plastic keys to the metal domes, and thus the keyboard feel. The reports of others finding variation in keyboard feel when attempting to shift the PCB around before tightening it down lends credence to this thought. I have only briefly experimented with this idea, but I did not find it to significantly impact the keys I am most concerned with (ENTER, bottom row, particularly +, etc.).

Lastly, the method of securing the bottom edge of the metal backing to the housing is not very robust, and the fit of the metal back to the rest of the calculator appears like it could be improved. The screws tighten the top edge down very well, but bulging induced by the beeper on the left side in particular causes the bottom edge (especially bottom right corner) to bulge out and remain loose. Depending on how the screws are tightened, this can lead to a very unpleasant feel to using the EXIT key beyond the other aforementioned keyboard feel issues. Essentially the whole case moves when you press in that area. By adjusting the screws I have made this less obvious, but mechanically it is still there. Placing a spacer material inside could work around this, but it would have the effect of permanently leaving the case bulged out from the housing there (as it is on the left edge, near the beeper) instead of leaving it flush (as it is on the top edge, which is what is most desirable). Really, the plastic flange in that corner that the case slips onto just needs to be modified to hold it tighter.


Overall, I am extremely happy with my DM42. I was not an HP-42S fan before obtaining this calculator, and I can definitely say it has converted me. My respect for and dependency on Thomas's wonderful work on Free42 has dramatically increased over the past few weeks, and SwissMicros's heroic efforts and success in manifesting a physical embodiment and extension in the DM42 absolutely adds something (many, many things) over the mobile app implementation. The screen, as everyone has pointed out, is chief among those things and cannot be overstated. Overall I am very happy with the design of the keyboard, but I cannot say I'm 100% satisfied with its implementation in practice. This is definitely a bit of an itch, considering that it is about 50% of the package I was looking for in a new physical calculator. However, even taking that into account, I feel that the DM42 is hands down the best tool I've ever used for calculating actual numbers (i.e. non-CAS problems) and it is absolutely the tool I will continue to reach for for that purpose for the foreseeable future. I haven't ever been made aware of any other device that would be a contender in my opinion. The mobile app Free42 and real HP-42S probably come second, but I feel the DM42 still takes the cake. I think it's saying a lot that the whole package is so strong that I unequivocally feel that way despite the keyboard feel issues.

Having said that, I'll add that as much as I'm the sort of person that would be first in line to ask for stiff clicky keys and a heavy housing, having now sat down and used them side by side, I actually think the HP-42S takes the win on these fronts with it's light, handy nature and keys that are easy on the fingers. If I needed to crunch a lot of numbers everyday, I'd probably feel this even stronger---enough so that I've toyed around with the idea of 3D printing a polymer back case for the DM42, as the calculator is quite light once you factor out the steel backing. (If someone already has a CAD model for it by any chance, let me know!) However, as the weeks have rolled on I've very much warmed up to the DM42 in these respects and occasionally felt my opinion change. So I think these things are very much in the category of "preference".

dove
Posts: 14
Joined: Sat Mar 24, 2018 11:35 pm

Re: buttons that don't register well

Post by dove » Tue Mar 27, 2018 11:30 pm

As an addendum to my already too long post... :roll:

My gut here is screaming that it's the alignment of those metal dome switches. (Though the ENTER issue might have a little more at play.) There might be some useful food for thought here: https://www.ecnmag.com/article/2010/06/ ... salignment and elsewhere in the literature. Though I'm sure SwissMicros has more knowledge and study hours in this topic than I.

If in the future there were ever an upgrade opportunity to improve the keyboard feel, I would jump at it, even if it meant additional cost.

mcc
Posts: 211
Joined: Fri Jun 23, 2017 3:10 am

Re: buttons that don't register well

Post by mcc » Wed Mar 28, 2018 6:14 am

Hi,

for the following I will not take any responsibilty for results from it -- even it may help in some cases: :))

For all that:
Take care about static electricity.

What I did to make the key board more consistence:
Remove the back
Remove the LCD flat cable at the top of the PCB
Remove both of the screws holding the PCB in place
Carefully lift and remove the PCB

Take a look at the bottom horizontal edge of the PCB
Mine has some rests of ... (how should I call that..."inter PCB connections"? Those "break here" thingies, which holds a couple
of PCBs together before they get their electronic parts soldered. After that the PCBs get broken off at that ... things. HELP!)

These [fill in missing word here] make the PCB a little longer where it should not be.

I used some super fine sandpaper to remove those [fill in missing word here].
From the PCB wipe off any residue with a dry cloth. Take care about static electricity.

After that:
Insert the PCB back into place.
Insert both PCB screws and loose tighten them so that the PCB just dont fell off.
Carefully insert back the LCD connector and fasten the socket.
Now: With a little force "press" the PCB against its bottom mount. Take care, that
the PCB dont get tilted. DONT use the USB-connector for that.
While "pressing" the PCB fasten the PCB screws alternatingly (that is: tighten the
left screw a little, than the right one, then the left one again and so on)
If the screws are tightened use some electrical tape over the screws to prevent them
to fall into the case of the DM42 and cause a short circuit somehow (some report of
a "rattling noise" of their DM42 -- which was caused by loosened screws).

Put back the stainless steal back of the DM42 and finally tighten the remaining
two screws.

This procedure makes the differences of the tactile feeling of the keyboard less
prominent. But especially with the ENTER-key and the "0"-key it is still there a little.

HTH!

Cheers!
Meino
DM 42 - SN: 00373, Firmware v.:3.14. / 3.14. as compiled by SwissMicros

dove
Posts: 14
Joined: Sat Mar 24, 2018 11:35 pm

Re: buttons that don't register well

Post by dove » Wed Mar 28, 2018 1:50 pm

mcc wrote:
Wed Mar 28, 2018 6:14 am


Take a look at the bottom horizontal edge of the PCB
Mine has some rests of ... (how should I call that..."inter PCB connections"? Those "break here" thingies, which holds a couple
of PCBs together before they get their electronic parts soldered. After that the PCBs get broken off at that ... things. HELP!)

These [fill in missing word here] make the PCB a little longer where it should not be.

I used some super fine sandpaper to remove those [fill in missing word here].
From the PCB wipe off any residue with a dry cloth. Take care about static electricity.
Yes, I know exactly what you're talking about. I noticed those too and thought the same thing. Theres another on the side too. After some thought though, I concluded that the holes in the PCB and corresponding struts in the housing completely constrain the PCB position, but maybe that's not the case. Not to mention, fine alignment is always a function of these tiny things, phase of the moon, etc.

Before I give it a shot, if I can remain patient enough: would you say that this mod has made your keys more clicky all around or less clicky?

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Walter
Posts: 1007
Joined: Tue May 02, 2017 9:13 am
Location: Close to FRA, Germany

Re: buttons that don't register well

Post by Walter » Thu Mar 29, 2018 6:12 am

dove wrote:
Wed Mar 28, 2018 1:50 pm
would you say that this mod has made your keys more clicky all around or less clicky?
Is registration a function of clickiness? :? I thought it's more a matter of proper alignment (or call it centralisation) ... and the absence of dirt (or fuzz) under the domes ...
DM42 SN: 00041 --- Follower of Platon.

HP-35, HP-45, ..., HP-50, WP 34S, WP 31S, DM16L

pauli
Posts: 52
Joined: Tue May 02, 2017 8:11 am
Location: Australia

Re: buttons that don't register well

Post by pauli » Thu Mar 29, 2018 6:34 am

I've got a couple of keys that don't always work and one (7) that sometimes works, sometimes misses and sometimes double registers.

Pauli

User avatar
Walter
Posts: 1007
Joined: Tue May 02, 2017 9:13 am
Location: Close to FRA, Germany

Re: buttons that don't register well

Post by Walter » Thu Mar 29, 2018 6:48 am

AFAIK and IIRC, this keyboard problem is the last major technical challenge SwisssMicros has to solve for the DM42.
DM42 SN: 00041 --- Follower of Platon.

HP-35, HP-45, ..., HP-50, WP 34S, WP 31S, DM16L

mcc
Posts: 211
Joined: Fri Jun 23, 2017 3:10 am

Re: buttons that don't register well

Post by mcc » Thu Mar 29, 2018 11:20 am

dove wrote:
Wed Mar 28, 2018 1:50 pm
mcc wrote:
Wed Mar 28, 2018 6:14 am


Take a look at the bottom horizontal edge of the PCB
Mine has some rests of ... (how should I call that..."inter PCB connections"? Those "break here" thingies, which holds a couple
of PCBs together before they get their electronic parts soldered. After that the PCBs get broken off at that ... things. HELP!)

These [fill in missing word here] make the PCB a little longer where it should not be.

I used some super fine sandpaper to remove those [fill in missing word here].
From the PCB wipe off any residue with a dry cloth. Take care about static electricity.
Yes, I know exactly what you're talking about. I noticed those too and thought the same thing. Theres another on the side too. After some thought though, I concluded that the holes in the PCB and corresponding struts in the housing completely constrain the PCB position, but maybe that's not the case. Not to mention, fine alignment is always a function of these tiny things, phase of the moon, etc.

Before I give it a shot, if I can remain patient enough: would you say that this mod has made your keys more clicky all around or less clicky?
Hmmm...difficult to say...especially for a non-native speaker...

The result is more a matter of more/less than of works/doesn't work (or TRUE/FALSE).
Before removeing those...(damn, can someone tell me how to name these... correctly, please? ;) ) I had an either/or-case:
Either the ENTER key works with the tactile feeling and clickiness of ...of a strawberry...and "0" works OK...
or "0" were sometimes a "" (no contact).
In a frist attemp I tilted the board until the "0" works and a starwberry on my keyboard, since a "" instead of a "0" on a calculator
than a swampy (but working) ENTER.

The mod seem to de-tilt the board: Either you get a working "0" and a better tactile feedback with the ENTER key or both get more worse -- but is
fixable by pushing the PCB against its bottom holder and fasting the PCB while still pushing the PCB.

The mod does not make a IBM model M from a cheap NoName ruberdome keyboard though (NOT COMPARING the DM42 keyboard with a cheap rubber dome here!!!)

The next thing which seems to have an influence could be the black spongy ... (again missing a word here) thingy on the battery holder.
When closing the DM42 it seems to me, that that spongy something is compressed by the steal back and presses on the PCB in turn.
Since it does this in the upper left corner it may also """shear""" (by the amount of 2 and half wavelength of green light at most ;) the PCB.

For what is that spongy something good for? Electrical insolation could be done with some tape...

@Michael?

Another thing: Since the PCB-screws are machine screws which counterpart are metal inserts (THIS is a sign of quality! The cheap version are
self taper screws, which bore their way to the pastic themselves...I dont like those that much...), there is no real serious friction between
both. The PCB does constantly """move""" (wavelength...light...you know) from using the calculators keyboard, which undo that PCB screws
a little bit (one even fell into the casing with my DM42...that's why I put some tape over them now) step by step. A misalignment of the
PCB and the metal domes is the result and it needs another aligning-PCB-fastening-the-screws-session then as it seems.
ATTENTIONE! I am not talking about things which needs to be done 3 times a week or so...! And all this may or may not only apply to my
DM42 only. The mod may gradually fix the problem but not for all time -- it need to be redone from time to time.

May be this could be part of a starting point for a real fix...would be nice...

Cheers!
Meino
DM 42 - SN: 00373, Firmware v.:3.14. / 3.14. as compiled by SwissMicros

gduncan
Posts: 13
Joined: Sat Mar 03, 2018 2:18 pm

Re: buttons that don't register well

Post by gduncan » Thu Mar 29, 2018 1:03 pm

I think each metal dome has its own unique action, or click response. I assume this because I swapped my right ENTER dome, which clicked loudly with my EXIT dome, which was too mushy. The result is that the EXIT key now clicks nicely and my ENTER key (on the right side) feels much, much better.
Maybe I am fortunate, because by working on the keyboard myself I now like the way each key feels with the exception of the left side of ENTER. It's unfortunate if other users aren't able to get their DM42's to feel consistent somehow...
I too would be in favor of an SM upgrade to the key feel. I would pay for my current machine to be upgraded, or even buy a new DM42 with the fixes.

mcc
Posts: 211
Joined: Fri Jun 23, 2017 3:10 am

Re: buttons that don't register well

Post by mcc » Thu Mar 29, 2018 2:57 pm

Hi gduncan,

...whow!... :)
I myself would not have the guts to do such low-level mods on my DM42.

But I think a have found another clue:
I think there two reasons for a key for not being clicky.
And there are two reasons for a key for not giving contact.

Clicky/not clicky
Reason one: The nob (this spikey thing on the bottom side of the key) on the key is not centered over the midth of the metal dome. The dome is move down tilted, which prevents it to click.
Reason two: The nob is centered but it is already compressing the dome beyond the "point of click" (P.O.C. ;) ) but not far enough to give contact.

Contact/no contact
Reason one: dirt on the contacts under the dome. Can be fixed by those who are able to do such "low level mods"... :)
Reason two: The key does not click. Why that? When plotting the force to press the key over the way the key travels the force increases much just before the dome clicks. At that moment all saved potential energy of the bended dome is released and the dome """crashes""" onto the copper
of the contacts.
Whith a swampy/mushy key the only force is the force of the comparable slowly moving key - that's why those give contact nevertheless if the
key is pressed hard.

Is there any suspicious "something" near the left side of the ENTER key, why may cause the "pre-trigger" of the left dome of the ENTER key?
Since several people (including me) experience a mushy left and a freshly clicking right side of the key it may be not based on a DM42, which
has higher tolerances but by something more consistant?

PS: I have some dust under the glass of the LCD, which is clearly visible, when the sun or a lamp throws its photons with a shallow angle onto
the LCD...any idea how to remove it?

Cheers
Meino
DM 42 - SN: 00373, Firmware v.:3.14. / 3.14. as compiled by SwissMicros

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