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Re: buttons that don't register well

Posted: Wed Apr 18, 2018 5:36 pm
by mcc

I had some kind of a partly sucessful hack of some sort ...
(being careful here... ;)

I measured the resistance of the foam on the battery holder...infinite high.
So I think its purpose has nothing to do with grounding static electricity.
To get rid of one point where the PCB may get bend due to uncontrolled pressure
I removed the foam from the battery holder and replaced it with a piece of electrician tape.
The other point where mechanical stress is put onto the PCB is the beeper, which is slightly too high for
the case of the DM42...I will not remove that one of course.

Next I carefully opened the LCD clip and freed its contact strip.
Then if removed the PCB screws and removed the PCB.
Right above the two holes for the PCB screws (keyboard side where the
clicky domes are) I put two of this sticky points (word?) one onto the other
above each hole (so 2,2,+ in sum): ... 00VZDB7V2/
(This is only an example. Any other sticky point of this size will do. No advertisement intended!)
"Wetterfest" is german for "weatherproof". The one I used were simple colored paper dots. Nothing "wetterfest"...
as said: Only as an exanmple...

This way the PCB is positioned a little higher, if the screws are fastened.

I still have a dull left EN- and a clicky right -TER. But the overall clickyness is a little better now.

With this little paper dots, which could be stacked, it should be possible to balance/level the PCB in
a way, that -- despite fastened screws -- the overall clickyness will be restaurated/regained.
I dont believe that it will possible to get a equally clickified EN- and -TER, though.


Re: buttons that don't register well

Posted: Thu Apr 19, 2018 4:56 am
by Rmollov
Michael wrote:
Wed Apr 18, 2018 7:13 am
Rmollov wrote:
Wed Apr 18, 2018 7:08 am
The above may be one of the reasons, but there is another as can be seen on the photos...
That looks strange. Please take it completely apart, gently press the enter button from behind and put it back together.
I hope it solves the issue.
Thanks Michael, that worked. Apparently the main problem here (I'm not talking contamination under domes, assuming domes click fine) is the imperfection of the plastic keyboard layer.
My observations: actual keys are held in position by 2 thin "bridges" and fixing the alignment by gently pressing them with fingernails seem to do the job. This applies to all keys, but the negative effect is mainly with the ENTER key - the 2 plastic buds at the back of the key *must* be perfectly aligned (especially in height) above the domes. Then you get a single click pressing ENTER in the middle. I also fixed my STO key and now it sits better in position, even though there is no difference in the feel or action to before.
My PCB has a slight bulge, but I'm not sure that is the problem; fine & precise re-alignment of each key probably is the best solution.



Re: buttons that don't register well

Posted: Sun Apr 22, 2018 9:00 pm
by dove
Michael wrote:
Thu Apr 12, 2018 11:13 am
I'm sorry for this. Finally we nailed the problem with the ENTER button.
The unequal tactile feedback is caused by the upwards bent ABS housing.
Once the calculator is taken apart and warmed up a little, it can be bent back which should solve the issue.
Please give it a try. Otherwise you can send it back to me and I'll fix it.
Guys, I do NOT recommend following this advice.

Having what I think is a good sense of what Michael is talking about, against my better judgement I let impatience get the best of me and I attempted to follow his advice sans instructional video. I disassembled then warmed the housing with a hair dryer and tried to unbend it. Not only did this not fix the left side of my ENTER key, but it ruined a few other of my keys (RCL, 1/X). The keys ended up stuck down. I had to diassemble again, reheat, and then try to rebend those keys outward from the inside, taking care not to accidentally press on any other keys since I figured that's what must have caused this. I managed to get those keys somewhat bent out, but then noticed now my LOG key was ruined. Repeat again. Now CLX and F6 were ruined. Repeat. Sigma+. Repeat. In all cases I took great care not to depress the keys, but they seemed to bend themselves out of nowhere. I even took care to only heat from the inside lest the hair dryer's fan be the culprit for depressing the keys.

I succeeded in making each of these keys usable again, but now they have become significantly lighter than the other keys. In short, the consistency of the keyboard has been made noticeably worse, to the point that it is now downright distracting and unpleasant for me to use. And the ENTER key remains unfixed...

At this point, I'll be emailing SM to inquire what replacement or refund options I have. I cannot currently count myself as a satisfied customer.

I appreciate SM fostering the tinkering spirit here in this community, but these hardware tweaks---particularly reforming plastic---are not things they should be advising customers to attempt. I knew that, and I should have listened to myself. Lesson learned.

ETA: Michael was very generous and offered to repair/replace as needed. My DM42 is off to SM. Looking forward to seeing how it turns out!

Re: buttons that don't register well

Posted: Sun Apr 29, 2018 12:24 pm
by gduncan
dove wrote:
Sun Apr 22, 2018 9:00 pm
ETA: Michael was very generous and offered to repair/replace as needed. My DM42 is off to SM. Looking forward to seeing how it turns out!
That's great! Please post an update once you receive the new or repaired DM42. I'm mostly curious to find out if your ENTER key is fixed.

Re: buttons that don't register well

Posted: Wed May 02, 2018 8:44 pm
by giubeca
Me too.

Re: buttons that don't register well

Posted: Thu May 03, 2018 6:57 am
by H2X
giubeca wrote:
Wed May 02, 2018 8:44 pm
Me too.
Me three!

Re: buttons that don't register well

Posted: Thu May 03, 2018 8:42 pm
by dove
Haha, will do. It should end up at SM around May 7th.

5/5 ETA: On it's way back from SM :D

Re: buttons that don't register well

Posted: Sun May 20, 2018 11:49 am
by cesar
I have done a low-tech hacking of the DM42 keyboard. One of the problems I had was the asymmetry of the ENTER key. It works well by pressing on the right side of the key. I had tried to adjust the back screws and some more tricks that I read on the forums, without success.

What worked for me? I have compensated for the small difference between the left/right side of the ENTER key and the dome with a thickness of two pieces of post-it paper cut out for the indicated size.

I hope it's useful to someone. Now it works perfectly!!!! The ENTER key can be pressed at any point.

Re: buttons that don't register well

Posted: Mon May 21, 2018 4:18 am
by mcc
Hi Cesar,

only to check whether I have understood your hack correctly:
You put this two pieces/stripes of post-it above the left or the right
dome of the ENTER key (looking at the DM42 from the front side
and the calculator oriented with the usb pointing away from you) ?

Thanks a lot for the hack!
(Before knowing the DM42 I would have never thought that I would
ever hack a pocket calculator with a piece of post-it... ;)


Re: buttons that don't register well

Posted: Mon May 21, 2018 9:40 am
by Rmollov
I think you tried to cure the consequence rather than the reason.
Would you post here a photo of the ENTER key from the top?
I really doubt its top surface is parallel to the face plate, if it works after changing the geometry underneath.
It's highly unlikely motherboard has such a huge bow to allow for compensation like that.