48sx repair help



#9

Hello,

I used the instructions created by Han to open the 48sx so that I could fix a non-working keyboard row.

I used a thin piece of rubber between the existing keyboard rubber strip and the keyboard connector as a shim.
My thoughts were that this would help provide the missing contact for the keyboard row.

I accidently disturbed the lower rubber 'zebra strip?' that provides contact for the LCD.
The unit is back together (right side does not snap back well enough).
It does not power on unless I press down on the right side of the bezel below the LCD.
And even then, the LCD is missing many columns after powering on.

Q's:

1. What is the proper way to clean and reinsert the rubber strip for the LCD.

2. Is there a better way to provide 'gap reduction' for the keyboard contact than what I did?
A whole new rubber piece, or can it be shimmed in the manner in which I attempted.

3. What is causing the power-on problem?

4. What would cause the right side to not snap back together as well as the left?
I know this side was more difficult to pry apart.

Obviously, I am open to suggestions and criticism. The unit was working fine except the keyboard row not working prior to my repair attempt. The unit is at home at the moment.

Edited: 2 Feb 2011, 7:21 a.m.


#10

I have used trimmed foam from a Dr Scholls insole to replace the old foam and repair the contact.

I have wiped down the zebra strips with alcohol and been very careful to not contaminate when re-assembling. Dust from the PCB can interfere with the contact. I have had the same problem with dropped lines too and found that keeping the zebras clean and making sure you apply enough pressure on the board before you twist the metal tabs are key to a successful repair.


#11

Quote:
I have used trimmed foam from a Dr Scholls insole to replace the old foam and repair the contact.

I have wiped down the zebra strips with alcohol and been very careful to not contaminate when re-assembling. Dust from the PCB can interfere with the contact. I have had the same problem with dropped lines too and found that keeping the zebras clean and making sure you apply enough pressure on the board before you twist the metal tabs are key to a successful repair.


I just wanted to add so emphasis to this response. Keep in mind that your problems are usually because of a loose connection between the printed circuit board and the connectors themselves. So your problems even after your attempted fix is either:

1) the insert you added was too thick or unevenly inserted so that part of the contacts touch the circuit board and other parts do not (and this would also cause gaps between the LCD connector and the circuit board)

2) you did not fasten the circuit board tight enough.

When I fasten the board back on, I make sure to apply lots of (even) pressure to ensure that the connection is tight, and then fasten the twist tabs.

#12

Thank you for the responses. I opened it back up last night, and used a foam piece from a mouse pad to replace the keyboard foam strip.
This seems to have fixed the keyboard contact issue. However, the LCD dropped rows/columns still exists.
I did clean the zebra strips using alcohol, and it is better than before. I would estimate that 50% of the LCD does not light up.
When pressure is applied above the A and F keys, the entire LCD does light up.
I did apply pressure to the PCB before turning the tabs, but fear that my initial tightening was not the greatest and has caused the connection to loosen.
Are replacement zebra strips available with larger thickness? That would certainly help in this case. Many thanks!


#13

Quote:
Thank you for the responses. I opened it back up last night, and used a foam piece from a mouse pad to replace the keyboard foam strip.
This seems to have fixed the keyboard contact issue. However, the LCD dropped rows/columns still exists.
I did clean the zebra strips using alcohol, and it is better than before. I would estimate that 50% of the LCD does not light up.
When pressure is applied above the A and F keys, the entire LCD does light up.
I did apply pressure to the PCB before turning the tabs, but fear that my initial tightening was not the greatest and has caused the connection to loosen.
Are replacement zebra strips available with larger thickness? That would certainly help in this case. Many thanks!

My only suggestion is to apply more pressure to the points of contact as twist the 6 tabs. The other thing that I do is prior to affixing the circuit board, I straighten out the tabs so that their prongs. Lastly, keep the number of times you twist these tabs to a minimum -- they will break if you are overzealous.

Also, you may want to look from the side to see if there is a lack of contact. Using just your fingers to press the circuit board back into place, can you notice any air gap near where the LCD connectors are? It sounds to me that your foam may be a bit too thick and not as spongy as is needed to allow for enough compression so that the LCD connectors make contact with the circuit board.


#14

Yes, there is a gap at the same location that I disturbed the zebra strip.
It is on the right side of the LCD (when looking at the assembled unit).
The other parts of the PCB do not show a gap. The tabs are still twisted at the moment.
I tried yesterday to reinsert that side of the zebra strip, but it does not seat fully in its track.
Is there a trick to get it in there? Also, I also noticed the metal frame is bent so that the keyboard side is bent up slightly.
I will fix that once I disassemble again. But before I untwist the tabs, I wuuld like to get your experience on seating the zebra strip.
Many thanks!


#15

Quote:
Also, I also noticed the metal frame is bent so that the keyboard side is bent up slightly.

Success!! The metal frame was bent at the 'F' key location. This caused 2 things: the zebra strip had some wiggle room between the lcd and the frame, and since the frame was bent upwards, the zebra was not making proper contact with the lcd and pcb. My keys are restored, and the lcd is working 100%. The case is not as tight as before, but I am an amateur ;)

Some Pictures


#16

Congrats! That it works is more than good enough for a first attempt at fixing your own calculator.


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