restoring a Compuchron (Hughes) led calculator

[albertofenini]

ciao a tutti, in a recent lot, among the others, was the piece of history :

IMG01671.jpg

I was tolding it was not working, so not surprise when it really didn't.
However, these are two more pictures, back cover :

IMG01670.jpg

and module inside the case :

IMG01669.jpg

now, if you browse the internet, you will see something like this :
http://www.crazywatches.pl/compuchron-hughes-aircraft-calculator-led-1976

I have the feeling that mine is missing few pieces, like metal springs for the side buttons,
battery covers, can anyone please help me in understanding ?

I will post a reply myself to this post with a fourth picture to show where the small pcb part came off from
thanks again Alberto

[albertofenini]

This is the fourth picture :

IMG01672.jpg

Thanks again Alberto

[albertofenini]

I have followed the instruction on the web page and the module is now ready for cleaning,
the question is ... what can I use for cleaning the ceramic and the rest of the pieces ?
I will leave the opening of the keyboard unit as the last thing to do.
Still, if anyone has an idea on how to rebuild the missing parts, or have additional pics
where I can see the missing parts, particulary the springs for the side buttons
I will greatly appreciate any help !!

IMG01685.jpg

IMG01686.jpg

IMG01687.jpg

more pictures on the next message ...

[albertofenini]

the rest of the pictures (for now) :

IMG01688.jpg

IMG01690.jpg

IMG01692.jpg

take care and thanks for any info or idea !
Alberto

[azimuth_pl]

hi Alberto,
you don't need the button springs to check if the module works so focus on the repair first - you can always insert any metal object in the button hole and connect the case with the solder spot on the ceramic module.
you have a different model so you are not missing battery hatches/covers.
I would first clean the module with alcohol or even dip the bottom side of the ceramic in mild acid like lemon juice or vinegar and then rinse in demineralized water.
you can clearly see a heavy residue from battery leakage and the trimmer is all black from the fumes...turn it and clean.
check all connections and try again.
if there any breakage to the ceramic please check if the PCB holds properly, if the board is split in half then you will have quite a challenge to fix this piece.

[albertofenini]

ciao Azimuth_pl,

I did the cleaning with vinegar, and I must say that the results are very good,
I did clean the display, the flex cable and the keyboard unit, and the module.

I have also taken apart the quartz and trimmer unit, in the next picture you
will see it "remounted". The crack is thin but on both sides and when "reinstalling" the
quartz module, the pressure necessary to push the clip made it break in two.

The cover that protect the ICs lifted and I was able to see underneath, which
means that probably some bound wires are now broken.

IMG01710.jpg

IMG01711.jpg

As of now, I'm not pushing anymore the upper clip, but I'm sure the quartz module
is not making contact and I believe the module is badly damaged.

What do you think ?
Do you know af any source for a spare module ??

I would like to test the display, do you know the pinout ?
It would be nice to know if it can be used in future as spare parts.

Please let me know your feedback,
thanks for help, Alberto

[azimuth_pl]

You might be out of luck with that crack.
If you are persistent then glue the ceramic, open the circuitry cover and check for any broken wirebonds.
With a cracked board you will not only have to repair wirebonds but also solder broken traces on the board.
This is doable but only on less complex modules...this one would take forever and still might not be successfull.
Spare modules are nowhere to find.

Good luck!
Piotr

[Seiko&Casio Lcd's]

Sorry to see that the board is cracked alberto , could hanno repair it ?

[azimuth_pl]

the number of possibly faulty wirebonds is difficult to define but it might be a large number.
with a certain price for repairing each wirebond the service would be quite expensive and still you might not end up with a working watch.
not worth the effort IMO as there are several possible rootcauses aside the cracked board.

[albertofenini]

I think you are right,
I will give it a try after the holiday season,
at first I would like to try the display to check if there are missing segments.
Does anyone know the pinout and the voltage ?
I was thinking of applying 3 Vcc to the contacts and see if the I can get it
lightning correctly.

Anyone knows the electrical scheme of the display ?
Thanks for help
Alberto

[azimuth_pl]

I doubt it's 3V for the display, it should be far less but I don't know exactly.
I am not aware of the diagram being available anywhere.

[albertofenini]

I usually test LCD segments functionality using an ohm-meter
by moving the positive and negative terminals along the LCD
display. Do you think it would work or it would ruin it ?
thanks again Alberto

[azimuth_pl]

it will work on a LED but you have to check the proper voltage