Author Topic: Casio fx-21 Sicentific Calculator Teardown And Repair  (Read 8942 times)

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Offline bsfeechannel

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Casio fx-21 Sicentific Calculator Teardown And Repair
« on: January 06, 2016, 05:23:24 am »
Long time unregistered lurker, registered today. First post.

Inspired by Dave's most important creation (besides his kids) I decided to shoot a video about the teardown and repair of a Casio fx-21 Scientific Calculator, a VFD display beast from the nineteen seventies.



Never edited and published a video before. I just wanted to know how it was to be like Dave when it comes to produce a video with meaningful content. It is not an easy task. Lemme tell ya.

Although the result is less than amateur, I hope you have fun.

P.S.: Voice-over, courtesy of Google Translator (too much noise in the "studio" for live audio).
 

Offline pinyoro

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #1 on: January 06, 2016, 05:44:11 am »
Great video. Very informative.
 

Offline Autronic

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #2 on: January 06, 2016, 05:10:45 pm »
Top job on the reverse engineering and repair. I learnt a few things too.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #3 on: January 08, 2016, 03:57:12 pm »
Glad you like, guys.

To complement the information in the video I thought I'd post some "hires" photos, starting with the calculator in one piece.



 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #4 on: January 08, 2016, 05:49:44 pm »
Now some view of the internals. Notice the residue of the leaked battery electrolyte in the back of the housing. That probably caused the corrosion to the main board traces. And the dirt accumulated on the angular selection switch. All of this was removed with isopropyl alcohol.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #5 on: January 08, 2016, 05:57:31 pm »
The boards are single-sided phenolic. Hence the profusion of jumpers. The keyboard matrix board (previous post) has flat jumpers on the same side of the copper and the contacts are gold-plated.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #6 on: January 08, 2016, 06:06:59 pm »
A detail of the VFD connection.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #7 on: January 08, 2016, 06:17:20 pm »
Detail of the corrosion. It can be clearly seen where the trace for digit number 5 was interrupted. But other traces were in bad shape also and required the same kind of intervention.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #8 on: January 08, 2016, 06:21:12 pm »
Reverse engineering.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #9 on: January 08, 2016, 06:30:42 pm »
The end result. Three jumpers soldered à la smd on 1mm (or thereabouts) traces, plus tinning, reflow of solder joints, and a coat of rosin dissolved in isopropyl alcohol.
« Last Edit: January 20, 2016, 11:22:50 pm by bsfeechannel »
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #10 on: January 08, 2016, 06:36:07 pm »
So there you have it. Whether you're a calculator aficionado, a repairman in need of information, or just a curious bystander, I hope this will be of some help. Have fun.

 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #11 on: January 20, 2016, 11:32:36 pm »
One more photo with a detail showing a template of the correct order of the keys printed in the casing. Very handy if you need to remove them for cleaning. On the right you can see the power connector, the positive battery contact and the on-off switch.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #12 on: January 20, 2016, 11:36:57 pm »
And now the review (for aficionados only).

 

Offline crispy_tofu

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #13 on: January 21, 2016, 12:30:26 am »
Very nice!  :-+
 

Offline NilByMouth

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #14 on: January 21, 2016, 03:31:17 pm »
Aren't you supposed to take it apart first?  :-/O

I remember these old calculators - if you put your ear to it and press the buttons, it sings to you.
 

Offline HAL-42b

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #15 on: January 21, 2016, 03:43:41 pm »
 :-+

Next time try some grey background and diffused light.
 

Offline saturation

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #16 on: January 21, 2016, 08:52:24 pm »
Great job.  I think I owned one of those in that series, IIRC they ate batteries.  At the time Casio was innovating with calculators almost every 6 mo or so, coming out with more functions, better battery life, and smaller sizes, solar powered, until finally plateauing to what we have today, the $9 FX260, before moving on to the education focused VPAM style.

Best Wishes,

 Saturation
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #17 on: March 29, 2016, 05:45:15 pm »
Thank you guys. I'm glad you like it.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #18 on: March 29, 2016, 05:48:15 pm »
Next time try some grey background and diffused light.

Note taken. Thanks for the advice.
 

Offline bsfeechannel

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Re: Casio fx-21 Sicentific Calculator Teardown And Repair
« Reply #19 on: March 29, 2016, 06:00:16 pm »
I remember these old calculators - if you put your ear to it and press the buttons, it sings to you.

Wow, isn't that true? The display sings! That could be the subject for a new video. Thanks for the tip.
 


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