EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: bsfeechannel on January 06, 2016, 05:23:24 am
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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.
https://www.youtube.com/watch?v=-qJebvO23Y8 (https://www.youtube.com/watch?v=-qJebvO23Y8)
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).
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Great video. Very informative.
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Top job on the reverse engineering and repair. I learnt a few things too.
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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.
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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.
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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.
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A detail of the VFD connection.
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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.
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Reverse engineering.
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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.
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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.
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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.
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And now the review (for aficionados only).
https://www.youtube.com/watch?v=cSqwNg7-NMw (https://www.youtube.com/watch?v=cSqwNg7-NMw)
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Very nice! :-+
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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.
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:-+
Next time try some grey background and diffused light.
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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.
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Thank you guys. I'm glad you like it.
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Next time try some grey background and diffused light.
Note taken. Thanks for the advice.
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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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hi, just for information only, the little transistor behind the 2sc1317 or 2sc1173 is the 2sd467(http://[attachimg=1])
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What's this glove thing all about?
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Reverse engineering.
Thanks. I need something to provide -20V to an stn lcd. Your circuit is perfect for that :-+