Casio fx-21 Sicentific Calculator Teardown And Repair - Page 1
Forum section: electronics / repair

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 06, 2016, 05:23:24 am
content: 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).

author: pinyoro
author_rank: Contributor
timestamp: January 06, 2016, 05:44:11 am
content: Great video. Very informative.

author: Autronic
author_rank: Contributor
timestamp: January 06, 2016, 05:10:45 pm
content: Top job on the reverse engineering and repair. I learnt a few things too.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 03:57:12 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 05:49:44 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 05:57:31 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 06:06:59 pm
content: A detail of the VFD connection.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 06:17:20 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 06:21:12 pm
content: Reverse engineering.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 06:30:42 pm
content: The end result. Three jumpers solderedà lasmd on 1mm (or thereabouts) traces, plus tinning, reflow of solder joints, and a coat of rosin dissolved in isopropyl alcohol.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 08, 2016, 06:36:07 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 20, 2016, 11:32:36 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: January 20, 2016, 11:36:57 pm
content: And now the review (for aficionados only).

author: crispy_tofu
author_rank: Super Contributor
timestamp: January 21, 2016, 12:30:26 am
content: Very nice!

author: NilByMouth
author_rank: Regular Contributor
timestamp: January 21, 2016, 03:31:17 pm
content: Aren't you supposed to take it apart first?I remember these old calculators - if you put your ear to it and press the buttons, it sings to you.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: January 21, 2016, 03:43:41 pm
content: Next time try some grey background and diffused light.

author: saturation
author_rank: Super Contributor
timestamp: January 21, 2016, 08:52:24 pm
content: 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.

author: bsfeechannel
author_rank: Super Contributor
timestamp: March 29, 2016, 05:45:15 pm
content: Thank you guys. I'm glad you like it.

author: bsfeechannel
author_rank: Super Contributor
timestamp: March 29, 2016, 05:48:15 pm
content: Quote from: HAL-42b on January 21, 2016, 03:43:41 pmNote taken. Thanks for the advice.

author: bsfeechannel
author_rank: Super Contributor
timestamp: March 29, 2016, 06:00:16 pm
content: Quote from: NilByMouth on January 21, 2016, 03:31:17 pmWow, isn't that true? The display sings! That could be the subject for a new video. Thanks for the tip.

author: maher471
author_rank: Contributor
timestamp: August 31, 2022, 07:00:08 pm
content: hi, just for information only, the little transistor behind the 2sc1317 or 2sc1173 is the 2sd467" alt="" class="bbc_img" />

author: inse
author_rank: Super Contributor
timestamp: August 31, 2022, 07:06:11 pm
content: What's this glove thing all about?

author: DiTBho
author_rank: Super Contributor
timestamp: September 01, 2022, 08:38:27 am
content: Quote from: bsfeechannel on January 08, 2016, 06:21:12 pmThanks. I need something to provide -20V to an stn lcd. Your circuit is perfect for that