Plotting to Restore a r0tring CS-50

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If youā€™re of a certain vintage and have ever done any technical drawing, chances are good that you used a r0tring of some kind, be it pencil or pen. Well, r0tring makes more than writing implements.  They also made electronic scribers ā€” a small plotter that pens ISO lettering on technical drawings based on typed input. This was a huge time saver over doing it freehand or stenciling each letter. The CS-50 is designed to hold the top-of-the-line r0tring drawing pen, which turned out to be the most expensive part of this restoration aside from the time spent sniffing out issues.

[Atkelar] likes to open things up and give them a visual inspection before powering them on. We think this is good practice, even if the suspense kills you. But really, [Atkelar] did so much more than that. He started by replacing the likely late-80s-era coin cell even though it registered north of 3 V. Then he swapped out all the electrolytic caps and one tantalum, cleaned the rubber dome keyboard parts with a cheap electric toothbrush, (another great idea), and completely disassembled the x-y mechanism to clean and re-oil it.

Building a new screw boss with cyanoacrylate glue and baking soda.
Glue boss!

Then came the moment of truth. The input works and shows up on the screen, but the steppers donā€™t move. The waveform from the motors looked good, but seemed to be over voltage by about 3 V. Although [Atkelar] couldnā€™t find a manual online, he did find a blog post about this machine that confirmed 15 V on the steppers is right.

As it turns out, there was a ground issue. The sheathing of the power cable acts as a common ground, so pressing it against the bottom plate of the disassembled case made steppers work. But after a while, they quit. [Atkelar] cleaned terminals, but nothing had changed ā€” the steppers would work for a while and then stop.

We thought this would turn into a Fail of the Week for sure, but [Atkelar] checked more of the motor pins and found that one of the driver chips was dead. Fortunately, he found a replacement and the thing works like new. Check out the complete restoration video after the break, and look for our favorite part. Thatā€™s when [Atkelar] molded a new screw boss end by building a wall with polyimide tape and filling up the cavity with cyanoacrylate glue and baking soda.

In the mood for more restorations? You canā€™t go wrong with something by [drygol], thatā€™s for sure.

Thanks for the tip, [macsimski]!



from Blog ā€“ Hackaday https://ift.tt/3F0Cuvr

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